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Accelerated Degradation of Perfluorosulfonates and Perfluorocarboxylates by UV/Sulfite + Iodide: Reaction Mechanisms and System Efficiencies

  • Zekun Liu
    Zekun Liu
    Department of Chemical & Environmental Engineering, University of California, Riverside, California 92521, United States
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  • , 
  • Zhanghao Chen
    Zhanghao Chen
    State Key Laboratory of Pollution Control and Resource Reuse, School of the Environment, Nanjing University, Nanjing 210023, Jiangsu, China
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  • Jinyu Gao
    Jinyu Gao
    Department of Chemical & Environmental Engineering, University of California, Riverside, California 92521, United States
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    Orcidhttps://orcid.org/0000-0002-1751-3430
  • , 
  • Yaochun Yu
    Yaochun Yu
    Department of Chemical & Environmental Engineering, University of California, Riverside, California 92521, United States
    Department of Civil & Environmental Engineering, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, United States
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    Orcidhttps://orcid.org/0000-0001-9231-6026
  • , 
  • Yujie Men
    Yujie Men
    Department of Chemical & Environmental Engineering, University of California, Riverside, California 92521, United States
    Department of Civil & Environmental Engineering, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, United States
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    Orcidhttps://orcid.org/0000-0001-9811-3828
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  • Cheng Gu
    Cheng Gu
    State Key Laboratory of Pollution Control and Resource Reuse, School of the Environment, Nanjing University, Nanjing 210023, Jiangsu, China
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    Orcidhttps://orcid.org/0000-0002-6939-7101
  • , and 
  • Jinyong Liu*
    Jinyong Liu
    Department of Chemical & Environmental Engineering, University of California, Riverside, California 92521, United States
    *Email: [email protected], [email protected]
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    Orcidhttps://orcid.org/0000-0003-1473-5377
Cite this: Environ. Sci. Technol. 2022, 56, 6, 3699–3709
Publication Date (Web):February 28, 2022
https://doi.org/10.1021/acs.est.1c07608

Copyright © 2022 American Chemical Society. This publication is licensed under

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Abstract

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The addition of iodide (I–) in the UV/sulfite system (UV/S) significantly accelerated the reductive degradation of perfluorosulfonates (PFSAs, CnF2n+1SO3–) and perfluorocarboxylates (PFCAs, CnF2n+1COO–). Using the highly recalcitrant perfluorobutane sulfonate (C4F9SO3–) as a probe, we optimized the UV/sulfite + iodide system (UV/S + I) to degrade n = 1–7 PFCAs and n = 4, 6, 8 PFSAs. In general, the kinetics of per- and polyfluoroalkyl substance (PFAS) decay, defluorination, and transformation product formations in UV/S + I were up to three times faster than those in UV/S. Both systems achieve a similar maximum defluorination. The enhanced reaction rates and optimized photoreactor settings lowered the EE/O for PFCA degradation below 1.5 kW h m–3. The relatively high quantum yield of eaq– from I– made the availability of hydrated electrons (eaq–) in UV/S + I and UV/I two times greater than that in UV/S. Meanwhile, the rapid scavenging of reactive iodine species by SO32– made the lifetime of eaq– in UV/S + I eight times longer than that in UV/I. The addition of I– also substantially enhanced SO32– utilization in treating concentrated PFAS. The optimized UV/S + I system achieved >99.7% removal of most PFSAs and PFCAs and >90% overall defluorination in a synthetic solution of concentrated PFAS mixtures and NaCl. We extended the discussion over molecular transformation mechanisms, development of PFAS degradation technologies, and the fate of iodine species.

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Synopsis

Adding iodide in the UV/sulfite system significantly enhanced the reaction rate, energy efficiency, and chemical utilization for reductive defluorination of various per- and polyfluoroalkyl substance pollutants.

Introduction

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Per- and polyfluoroalkyl substances (PFASs) have become global pollutants (1) due to their (i) wide applications since the 1940s, (ii) high recalcitrance in natural environments, and (iii) diverse toxicities to animals (2,3) and health concerns for humans. (4−7) While carbon sorption, (8,9) ion exchange, (9−11) and membrane filtration (12,13) can capture PFAS from polluted water, the subsequent treatment of the concentrated PFAS remains challenging. (14−16)
Among the rapidly developing technologies for PFAS degradation, (17−23) photochemical treatment with UV-generated electron (eaq–) has demonstrated great promise for environmental remediation. (24−34) The C–F bond can be reductively converted into C–H by eaq– (eq 1), (25,29) which can be generated from UV irradiation of SO32– (eq 2) with a quantum yield (QY) at 0.12–0.14 mol/einstein (35,36)
(1)
(2)
Although the 254 nm irradiation used in common water treatment applications is not the maximum absorption wavelength of SO32–, (36) the cost-effectiveness of PFAS degradation by UV/sulfite (UV/S) has been greatly enhanced by tuning reaction conditions, such as pH adjustment. (37) At pH 12.0, the defluorination has reached 73–93% for n = 2–8 perfluorocarboxylates (CnF2n+1COO–, PFCAs) and 79–84% for n = 4, 6, 8 perfluorosulfonates (CnF2n+1SO3–, PFSAs). (38) The C–H bonds in the UV/S treatment residue allow for further defluorination by oxidation with HO•, resulting in near-complete defluorination. (38) However, PFSAs are intrinsically more recalcitrant than PFCAs for UV/S treatment. The short-chain n = 4 perfluorobutane sulfonate (PFBS, C4F9SO3–) is even more challenging than longer-chain n = 6, 8 PFSAs. (25,29) Multiple spikes of sulfite and >24 h are required to degrade all parent PFBS, (38) resulting in high chemical dosage and energy consumption for an effective treatment.
Before the application of UV/S for pollutant degradation, (26,36) UV/iodide (UV/I) had been developed earlier for PFAS degradation. (24,25,39) The generation of eaq– from iodide (eq 3) has a QY at 0.22–0.29 mol/einstein (40,41)
(3)
A previous study reported >95% defluorination of perfluorooctanoate (C7F15COO–, PFOA, an extensively studied “representative” PFAS) by UV/I at pH 9.2 and ambient temperature. (42) Although a higher concentration of eaq– could be expected from UV/I than UV/S, our use of UV/I only achieved PFOA defluorination of up to 60% (see Table A2 of the Supporting Information of ref (29)). The low efficiency could be attributed to eaq– scavenging by reactive iodine species (RIS, e.g., I2, I2•–, and I3–) and dissolved oxygen (DO). (25,39) While DO removal by N2 was necessary for UV/I, N2 purge is not necessary for UV/S (29) because the initial DO can be rapidly scavenged by sulfite. (43) Therefore, we added sulfite to simplify the DO removal for UV/I. To our surprise, the degradation and defluorination of the highly recalcitrant PFBS were significantly accelerated even at a 10-fold higher concentration than our previous studies (i.e., 250 vs 25 μM). To date, the UV/sulfite + iodide (UV/S + I) system has only been examined for reductive degradation of monochloroacetate (44) and bromate (45) in 2018. The first report on dechlorination by UV/S + I (44) has revealed key mechanistic insights to understand the enhanced degradation of highly recalcitrant PFAS. Herein, we systematically optimized the UV/S + I system using the PFBS as the challenging probe, elucidated the reaction mechanisms using various model fluorinated compounds, and showcased the significantly enhanced system efficiencies in both chemical dosing and energy consumption for the degradation of legacy PFSAs and PFCAs.

Materials and Methods

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Chemicals

Sodium sulfite (Na2SO3), potassium iodide (KI), sodium hydroxide (NaOH), and sodium bicarbonate (NaHCO3) were purchased from Fisher Chemical. PFSAs (n = 4, 6, 8 CnF2n+1SO3–, PFSAs) and PFCAs (n = 1–8 CnF2n+1COO–) were purchased in bulk quantities (i.e., 0.1–5 g) and used as received. The information on CAS numbers, purities, and vendors are listed in Supporting Information.

Photochemical Reaction

The optimization of UV/S + I system parameters used the previously reported photochemical reactor configuration (Ace Glass parts #7864-10, #7874-38, and #7506-14, wrapped with aluminum foil). (29,46) A 600 mL solution containing 25 μM PFBS, 5 mM NaHCO3, and predetermined concentrations of KI and Na2SO3 and pH (adjusted with NaOH) was irradiated by an 18 W low-pressure mercury lamp (GPH212T5L/HO) in the closed photoreactor with jacketed water cooling at 20 °C. For the reduction of energy consumption, the optimized solution condition was further applied in a new reactor configuration, where a 2000 mL solution was irradiated by a 10 W low-pressure mercury lamp (GPH212T5L, with the same geometry as the 18 W lamp) in a quartz sleeve placed in the center of a 2 L tall-form beaker (wrapped with aluminum foil and covered by a plastic cap with parafilm sealing). Because the 2 L beaker did not have a water cooling jacket, the solution was gradually heated from 20 to 36 °C in the first 4 h by the UV lamp and then maintained around 36 °C due to the balance with heat dissipation.

Water Sample Analysis

The parent PFAS and transformation products (TPs) were analyzed by liquid chromatography–high-resolution quadrupole Orbitrap mass spectrometer (LC–HRMS/MS). Both suspect and non-target screening were conducted to identify TPs. Short-chain (n = 1 and 2) PFCAs and their TPs were analyzed by ion chromatography (IC). The degradation kinetics were fit with C/C0 > 0.2 data using the pseudo-first-order kinetic model. Rationales for this fitting method are described in Text S1. The released fluoride ion (F–) was measured by an ion-selective electrode (ISE) and validated by IC. (29,38) Detailed operation parameters of LC–HRMS/MS, IC, and ISE have been reported previously (29,32,37,38) and also included in the Supporting Information. The defluorination percentage (deF%) is defined as the molar ratio between the released F– in solution and the total F in the parent PFAS compounds.

Laser Flash Photolysis

A transient absorption spectrometer (LP980, Edinburgh Instruments) equipped with 266 nm laser pulse (Nd:YAG) (34) was used to measure the yield and lifetime of eaq– produced from UV/S, UV/I, and UV/S + I. The sample solution (2.5 mL) containing KI and Na2SO3 at predetermined dosage was filled in a 1 cm × 1 cm × 3 cm quartz cell and then purged with N2 for 30 min. The solution was then excited by the laser beam along with the 1 cm optical path. The absorption by eaq– and I3– was measured at 700 (34) and 350 nm, (47) respectively. The lifetime of eaq– and I3– was calculated by eq 4
(4)
where Rt is the signal response at time t, B is the amplitude of the absorption curves at time zero, τ represents the time required for the response to decay to 37% of the original signal strength, and the fitted τ is defined as the lifetime. (34)

Results and Discussion

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Significantly Accelerated PFBS Degradation by UV/S + I

Previously, we have used PFOA as the probe to optimize the UV/S system (pH 12.0 and 10 mM Na2SO3). (37) However, when the target pollutant was switched to PFBS, the optimized UV/S only achieved 48% decay of the parent PFBS (Figure 1a) and 42% overall defluorination after 24 h (Figure 1b). (38) To enhance the degradation, two more spikes of 10 mM Na2SO3 at 8 and 16 h (i.e., 30 mM Na2SO3 in total) boosted the parent PFBS decay and overall defluorination to 86 and 69%, respectively. (38) In sharp contrast, the addition of 2 mM KI to 10 mM Na2SO3 in the UV/S system substantially accelerated the reaction by reaching >99% decay of the parent PFBS and 78% overall defluorination after 24 h, without additional Na2SO3 spikes during the reaction. Thus, I– not only accelerated the reaction but also significantly enhanced the utilization efficiency of SO32–. Notably, for most samples from different reaction settings and sampling times, the deF% from the reacted portion of the PFBS was consistent (i.e., 83 ± 2%). Therefore, the decay of the parent PFBS is the rate-limiting step and the following defluorination from TPs is fast. (29)

Figure 1

Figure 1. (a) Parent compound decay and (b) defluorination of PFBS by UV/S (10 mM), UV/I (2 mM), and UV/S (10 mM) + I (2 mM); PFBS degradation by UV/S + I at varied (c,d) iodide concentrations, (e) sulfite concentrations, and (f) solution pH. Default reaction conditions: PFBS (0.025 mM), carbonate (5 mM), pH 12.0, 254 nm irradiation (an 18 W low-pressure Hg lamp in 600 mL solution), and 20 °C.

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We continued using the highly recalcitrant PFBS to further optimize the UV/S + I system. The examination on varying concentrations of I–, SO32–, and pH (Figure 1c–f) confirmed that the initially used 2 mM I–, 10 mM SO32–, and pH 12.0 constitute the optimal reaction conditions for 0.025 mM PFBS. The use of ≤5 mM SO32– led to early termination of defluorination (Figure 1e) probably due to the early depletion of sulfite. Further elevated concentrations of either SO32– (e.g., 20 mM) or I– (e.g., 5 mM) did not result in a better performance. In our previous study on the UV/S system, 10 mM SO32– was found to be necessary to achieve the maximum defluorination of 0.025 mM PFOA. (37)

Energy Efficiency of the UV/S + I System

We further confirmed the high energy efficiency of UV/S + I from the rapid degradation of n = 6, 8 PFSAs and n = 1–7 PFCAs (Table 1). The first-order rate constants for the parent compound decay were 2.4–4.1-fold of those by UV/S, where all conditions were the same except for the absence of iodide. The term EE/O, which is defined as the electrical energy consumed for lowering the pollutant concentration by one order-of-magnitude (i.e., C/C0 = 0.1 or 90% removal), has been frequently used for water technology evaluation (48)
where P is the power of the UV lamp (kW), k is the first-order rate constant (h–1), and V is the volume of water (m3). To probe the possibility of further lowering the EE/O by UV/S + I, we decreased the power of the UV lamp from 18 to 10 W and increased the volume of water from 600 to 2000 mL. The decay of the parent PFAS in the new configuration of 10 W: 2000 mL was 20–50% slower than in the previous configuration of 18 W: 600 mL. Hence, the EE/O values were reduced by 3–5-fold from modifying the reactor configuration (see Text S2 for an extended discussion). Together with the acceleration by iodide, the EE/O for n = 2–7 PFCAs by UV/S + I have become <1.5 kW h/m3 (Table 1). Interestingly, the maximum deF% of PFCAs by UV/S in the 10 W: 2000 mL configuration was significantly lower than that in the 18 W: 600 mL configuration (Figure S1). In stark comparison, defluorination of PFCAs by UV/S + I in the 10 W: 2000 mL configuration only showed a lower initial rate, but the maximum deF% after 4 h was the same as in the 18 W: 600 mL configuration.
Table 1. DeF%, Rate Constant, EE/O, and EE/Max.deF of PFCAs and PFSAs by UV/S and UV/S + I Treatmenta
  defluorination after 1 h (%) parent compound decay k (h–1)b EE/O (kW h m–3)b EE/Max.deF (kW h m–3)b
PFCA(CnF2n+1COO–) UV/S UV/S + I UV/S UV/S + I UV/S UV/S + I UV/S UV/S + I
n = 1 TFA 84 ± 1.2 100 ± 1.3 3.7 (2.4) 8.6 (6.8) 18.6 (4.8) 7.8 (1.7) <60 (10) <22.8 (3.8)
n = 2 PFPrA 47 ± 0.4 75 ± 0.9 6.7 (4.9) 17.2 (8.9) 10.2 (2.3) 4.2 (1.3) <240 (40) <60 (20)
n = 3 PFBA 52 ± 2.1 77 ± 0.8 5.8 (3.5) 19.2 (9.9) 12.0 (3.3) 3.6 (1.2) <240 (40) <120 (20)
n = 4 PFPeA 42 ± 3.9 73 ± 1.5 5.5 (3.4) 16.9 (8.7) 12.6 (3.4) 4.2 (1.3) <240 (40) <120 (20)
n = 5 PFHxA 51 ± 3.1 79 ± 1.3 6.1 (4.1) 19.7 (10.1) 11.4 (2.8) 3.6 (1.1) <240 (40) <60 (20)
n = 6 PFHpA 41 ± 2.7 77 ± 3.6 5.4 (3.7) 17.5 (9.4) 12.6 (3.1) 4.2 (1.2) <240 (60) <60 (20)
n = 7 PFOA 39 ± 1.5 88 ± 0.3 5.2 (3.1) 15.4 (8.1) 13.2 (3.7) 4.2 (1.4) <240 (60) <60 (20)
  defluorination after 24 h (%) parent compound decay k (h–1) EE/O (kW h m–3) EE/Max.deF (kW h m–3)
PFSA (CnF2n+1SO3–) UV/S UV/S + I UV/S UV/S + I UV/S UV/S + I UV/S UV/S + I
n = 4 PFBS 43 ± 1.8 78 ± 1.2 0.05 (0.02) 0.19 (0.05) 1320 (576) 366 (230) ∼1320 (576) ∼366 (230)
n = 6 PFHxS 60 ± 3.1 84 ± 1.3 0.38 (0.29) 1.56 (0.61) 181 (39.7) 44.4 (18.9) <360 (60) <120 (40)
n = 8 PFOS 84 ± 0.9 92 ± 0.7 0.78 (0.65) 1.90 (1.01) 88.8 (17.7) 36.6 (11.5) <240 (40) <60 (40)
a

Reaction conditions were the following: individual PFCA/PFSA (0.025 mM), Na2SO3 (10 mM), KI (2 mM), NaHCO3 (5 mM), pH 12.0, 254 nm irradiation (an 18 W low-pressure Hg lamp in 600 mL solution), and 20 °C.

b

Values in parentheses are from an “energy-saving” setting (a 10 W lamp in 2 L solution, solution constituents not changed) at 20–36 °C due to the gradual heating by the UV lamp without a cooling water bath.

For the much more recalcitrant PFSAs, the EE/O were also lowered to 11.5–230 kW h/m3. As elucidated in our previous study, (29) one primary mechanism for parent PFCA decay is hydrodefluorination of the α −CF2– moiety, and one primary mechanism for parent PFSA decay is the reductive cleavage of the C–S bond. Because both mechanisms require the reaction with eaq–, the significantly accelerated degradation of both PFCAs and PFSAs by UV/S + I can be attributed to the enhanced availability of eaq–.
As the goal of PFAS degradation is not merely removing 90% of the parent compound, we propose a new metric that calculates the electrical energy consumed by the time (t) upon reaching 90% of the maximum defluorination (EE/Max.deF, Table 1)
Because defluorination involves multiple pathways and cannot be quantified with a simple kinetic model, the EE/Max.deF values are estimated as a range based on the time when the first sample showing >90% of the maximum defluorination was collected. The maximum defluorination was determined in the sample taken at 24 h when sulfite had been fully depleted (see Figure 6c).
For PFCAs, the parent compound decay was much faster than the stepwise defluorination (Figure 2a vs b,c). The decay and defluorination of n ≥ 2 PFCAs followed similar time profiles, so the average values are shown in those figures. Still, their EE/Max.deF values by UV/S + I were <20 kW h m–3. For PFSA degradation, the parent compound decay and defluorination were much more synchronous (Figure 2d–f) than PFCA degradation. Because >90% parent compound decay of PFSAs is the pre-requisite for reaching 90% of the maximum defluorination, the EE/Max.deF values for PFSAs were also higher than their EE/O. The current reactor configuration and solution composition of UV/S + I have resulted in the low-end EE/O values for PFOA/PFOS degradation among existing reports on various technologies. (16,19,23,49) Currently, the comparison of EE/Max.deF with other treatment methods is not feasible due to the lack of reported defluorination-time profiles, especially for PFBS degradation.

Figure 2

Figure 2. (a) Parent compound decay and (b) defluorination of n = 1–7 PFCAs by UV/S (10 mM), and UV/S (10 mM) + I (2 mM). Panel (c) shows the magnified defluorination profiles for n = 2–7 PFCAs (averaged) within the first 1 h. (d–f) Parent compound decay and defluorination of n = 4, 6, 8 PFSAs. Reaction conditions: individual PFAS (0.025 mM), NaHCO3 (5 mM), pH 12.0, 254 nm irradiation (an 18 W low-pressure Hg lamp in 600 mL solution), and 20 °C.

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Mechanistic Insights from Reaction Kinetics and TPs

To understand how the new UV/S + I system accelerated both parent compound decay and defluorination, we used n = 1 and 2 PFCAs (CnF2n+1COO–) as mechanistic probes. Short-chain PFCAs have a limited number of fluorinated carbons, and many possible TPs have commercial standards for quantitation. The decay and defluorination of the three n = 1 structures, CF3–COO– (trifluoroacetate, TFA), CHF2–COO– (difluoroacetate, DFA), and CH2F–COO– (monofluoroacetate, MFA) by UV/S + I were significantly faster than those by UV/S (Figure 3a–c vs d–f). While the complete defluorination by UV/S took 2–4 h, only 1 h was needed for UV/S + I. The formation of acetate (CH3–COO–) indicates the hydrodefluorination pathway, where F atoms were stepwise replaced by H atoms via reduction with eaq– (Figure 3g). The generation (and degradation) of the stepwise hydrodefluorination TPs (e.g., DFA and MFA from TFA) was also faster in the UV/S + I system. Meanwhile, the various gaps of the acetate yield from 100% indicate the competing decarboxylation pathway (Figure 3g). At the end of reactions where 100% defluorination was achieved, the acetate yields from DFA and MFA by UV/S + I (72 and 93%, respectively) were higher than those by UV/S (45 and 72%, respectively). The preferred hydrodefluorination indicates enhanced availability of eaq– in the UV/S + I system.

Figure 3

Figure 3. Parent compound decay, TP formation, and defluorination of tri-, di-, and monofluoro acetates by (a–c) UV/S + I and (d–f) UV/S and (g) reaction schemes. Reaction conditions: individual PFAS (0.025 mM), Na2SO3 (10 mM), KI (2 mM), NaHCO3 (5 mM), pH 12.0, 254 nm irradiation (an 18 W low-pressure Hg lamp in 600 mL solution), and 20 °C. The vertical red dotted lines in panels (d–f) indicate the 1 h time window where 100% defluorination by UV/S + I was achieved.

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However, for the degradation of TFA, the acetate yield by UV/S + I (34%) was lower than that by UV/S (52%). The calculated C–F bond dissociation energy (BDE) in TFA (116.8 kcal mol–1) is significantly higher than those in DFA (109.7 kcal mol–1) and MFA (108.6 kcal mol–1). (29) We have also found that the C–F bonds in CF3CH2–COO– (121.5 kcal mol–1) and HCF2CH2–COO– (118.8 kcal mol–1) were both sluggish in the reaction with eaq–. (37,50) Therefore, the dominating pathway for TFA degradation by UV/S + I should be decarboxylation.
The degradation of CF3CF2–COO– (PFPrA, see Table 1 for acronyms) using UV/S + I was also significantly faster than that by UV/S (Figure 4a,b vs c,d). The recalcitrant hydrodefluorination TP, CF3CH2–COO–, has very strong sp3 C–F bonds (Figure 4e) and thus is accumulated in the solution. Both UV/S + I and UV/S achieved a similar deF% of PFPrA (79% in Figure 4a and 76% in 4c), suggesting that UV/S + I cannot cleave additional C–F bonds that are recalcitrant under UV/S treatment. However, upon reaching the maximum deF%, the yield of CF3CH2–COO– from UV/S + I treatment was higher than that from UV/S treatment (62 vs 39 from 250 μM of PFPrA), indicating enhanced availability of eaq– for hydrodefluorination of the relatively weak C–F bonds. Notably, the limit of deF% via hydrodefluorination is 40% (i.e., two α C–F bonds out of the five C–F bonds in PFPrA are cleaved), whereas the overall deF% reached 79%. The deeper defluorination is thus contributed by the decarboxylation pathway, which mineralized the α CF2 moiety and yielded TFA (Figure 4e). TFA can be 100% defluorinated by either pathway (Figure 3).

Figure 4

Figure 4. Parent compound decay, TP formation, and defluorination of PFPrA by (a,b) UV/S + I and (c,d) UV/S. Panels (b,d) show magnified time profiles within the first hour of reaction. Panel (e) shows the proposed reaction schemes. Reaction conditions: PFPrA (0.025 mM), Na2SO3 (10 mM), KI (2 mM), NaHCO3 (5 mM), pH 12.0, 254 nm irradiation (an 18 W low-pressure Hg lamp in 600 mL solution), and 20 °C.

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It is worth noting that other degradation pathways also occurred. As shown by the F balance counting F– and known TPs from hydrodefluorination (CF3CFH–COO– and CF3CH2–COO–) and from decarboxylation (TFA, DFA, and MFA were negligible), the maximum gap reached >50% at the beginning (15 min for UV/S + I and 1 h for UV/S). After the maximum deF% was achieved (8 h for UV/S + I and 24 h for UV/S), the missed F balance was decreased to 6% for UV/S + I and 15% for UV/S. While we are investigating novel TPs with other mechanistic hypotheses, we noted that most F-containing TPs did not escape the system as gaseous products because the following oxidation with HO• (generated from heat-activated persulfate at pH > 12) achieved ∼100% defluorination. (38)
The abovementioned mechanistic insights were further corroborated by the results from C7F15–COO– (PFOA). The generation and the following degradation of the decarboxylation product, C6F13–COO– (PFHpA), and the hydrodefluorination product, C7F14H–COO–, were much faster by UV/S + I than by UV/S (Figure 5a vs b). We note that the detected concentration of a TP is the result of the balance between generation and degradation at the same time. Although the maximum concentrations of those two TPs under UV/S + I and UV/S were similar, their total generated amounts under UV/S + I should be more than those under UV/S.

Figure 5

Figure 5. Parent compound decay and TP formation for the degradation of (a,b) PFOA and (c,d) PFBS by UV/S + I and UV/S. Panel (e) shows the proposed reaction schemes. Reaction conditions were the following: individual PFAS (0.025 mM), Na2SO3 (10 mM), KI (2 mM), NaHCO3 (5 mM), pH 12.0, 254 nm irradiation (an 18 W low-pressure Hg lamp in 600 mL solution), and 20 °C.

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TP analysis for the degradation of C4F9–SO3– (PFBS) also confirmed that the formation of the hydrodefluorination product, C4F7H2–SO3–, was significantly enhanced by UV/S + I (Figure 5c vs d). According to the calculated C–F BDEs for PFSAs, (29) the most probable location for the initial hydrodefluorination is on the β carbon (Figure 5e). Further hydrodefluorination only yielded C4F6H3–SO3–, which accumulated under UV/S + I treatment. Hence, the high overall deF% of 79% should also be attributed to C–S cleavage upon the reaction between C4F9–SO3– and eaq– to yield n ≤ 3 PFCAs (Figure 5e). However, PFCA TPs (e.g., PFBA) were not detected, probably due to the rate-limiting decay of the PFBS and the rapid degradation of daughter PFCAs.

Mechanistic Insights from Reactive Species Analyses

The significantly accelerated parent compound decay and the increased yield of hydrodefluorination products by UV/S + I prompted us to explain the enhanced availability of eaq–. We compared the abundance and lifetime of eaq– produced from UV/S + I, UV/S, and UV/I by measuring the absorption at 700 nm in laser flash photolysis (LFP) experiments (Figure 6a). As expected from the reported QY, the abundance of eaq– generated by the 266 nm laser from 2 mM I– (absorbance 0.012, QY = 0.22–0.29 mol/einstein) (40,41) was approximately two times higher than that from 10 mM SO32– (absorbance 0.016, QY = 0.12–0.14 mol/einstein) (35,36) at pH 12. However, the eaq– from UV/I has a 22-fold shorter lifetime than that from UV/S. Besides the quenching by H+ (eq 5), a series of RIS can rapidly form (eqs 6–8) and become strong scavengers of eaq– (eqs 9–11). (25,39) This may be one reason for the limited performance of UV/I for PFAS degradation. (39,44,51,52)
(5)
(6)
(7)
(8)
(9)
(10)
(11)

Figure 6

Figure 6. (a) Kinetic profiles of transient absorption at 700 nm after the 266 nm laser pulse excitation of I, S, and S + I solutions; (b) kinetic profiles of transient absorption at 350 nm after 266 nm laser pulse excitation of I and S + I solutions; (c) decay of sulfite in UV/S and UV/S + I in the absence of PFAS; and (d) lifetime of eaq– in UV/S + I at varied solution pH. Conditions: Na2SO3 (S, 10 mM), KI (I, 2 mM), and pH 12.0.

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For comparison, UV/S + I generated eaq– in a similar abundance to UV/I. Meanwhile, the lifetime of eaq– in UV/S + I was eightfold longer than that in UV/I (Figure 6a). Besides serving as the source of eaq– (eq 2), SO32– has also been found to rapidly reduce RIS back to I– (eqs 12–15) (53,54)
(12)
(13)
(14)
(15)
As I3– has a characteristic absorption at 352 nm, (39,44) the rapid quenching of I3– by SO32– was also confirmed by the LFP experiment (Figure 6b). The use of 10 mM SO32– shortened the lifetime of I3– by 23-fold. Although a radical reaction network remains challenging to build, a simplified interpretation is that SO32– donates up to two electrons to convert RIS back to I– via eqs 12–15. This interpretation is consistent with (i) the faster consumption of SO32– in UV/S + I than in UV/S (Figure 6c), (ii) the generation of eaq– in high abundance and long lifetime in UV/S + I, and (iii) the enhanced reductive PFAS degradation. These experimental findings complement the previous study on monochloroacetate degradation, which conducted meticulous kinetic measurements for a comprehensive mechanistic understanding of the UV/S + I system. (44) Moreover, SO32– is an instant scavenger of DO without UV irradiation. (43) Upon adding Na2SO3 in water, the measured DO immediately dropped from 7.3 to <0.1 mg/L. Thus, the use of SO32– effectively prevented eaq– quenching by DO, (25,26) and the UV/S + I system does not need N2 purge.
In addition, the lifetime of eaq– at pH from 9 to 12 showed an increasing trend (Figure 6d). Because the speciation of both I– and SO32– is not impacted at pH > 10, the longer lifetime at higher pH is primarily attributed to the reduced eaq– quenching by H+ (eq 5). This result is consistent with the excellent PFBS degradation kinetics at pH 12 (Figure 1f).

Iodide Significantly Enhanced the Utilization of Sulfite

In our previous studies on the UV/S system, the typical concentration of PFOA was 25 μM because higher concentrations resulted in inferior performance. For example, using 10 mM SO32– at pH 12, the defluorination of 25 μM of individual n = 2–7 PFCAs reached 73–93% at 8 h. The kinetics did not show a significant dependence on the fluoroalkyl chain length (n). However, the deF% from 250 μM (or 0.25 mM) of individual PFCAs were significantly lowered and exhibited an obvious decrease with the increased n (Figure 7a). For PFOA, 0.25 mM of C7F15–COO– contained 3.75 mM of the C–F bond. If 100% defluorination could be achieved solely by the hydrodefluorination mechanism (eq 1), up to 7.5 mM of eaq– would be consumed. However, the use of 10 mM SO32– in UV/S only achieved 34% defluorination at 24 h, where most SO32– had been depleted (Figure 6c). Under UV irradiation, the major portion of SO32– that was not utilized for PFAS degradation probably generated H2 gas. (35) However, this aspect warrants further investigation. Additional spikes of 10 mM SO32– enabled further defluorination, but a total of 40 mM SO32– only defluorinated PFOA up to 73% (Figure 7b). In stark contrast, the initially added 10 mM SO32– and 2 mM I– directly achieved 84% defluorination from the 0.25 mM PFOA within 12 h. Thus, the utilization of sulfite was significantly enhanced by the addition of iodide. Further increasing the PFOA concentration to 0.5 mM led to significantly lower defluorination (Figure 7c). Hence, we increased the concentration of all PFCAs and PFSAs from 25 to 250 μM. The UV/S + I treatment of PFCAs achieved a similar deF% for both concentrations (Figure 7d). The UV/S + I treatment of n = 4, 6, 8 PFSAs (0.25 mM) without spiking additional SO32– also achieved 68, 81, and 87% of defluorination, respectively (Figure 7e). These values are consistent with the maximum deF% of n = 4, 6, 8 PFSAs (25 μM) by UV/S with additional SO32– spikes (69, 72, and 84%, respectively). (38)

Figure 7

Figure 7. (a) DeF% of PFCAs by UV/S after 8 h; (b) time profiles for the defluorination from 0.25 mM PFOA by UV/S (with SO32– spikes every 24 h) and UV/S + I (no SO32– spike); (c) time profiles for the defluorination from various [PFOA]0 by UV/S + I; (d) deF% of PFCAs after 24 h by UV/S + I; (e) deF% of PFSAs by UV/I and UV/S + I after 24 h; (f) time profiles for the defluorination from the mixed PFAS (see Table 2) in NaCl brine after a 1:1 dilution with deionized (DI) water. Default reaction conditions: 10 mM Na2SO3 (10 mM), KI (2 mM for UV/S + I), NaHCO3 (5 mM), pH 12.0, and 254 nm irradiation (an 18 W low-pressure Hg lamp for 600 mL solution), and 20 °C.

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Motivated by these positive results, we further challenged the UV/S + I system to treat a synthetic brine, which was prepared based on the NaCl content and quantified PFAS constituents in a recently reported “still bottom” waste brine from ion-exchange resin regeneration (Table 2). (16) Natural organic matters and other potential inhibiting species that require pretreatment efforts were not included in the present study. Individual PFAS component concentrations were chosen as the averaged values of the six reported brines. (16) Commercially unavailable structures (e.g., n = 5, 7, 9 PFSAs), minor structures (e.g., n = 9 PFCA and n = 8 sulfonamide), and unknown PFAS precursors were not included. Hence, the synthetic brine contained 3 wt% NaCl and a total of 10.9 mM of C–F bonds in the mixture of three fluorotelomer sulfonates (FTSAs, n = 4, 6, 8 CnF2n+1–CH2CH2–SO3–), six PFCAs (n = 3–8), and three PFSAs (n = 4, 6, 8). We diluted the brine for twofold, so that the eaq– generated from 10 mM SO32– and 2 mM I– would suffice the need for cleaving all C–F bonds (5.5 mM after dilution) via the reductive pathway (eq 1). The UV/S + I treatment achieved 90 and 93% defluorination from this brine sample after 12 and 24 h, respectively (Figure 7f). The UV/S treatment using 50 mM SO32– exhibited an inferior rate and extent of defluorination. Quantitation of the individual PFAS in the treated brine found that a majority of parent structures have been removed for >99.5%. The outstanding substrates exhibiting high recalcitrance included PFBS (94% removal) and 4:2 FTS (52% removal). Hence, short-chain fluorotelomers are not ideal for direct UV/S + I treatment. The isolation of the very short fluoroalkyl chain by −CH2– moieties voids the favorable mechanistic factors for PFAS degradation: (1) vulnerable C–F bonds in the middle of long fluoroalkyl chains, (2) weak α C–F bonds in PFCAs, and (3) the dissociation of C–S bonds in PFSAs. (29)
Table 2. Treatment of a Concentrated PFAS Mixture in NaCl Brine by UV/S + Ia
PFAS category compound PFAS concentration (μg L–1) total fluorine in C–F bonds (μg L–1) residual PFAS after 24 h (μg L–1)b parent PFAS removal ratio (%)
FTSAs 4:2 FTS 131 68 63 51.9
  6:2 FTS 27,950 16,124 296 98.9
  8:2 FTS 875 535 <53 >93.9
PFCAs PFBA 1950 1212 <5 >99.7
  PFPeA 5872 3803 <13 >99.7
  PFHxA 16,433 10,936 <8 >99.9
  PFHpA 7492 5083 <9 >99.8
  PFOA 101,550 69,896 <10 >99.9
  PFNA 228 159 <12 >94.7
PFSAs PFBS 4988 2522 279 94.4
  PFHxS 72,550 40,893 <88 >99.8
  PFOS 86,950 56,155 <100 >99.8
sum   327.0 mg L–1 207.4 mg L–1 (10.9 mM) <0.9 mg L–1 >99.7
a

Reaction conditions: the 3% NaCl brine with the tabulated components was diluted with 1:1 DI water, Na2SO3 (10 mM), KI (2 mM), NaHCO3 (5 mM), pH 12.0, 254 nm irradiation (an 18 W low-pressure Hg lamp in 600 mL solution), and 20 °C.

b

Concentrations without a definitive value indicate the limit of quantitation by the HRMS instrument in our study. These values are the HRMS-detected concentration multiplied by 2 (due to the 1:1 dilution before treatment). Solid-phase extraction for accurate quantitation in low concentration ranges (e.g., the prevalent 70 ng L–1 reference for drinking water) was not used in this proof-of-concept study.

Implications to PFAS Degradation Research and Engineering

Our experimental results collectively suggest that the use of iodide in UV/S + I significantly benefits PFAS degradation by (i) increasing the concentration of eaq– (Figure 6a) and (ii) increasing the utilization of sulfite (Figure 7b). Mechanistic probing experiments (Figures 3–5) identified similar transformation pathways at much higher rates by UV/S + I than by UV/S. While all reaction steps were significantly accelerated upon the addition of I–, the maximum deF% remained the same. The consumptions of both electricity (Figure 2 and Table 1) and chemical (Figure 7) by UV/S + I are significantly lower than those by UV/S. Although the results have established a highly efficient photochemical system and provided mechanistic insights to the best of our current research capability, this single report cannot cover all details from fundamental understanding to practical application. For example, the interactions between various sulfur and iodine species are much more complex than the proposed, as shown in eqs 5–15. (39,44,55) However, a comprehensive and accurate reaction network modeling can be established upon deeper understandings of reactions for individual reactive species with PFASs and their TPs. Further elucidation of PFAS degradation pathways and mechanisms should be prioritized for future research efforts. After all, we have provided detailed data sets that confirm UV/S + I as a potential engineering solution for PFAS destruction. Although iodinated gaseous products were reported in earlier studies using UV/I, (25) the accumulation of polar iodinated organics from UV/S + I treatment is less likely because (i) C–I bonds are highly vulnerable to eaq– reduction and UV photolysis (44) and (ii) RIS are rapidly scavenged by SO32–.
For PFAS degradation technology development, we highlight the importance of investigating a broad range of structures rather than the legacy PFOA/PFOS. We have shown that the reactivity of PFAS highly depends on the chain length and functional groups. (29,32,50) This study provides an example of using the highly challenging C4 PFBS as the probe for technology development. As expected, the optimized UV/S + I system exhibits significantly enhanced performance for all PFCAs and C6 and C8 PFSAs. Still, like UV/S, the UV/S + I system is mechanistically limited for treating short-chain fluorotelomers. (38) Thus, oxidation is required both before and after the UV/S + I treatment to ensure efficient and complete defluorination of most PFAS pollutants. (38) NOM and other potential inhibiting species in real “still bottom” brines will also be addressed in our near-future study on sequential treatment strategies.
Lastly, iodide is a relatively expensive chemical enriched from seawater, but we do not consider the cost of iodide as a major barrier for practical applications of UV/S + I. The volume of waste brine from ion-exchange resin regeneration is minimal. The real cost of both the electricity and chemicals for PFAS destruction in the waste brine is to be divided by the large volumes of drinking water or groundwater treated by ion exchange. However, when iodide recycling is necessary, iodine species in the treated brine can be rapidly transformed into either I– (e.g., eqs 12–15) or I2 (e.g., by H2O2) (56) for facile separation. I– has a much higher affinity to ordinary anion exchange resins than common anions (e.g., F–, Cl–, SO42–, and HCO3–/CO32–), (57) and I2 can be extracted by common organic solvents from water. For example, at 25 °C the solubility of I2 in diethyl ether (25 wt%) is substantially higher than that in water (∼300 mg/L). (58)

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The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/acs.est.1c07608.

  • Details of PFAS chemicals; quantitation of PFAS parent compounds, TPs, and anions; extended discussions on kinetic data fitting and photoreactor configurations; and defluorination profiles in the two photoreactor configurations (PDF)

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  • Corresponding Author
  • Authors
    • Zekun Liu - Department of Chemical & Environmental Engineering, University of California, Riverside, California 92521, United States
    • Zhanghao Chen - State Key Laboratory of Pollution Control and Resource Reuse, School of the Environment, Nanjing University, Nanjing 210023, Jiangsu, China
    • Jinyu Gao - Department of Chemical & Environmental Engineering, University of California, Riverside, California 92521, United States;  Orcidhttps://orcid.org/0000-0002-1751-3430
    • Yaochun Yu - Department of Chemical & Environmental Engineering, University of California, Riverside, California 92521, United States;  Department of Civil & Environmental Engineering, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, United States;  Orcidhttps://orcid.org/0000-0001-9231-6026
    • Yujie Men - Department of Chemical & Environmental Engineering, University of California, Riverside, California 92521, United States;  Department of Civil & Environmental Engineering, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, United States;  Orcidhttps://orcid.org/0000-0001-9811-3828
    • Cheng Gu - State Key Laboratory of Pollution Control and Resource Reuse, School of the Environment, Nanjing University, Nanjing 210023, Jiangsu, China;  Orcidhttps://orcid.org/0000-0002-6939-7101
  • Notes
    The authors declare no competing financial interest.

Acknowledgments

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Financial support was provided by the Strategic Environmental Research and Development Program Project ER18-1289 (for Z.L., J.G., and J.L.) and Project ER20-1541 (for Y.Y. and Y.M.).

References

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    Environmental Science & Technology (2020), 54 (13), 8291-8299CODEN: ESTHAG; ISSN:0013-936X. (American Chemical Society)
    Epidemiol. evidence regarding the effects of in utero exposure to per- and polyfluoroalkyl substances (PFAS), particularly short-chain PFAS, on fetal reproductive hormones is limited and inconsistent. This study aimed to assess the relationship between maternal PFAS exposure and fetal reproductive hormones. A total of 752 mother-infant pairs who were recruited in the Shanghai Birth Cohort Study between 2013 and 2016 were selected. We quantified 10 PFAS, including two short-chain PFAS congeners (perfluorobutanesulfonate, PFBS and perfluoroheptanoic acid, PFHpA), in maternal blood plasma in early pregnancy. Dehydroepiandrosterone sulfate (DHEA-S), sex hormone-binding globulin (SHBG), LH, FSH and total testosterone (TT) were measured in the umbilical cord blood using chemiluminescence kits. Free androgen index (FAI) was calcd. by TT divided by SHBG. Multiple linear regression found that one ln-unit increase in maternal PFBS was assocd. with decreases in FSH (-0.159; 95% CI: -0.290, -0.029), LH (-0.113; 95% CI: -0.221, -0.004), and FAI (-0.009; 95% CI: -0.017, -0.001). In addn., PFHpA showed neg. assocns. with LH (-0.154; 95% CI: -0.297, -0.011) and FAI (-0.008; 95% CI: -0.014, -0.002). When PFAS were analyzed in quartiles, significant neg. assocns. were obsd. between PFBS and FSH, and between PFHpA and FAI. Overall, prenatal exposure to PFBS and PFHpA was assocd. with the disturbance of fetal gonadotropins as well as free androgen level in this prospective cohort, suggesting that the reproductive toxicity of short-chain PFAS may not be neglected.
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  7. 7
    Zheng, G.; Schreder, E.; Dempsey, J. C.; Uding, N.; Chu, V.; Andres, G.; Sathyanarayana, S.; Salamova, A. Per- and polyfluoroalkyl substances (PFAS) in breast milk: Concerning trends for current-use PFAS. Environ. Sci. Technol. 2021, 55, 7510– 7520,  DOI: 10.1021/acs.est.0c06978
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    7
    Per- and polyfluoroalkyl substances (PFAS) in breast milk: Concerning trends for current-use kPFAS
    Zheng, Guomao; Schreder, Erika; Dempsey, Jennifer C.; Uding, Nancy; Chu, Valerie; Andres, Gabriel; Sathyanarayana, Sheela; Salamova, Amina
    Environmental Science & Technology (2021), 55 (11), 7510-7520CODEN: ESTHAG; ISSN:0013-936X. (American Chemical Society)
    This is the first study in the last 15 years to analyze per- and polyfluoroalkyl substances (PFAS) in breast milk collected from mothers (n = 50) in the United States, and our findings indicate that both legacy and current-use PFAS now contaminate breast milk, exposing nursing infants. Breast milk was analyzed for 39 PFAS, including 9 short-chain and 30 long-chain compds., and 16 of these PFAS were detected in 4-100% of the samples. The .sum.PFAS concn. in breast milk ranged from 52.0 to 1850 pg/mL with a median concn. of 121 pg/mL. Perfluorooctanesulfonic acid (PFOS) and perfluorooctanoic acid (PFOA) were the most abundant PFAS in these samples (medians 30.4 and 13.9 pg/mL, resp.). Two short-chain PFAS, including perfluoro-n-hexanoic acid (PFHxA, C6) and perfluoro-n-heptanoic acid (PFHpA, C7), were detected in most of the samples with median concns. of 9.69 and 6.10 pg/mL, resp. Anal. of the available breast milk PFAS data from around the world over the period of 1996-2019 showed that while the levels of the phased-out PFOS and PFOA have been declining with halving times of 8.1 and 17 years, resp., the detection frequencies of current-use short-chain PFAS have been increasing with a doubling time of 4.1 years.
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  8. 8
    Xiao, X.; Ulrich, B. A.; Chen, B.; Higgins, C. P. Sorption of poly- and perfluoroalkyl substances (PFASs) relevant to aqueous film-forming foam (AFFF)-impacted groundwater by biochars and activated carbon. Environ. Sci. Technol. 2017, 51, 6342– 6351,  DOI: 10.1021/acs.est.7b00970
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    8
    Sorption of Poly- and Perfluoroalkyl Substances (PFASs) Relevant to Aqueous Film-Forming Foam (AFFF)-Impacted Groundwater by Biochars and Activated Carbon
    Xiao, Xin; Ulrich, Bridget A.; Chen, Baoliang; Higgins, Christopher P.
    Environmental Science & Technology (2017), 51 (11), 6342-6351CODEN: ESTHAG; ISSN:0013-936X. (American Chemical Society)
    Despite growing concerns about human exposure to perfluorooctanoate (PFOA) and perfluorooctanesulfonate (PFOS), other poly- and perfluoroalkyl substances (PFASs) derived from aq. film-forming foams (AFFFs) have garnered little attention. While these other PFASs may also be present in AFFF-impacted drinking water, their removal by conventional drinking-water treatment is poorly understood. This study compared the removal of 30 PFASs, including 13 recently discovered PFASs, from an AFFF-impacted drinking water using carbonaceous sorbents (i.e., granular activated carbon, GAC). The approach combined lab. batch expts. and modeling: batch sorption data were used to det. partition coeffs. (Kd) and calibrate a transport model based on intraparticle diffusion-limited sorption kinetics, which was used to make forward predictions of PFAS breakthrough during GAC adsorption. While strong retention was predicted for PFOS and PFOA, nearly all of the recently discovered polyfluorinated chems. and PFOS-like PFASs detected in the AFFF-impacted drinking water were predicted to break through GAC systems before both PFOS and PFOA. These model breakthrough results were used to evaluate a simplified approach to predicting PFAS removal by GAC using compd.-specific retention times on a C18 column (RTC18). Overall, this study reveals that GAC systems for the treatment of AFFF-impacted sources of water for PFOA and PFOS likely achieve poor removal, when operated only for the treatment of PFOS and PFOA, of many unmonitored PFASs of unknown toxicity.
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  9. 9
    McCleaf, P.; Englund, S.; Östlund, A.; Lindegren, K.; Wiberg, K.; Ahrens, L. Removal efficiency of multiple poly- and perfluoroalkyl substances (PFASs) in drinking water using granular activated carbon (GAC) and anion exchange (AE) column tests. Water Res. 2017, 120, 77– 87,  DOI: 10.1016/j.watres.2017.04.057
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    9
    Removal efficiency of multiple poly- and perfluoroalkyl substances (PFASs) in drinking water using granular activated carbon (GAC) and anion exchange (AE) column tests
    McCleaf, Philip; Englund, Sophie; Oestlund, Anna; Lindegren, Klara; Wiberg, Karin; Ahrens, Lutz
    Water Research (2017), 120 (), 77-87CODEN: WATRAG; ISSN:0043-1354. (Elsevier Ltd.)
    Poly- and perfluoroalkyl substances (PFASs) have been detected in drinking water at relatively high concns. throughout the world which has led to implementation of regulatory guidelines for specific PFASs in drinking water in several European countries and in the U.S. The Swedish National Food Agency has detd. that the drinking water of over one third of the country's municipal consumers is at risk or already affected by PFAS contamination. The present study investigated the effects of perfluorocarbon chain length, functional group and isomer structure (branched or linear) on removal of multiple PFASs using granular activated carbon (GAC, Filtrasorb 400) and anion exchange (AE, Purolite A600) column expts. The removal of 14 different PFASs, i.e. the C3-C11, C14 perfluoroalkyl carboxylic acids (PFCAs) (PFBA, PFPeA, PFHxA, PFHpA, PFOA, PFNA, PFDA, PFUnDA, PFDoDA, PFTeDA), perfluorooctane sulfonamide (FOSA), and the C4, C6, C8 perfluoroalkyl sulfonic acids (PFSAs) (PFBS, PFHxS, PFOS), was monitored for a 217 day period. The results indicate the selective nature of PFAS removal as the absorbents are loaded with PFASs and dissolved org. carbon (DOC). A clear relationship between perfluorocarbon chain length and removal efficiency of PFASs using GAC and AE was found while PFASs with sulfonate functional groups displayed greater removal efficiency than those with carboxylate groups. Similarly, time to column breakthrough increased with increasing perfluorocarbon chain length and was greater for the PFSAs than the PFCAs for both GAC and AE. Shorter carbon chained PFASs such as PFBA, PFPeA, PFHxA showed desorption behavior and long-chained PFASs showed increased removal towards the end of the expt. indicating agglomeration or micelle development. Linear isomers of PFOS, PFHxS, and perfluorooctane sulfonamide (FOSA) had greater column removal efficiencies using GAC (and also for AE at greater bed vol. throughput) than the branched and this difference increased at greater bed vol. throughputs. The GAC and AE columns showed a poor correlation between DOC and PFAS removal efficiency. The results indicate that designers and operators of AE and GAC treatment processes must take into consideration the selective nature of PFAS removal and assocd. desorption of short-chain PFCAs during co-removal of multiple PFASs.
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  10. 10
    Fang, Y.; Ellis, A.; Choi, Y. J.; Boyer, T. H.; Higgins, C. P.; Schaefer, C. E.; Strathmann, T. J. Removal of per-and polyfluoroalkyl substances (PFASs) in aqueous film-forming foam (AFFF) using ion-exchange and nonionic resins. Environ. Sci. Technol. 2021, 55, 5001– 5011,  DOI: 10.1021/acs.est.1c00769
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    10
    Removal of per- and polyfluoroalkyl substances (PFASs) in aqueous film-forming foam (AFFF) using ion-exchange and nonionic resins
    Fang, Yida; Ellis, Anderson; Choi, Youn Jeong; Boyer, Treavor H.; Higgins, Christopher P.; Schaefer, Charles E.; Strathmann, Timothy J.
    Environmental Science & Technology (2021), 55 (8), 5001-5011CODEN: ESTHAG; ISSN:0013-936X. (American Chemical Society)
    Despite benefits to the firefighting industry, the release of per- and polyfluoroalkyl substances (PFASs) from aq. film-forming foam (AFFF) into aquatic systems poses significant risks to human health and other organisms. While anion-exchange technologies have proven to be effective for removing perfluoroalkyl acids (PFAAs) from water, their effectiveness for removing the diverse PFAS structures discovered in AFFF remains unknown. Here, we report on the adsorption of 75 PFASs, including 63 polyfluorinated substances, in a dild. AFFF mixt. using 14 com. available ion-exchange (IX)/nonionic resins and granular activated carbon (GAC). Results showed that anion-exchange resins (AERs) exhibited significant adsorption of PFASs compared to cation-exchange resins (CERs), nonionic resins (NIRs), and GAC regardless of the PFAS's predicted charge. Isotherm data showed that macroporous AERs have a higher PFAS adsorption capacity compared to gel-type AERs. Cross-correlation comparison of PFAS/Cl- selectivity coeffs. (Kex) for each PFAS-AER combination showed that the hydrophobicity of the AER functional group, and polymer matrix played a dominant role in detg. resin affinity for PFASs. PFAS structural characteristics also significantly affected adsorption, with increasing chain length and a net neg. charge increasing the extent of adsorption. Results from this study provide guidelines for the selection of resins to adsorb a wider range of PFASs and meaningful insights for the development of quant. models for IX treatment of AFFF-impacted water.
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  11. 11
    Liu, Y.-L.; Sun, M. Ion exchange removal and resin regeneration to treat per- and polyfluoroalkyl ether acids and other emerging PFAS in drinking water. Water Res. 2021, 207, 117781,  DOI: 10.1016/j.watres.2021.117781
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    11
    Ion exchange removal and resin regeneration to treat per- and polyfluoroalkyl ether acids and other emerging PFAS in drinking water
    Liu, Yen-Ling; Sun, Mei
    Water Research (2021), 207 (), 117781CODEN: WATRAG; ISSN:0043-1354. (Elsevier Ltd.)
    Ion exchange (IX) is a promising technol. to remove legacy anionic per- and polyfluoroalkyl substances (PFAS) from water. As increasing nos. of per- and polyfluoroalkyl ether acids (PFEA) and other emerging PFAS were detected in the environment, it is necessary to understand how well IX resins remove these emerging PFAS for drinking water treatment. In this study, nine com. available IX resins were tested to treat a drinking water source spiked with 40 legacy and emerging PFAS at 600 ng/L, including PFEA, perfluoroalkyl carboxylic and sulfonic acids, fluorotelomer sulfonic acids, perfluoroalkane sulfonamides, perfluoroalkane sulfonamidoacetic acids, and zwitterionic species. With limited contact time (15 min), PFAS properties such as the fluorinated chain length, charge, and functional groups all affected PFAS adsorption to resins. However, the impact of PFAS properties on PFAS removal became less pronounced when the contact time increased beyond 2 h, while the resin polymer matrix became the crit. factor for PFAS removal. All five tested polystyrene-divinylbenzene (PS-DVB) resins achieved more than 90% removal in 24 h of 35 PFAS compds., while polymethacrylate and polyacrylic resins achieved >90% removal for less than half of the compds. Regenerating PS-DVB resin was investigated using different salt species, regenerant pH, brine concns., and methanol contents. Sodium chloride and ammonium chloride were found the best brines for regenerating the tested resins. Increasing brine concns. enhanced the regeneration efficiency, esp. for short-chain PFAS. Using simple salt regenerants, up to 94% of selected short-chain PFAS was released from resins designed for general water treatment, but no meaningful regeneration was achieved for long-chain PFAS or PFAS-specific resins when the org. solvent content was less than 20%.
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  12. 12
    Steinle-Darling, E.; Reinhard, M. Nanofiltration for trace organic contaminant removal: Structure, solution, and membrane fouling effects on the rejection of perfluorochemicals. Environ. Sci. Technol. 2008, 42, 5292– 5297,  DOI: 10.1021/es703207s
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    12
    Nanofiltration for Trace Organic Contaminant Removal: Structure, Solution, and Membrane Fouling Effects on the Rejection of Perfluorochemicals
    Steinle-Darling, Eva; Reinhard, Martin
    Environmental Science & Technology (2008), 42 (14), 5292-5297CODEN: ESTHAG; ISSN:0013-936X. (American Chemical Society)
    The use of nanofiltration (NF) membranes for water recycling requires an improved understanding of the factors that govern rejection of potentially harmful org. trace contaminants. Rejections of 15 perfluorochems. (PFCs), 5 perfluorinated sulfonates, 9 perfluorinated carboxylates, and perfluorooctane sulfonamide (FOSA) by 4 nanofiltration membranes (NF270, NF200, DK, and DL) were measured. Rejections for anionic species were >95% for MW >300 g/mol. FOSA (MW =499 g/mol), which is uncharged at the pH of deionized water (5.6), was rejected as little as 42% (DL membrane). Decreasing the pH to <3 decreases rejection by ≤35%, effectively increasing the MWCO of NF270 by >200 g/mol, while a 2500 mg/L NaCl equiv. increase in ionic strength reduces rejections <1%. An alginate fouling layer increases transmission, where quantifiable, by factors of 4-8. Accumulation of PFCs on membranes was measured after the completion of rejection expts. Based on rejection kinetics and the extent of sorption, we infer that 2 different sorption processes are significant: charged species adsorb quickly to the membrane surface, whereas the uncharged FOSA absorbs within the membrane matrix in a much slower process.
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  13. 13
    Appleman, T. D.; Higgins, C. P.; Quiñones, O.; Vanderford, B. J.; Kolstad, C.; Zeigler-Holady, J. C.; Dickenson, E. R. V. Treatment of poly- and perfluoroalkyl substances in US full-scale water treatment systems. Water Res. 2014, 51, 246– 255,  DOI: 10.1016/j.watres.2013.10.067
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    13
    Treatment of poly- and perfluoroalkyl substances in U.S. full-scale water treatment systems
    Appleman, Timothy D.; Higgins, Christopher P.; Quinones, Oscar; Vanderford, Brett J.; Kolstad, Chad; Zeigler-Holady, Janie C.; Dickenson, Eric R. V.
    Water Research (2014), 51 (), 246-255CODEN: WATRAG; ISSN:0043-1354. (Elsevier Ltd.)
    The near ubiquitous presence of poly- and perfluoroalkyl substances (PFASs) in humans has raised concerns about potential human health effects from these chems., some of which are both extremely persistent and bioaccumulative. Because some of these chems. are highly water sol., one major pathway for human exposure is the consumption of contaminated drinking water. This study measured concns. of PFASs in 18 raw drinking water sources and 2 treated wastewater effluents and evaluated 15 full-scale treatment systems for the attenuation of PFASs in water treatment utilities throughout the U.S. A liq.-chromatog. tandem mass-spectrometry method was used to enable measurement of a suite of 23 PFASs, including perfluorocarboxylic acids (PFCAs) and perfluorosulfonic acids (PFSAs). Despite the differences in reporting levels, the PFASs that were detected in >70% of the source water samples (n = 39) included PFSAs, perfluorobutane sulfonic acid (74%), perfluorohexane sulfonic acid (79%), and perfluorooctane sulfonic acid (84%), and PFCAs, perfluoropentanoic acid (74%), perfluorohexanoic acid (79%), perfluoroheptanoic acid (74%), and perfluorooctanoic acid (74%). More importantly, water treatment techniques such as ferric or alum coagulation, granular/micro-/ultra- filtration, aeration, oxidn. (i.e., permanganate, UV/hydrogen peroxide), and disinfection (i.e., ozonation, chlorine dioxide, chlorination, and chloramination) were mostly ineffective in removing PFASs. However, anion exchange and granular activated carbon treatment preferably removed longer-chain PFASs and the PFSAs compared to the PFCAs, and reverse osmosis demonstrated significant removal for all the PFASs, including the smallest PFAS, perfluorobutanoic acid.
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  14. 14
    Sonmez Baghirzade, B.; Zhang, Y.; Reuther, J. F.; Saleh, N. B.; Venkatesan, A. K.; Apul, O. G. Thermal regeneration of spent granular activated carbon presents an opportunity to break the forever PFAS cycle. Environ. Sci. Technol. 2021, 55, 5608– 5619,  DOI: 10.1021/acs.est.0c08224
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    14
    Thermal regeneration of spent granular activated carbon presents an opportunity to break the forever PFAS cycle
    Sonmez Baghirzade, Busra; Zhang, Yi; Reuther, James F.; Saleh, Navid B.; Venkatesan, Arjun K.; Apul, Onur G.
    Environmental Science & Technology (2021), 55 (9), 5608-5619CODEN: ESTHAG; ISSN:0013-936X. (American Chemical Society)
    A review. Extensive use of per- and polyfluoroalkyl substances (PFAS) has caused their ubiquitous presence in natural waters. One of the std. practices for PFAS removal from water is adsorption onto granular activated carbon (GAC); however, this approach generates a new waste stream, i.e., PFAS-laden GAC. Considering the recalcitrance of PFAS mols. in the environment, inadequate disposal (e.g., landfill or incineration) of PFAS-laden GAC may let PFAS back into the aquatic cycle. Therefore, developing approaches for PFAS-laden GAC management present unique opportunities to break its forever circulation within the aq. environment. This comprehensive review evaluates the past two decades of research on conventional thermal regeneration of GAC and critically analyzes and summarizes the literature on regeneration of PFAS-laden GACs. Optimized thermal regeneration of PFAS-laden GACs may provide an opportunity to employ existing regeneration infrastructure to mineralize the adsorbed PFAS and recover the spent GAC. The specific objectives of this review are to investigate the role of physicochem. properties of PFAS on thermal regeneration, to assess the changes in regeneration yield as well as GAC phys. and chem. structure upon thermal regeneration, and to critically discuss regeneration parameters controlling the process. This literature review on the engineered regeneration process illustrates the significant promise of this approach that can break the endless environmental cycle of these forever chems., while preserving the desired physicochem. properties of the valuable GAC adsorbent.
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  15. 15
    Liu, S.; Zhao, S.; Liang, Z.; Wang, F.; Sun, F.; Chen, D. Perfluoroalkyl substances (PFASs) in leachate, fly ash, and bottom ash from waste incineration plants: Implications for the environmental release of PFAS. Sci. Total Environ. 2021, 795, 148468,  DOI: 10.1016/j.scitotenv.2021.148468
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    15
    Perfluoroalkyl substances (PFASs) in leachate, fly ash, and bottom ash from waste incineration plants: Implications for the environmental release of PFAS
    Liu, Shanshan; Zhao, Shiyi; Liang, Zhihong; Wang, Fei; Sun, Feiyun; Chen, Da
    Science of the Total Environment (2021), 795 (), 148468CODEN: STENDL; ISSN:0048-9697. (Elsevier B.V.)
    Perfluoroalkyl substances (PFASs) are a family of chems. widely distributed in daily use consumer products. Most of these products become municipal solid wastes (MSWs) after they have been used. In the present study, we examd. different types of PFASs in leachate, fly ash and bottom ash produced from three MSW incineration plants in southern China. High PFAS levels were found in leachate (mean concn. 215 ng/mL, range 21.4-682 ng/mL) from the incineration plants, which indicated large amts. of PFASs in the wastes leached out. The av. quantities of PFASs annually discharged from the leachates of the three plants were estd. to be approx. 384 kg (Plant A), 47.3 kg (Plant B), and 2.82 kg (Plant C). Relatively lower levels of PFASs in fly ash (mean 16.4 ng/g, range 1.46-87.6 ng/g) and bottom ash (mean 14.6 ng/g, range 3.11-77.4 ng/g) indicated that high-temp. incineration destroyed most of the PFASs. The wide array of PFASs concns. in all three matrixes illustrated that some PFASs-contg. industrial wastes were still entered into local MSW. In general, short chain PFASs, including perfluorobutyric acid (PFBA) and perfluorobutane sulfonate (PFBS), were the primary PFASs in leachate samples. In addn., PFOS was the predominant PFASs in fly ash samples. The results showed that leachate, fly ash, and bottom ash from MSW incineration plants are important vectors of PFASs.
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    Singh, R. K.; Multari, N.; Nau-Hix, C.; Woodard, S.; Nickelsen, M.; Mededovic Thagard, S.; Holsen, T. M. Removal of poly- and per-fluorinated compounds from ion exchange regenerant still bottom samples in a plasma reactor. Environ. Sci. Technol. 2020, 54, 13973– 13980,  DOI: 10.1021/acs.est.0c02158
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    16
    Removal of poly- and per-fluorinated compounds from ion exchange regenerant still bottom samples in a plasma reactor
    Singh, Raj Kamal; Multari, Nicholas; Nau-Hix, Chase; Woodard, Steven; Nickelsen, Michael; Mededovic Thagard, Selma; Holsen, Thomas M.
    Environmental Science & Technology (2020), 54 (21), 13973-13980CODEN: ESTHAG; ISSN:0013-936X. (American Chemical Society)
    "High-concn." and "low-concn." bench-scale batch plasma reactors were used to effectively degrade per- and polyfluoroalkyl substances (PFAS) at a high concn. (~ 100 mg/L) and a low concn. (<1μg/L), resp., in ion exchange (IX) regenerant still bottom (SB) solns. In the SBs, numerous PFAS were detected with a wide concn. range (~ 0.01 to 100 mg/L; total oxidizable precursors (TOP) ~ 4000 to 10000 mg/L). In the "high-concn." plasma reactor, the concns. of PFAS precursors and long-chain perfluoroalkyl acids (PFAAs) (≥6C for PFSAs and ≥8C for perfluorocarboxylic acids (PFCAs)) were decreased by >99.9% in 2 h, and short-chain PFAAs (<6C for perfluorocarboxylic acids (PFSAs) and <8C PFCAs) were decreased by >99% in 6 h of treatment. Subsequently, a "low concn." plasma reactor was used to remove addnl. PFAAs. In this reactor, the addn. of CTAB (cetrimonium bromide, a cationic surfactant) caused short-chain PFAAs, other than PFBA, to be removed to below detection limits in 90 min of treatment time. Overall, >99% of the TOP present in SBs was removed during the treatment. Fluorine recovery of 47 to 117% was obtained in six SB samples. Energy requirement (EE/O) for the treatment of PFOA and PFOS from SBs ranged from 380 to 830 kWh/m3.
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  17. 17
    Qanbarzadeh, M.; Wang, D.; Ateia, M.; Sahu, S. P.; Cates, E. L. Impacts of reactor configuration, degradation mechanisms, and water matrices on perfluorocarboxylic acid treatment efficiency by the UV/Bi3O(OH)(PO4)2 photocatalytic process. ACS ES&T Engg 2021, 1, 239– 248,  DOI: 10.1021/acsestengg.0c00086
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    Zhu, Y.; Xu, T.; Zhao, D.; Li, F.; Liu, W.; Wang, B.; An, B. Adsorption and solid-phase photocatalytic degradation of perfluorooctane sulfonate in water using gallium-doped carbon-modified titanate nanotubes. Chem. Eng. J. 2021, 421, 129676,  DOI: 10.1016/j.cej.2021.129676
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    18
    Adsorption and solid-phase photocatalytic degradation of perfluorooctane sulfonate in water using gallium-doped carbon-modified titanate nanotubes
    Zhu, Yangmo; Xu, Tianyuan; Zhao, Dongye; Li, Fan; Liu, Wen; Wang, Buhua; An, Byungryul
    Chemical Engineering Journal (Amsterdam, Netherlands) (2021), 421 (Part_1), 129676CODEN: CMEJAJ; ISSN:1385-8947. (Elsevier B.V.)
    Perfluorooctane sulfonate (PFOS) has drawn increasing attention due to its omnipresence and adverse health effects. We prepd. a new adsorptive photocatalyst, Ga/TNTs@AC, based on activated carbon and TiO2, and tested the adsorption and subsequent solid-phase photodegrdn. of PFOS. Ga/TNTs@AC showed faster adsorption kinetics and higher affinity for PFOS than the parent AC, and could degrade 75.0% and mineralize 66.2% of pre-sorbed PFOS within 4-h UV irradn. The efficient PFOS photodegrdn. also regenerates Ga/TNTs@AC, allowing for repeated uses without invoking chem. regenerants. The superior photoactivity is attributed to the oxygen vacancies, which not only suppressed recombination of the e-/h+ pairs, but also facilitated O.-2 generation. Both h+ and O.-2 played crit. roles in the PFOS degrdn., which starts with cleavage of the sulfonate group and converts it into PFOA that is then decarboxylated and defluorinated following the stepwise defluorination mechanism. Ga/TNTs@AC holds the potential for more cost-effective PFOS degrdn.
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  19. 19
    Yang, S.; Fernando, S.; Holsen, T. M.; Yang, Y. Inhibition of perchlorate formation during the electrochemical oxidation of perfluoroalkyl acid in groundwater. Environ. Sci. Technol. Lett. 2019, 6, 775– 780,  DOI: 10.1021/acs.estlett.9b00653
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    19
    Inhibition of Perchlorate Formation during the Electrochemical Oxidation of Perfluoroalkyl Acid in Groundwater
    Yang, Shasha; Fernando, Sujan; Holsen, Thomas M.; Yang, Yang
    Environmental Science & Technology Letters (2019), 6 (12), 775-780CODEN: ESTLCU; ISSN:2328-8930. (American Chemical Society)
    Perfluorooctanoic acid (PFOA) and perfluorooctanesulfonate (PFOS) are groundwater contaminants of emerging concern due to their toxicity and persistence. Currently, there are limited destructive treatment options for this type of water. One promising approach is electrochem. oxidn. (EO) using a boron-doped diamond (BDD) anode. However, during EO treatment, chloride in water is readily converted to perchlorate (ClO4-), which is an endocrine disruptor. This is a common dilemma for EO techniques: anodes with higher EO activity tend to produce more ClO4-. In this study, we used the BDD anode as a model anode to treat PFOA and PFOS in a chloride-bearing electrolyte. We found that the formation of ClO4- can be largely inhibited without compromising the efficiency of PFOA and PFOS destruction by adding hydrogen peroxide (≥50 mM H2O2). Exptl. approaches and computational kinetic modeling indicate that H2O2 inhibits ClO4- formation by quenching chlorine and hydroxyl radicals and the oxidn. of PFOA and PFOS is primarily detd. by direct electron transfer oxidn., regardless of the dominant radical species. This facile strategy suppressed 88% of ClO4- formation during EO treatment of groundwater spiked with PFOA and PFOS.
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  20. 20
    Huang, D.; Wang, K.; Niu, J.; Chu, C.; Weon, S.; Zhu, Q.; Lu, J.; Stavitski, E.; Kim, J.-H. Amorphous Pd-loaded Ti4O7 electrode for direct anodic destruction of perfluorooctanoic acid. Environ. Sci. Technol. 2020, 54, 10954– 10963,  DOI: 10.1021/acs.est.0c03800
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    20
    Amorphous Pd-loaded Ti4O7 electrode for direct anodic destruction of perfluorooctanoic acid
    Huang, Dahong; Wang, Kaixuan; Niu, Junfeng; Chu, Chiheng; Weon, Seunghyun; Zhu, Qianhong; Lu, Jianjiang; Stavitski, Eli; Kim, Jae-Hong
    Environmental Science & Technology (2020), 54 (17), 10954-10963CODEN: ESTHAG; ISSN:0013-936X. (American Chemical Society)
    We here present a novel Ti4O7-based electrode loaded with amorphous Pd clusters that achieve efficient anodic destruction of perfluorooctanoic acid (PFOA), a persistent water pollutant with significant environmental and human health concerns. These amorphous Pd clusters were characterized by the disordered, noncryst. arrangement of Pd single atoms in close proximity, in contrast to cryst. Pd nanoparticles that have been often employed to tailor the electronic properties of an electrode. We found that the Ti4O7 electrode loaded with amorphous Pd clusters significantly outperformed the Ti4O7 electrode loaded with cryst. Pd particles due to enhanced electron transfer through dominant Pd-O bonds. Combined with the efficient binding of PFOA and its degrdn. intermediates to the fluorinated electrode surface, this electrode was capable of mineralizing PFOA and releasing fluoride as F-. The reaction pathway was found to proceed without involving reactive oxygen species and therefore was not quenched by common anions in complex natural water systems such as chloride ions.
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  21. 21
    Lewis, A. J.; Joyce, T.; Hadaya, M.; Ebrahimi, F.; Dragiev, I.; Giardetti, N.; Yang, J.; Fridman, G.; Rabinovich, A.; Fridman, A. A.; McKenzie, E. R.; Sales, C. M. Rapid degradation of PFAS in aqueous solutions by reverse vortex flow gliding arc plasma. Environ. Sci.: Water Res. Technol. 2020, 6, 1044– 1057,  DOI: 10.1039/c9ew01050e
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    21
    Rapid degradation of PFAS in aqueous solutions by reverse vortex flow gliding arc plasma
    Lewis, Asa J.; Joyce, Thomas; Hadaya, Maher; Ebrahimi, Farshad; Dragiev, Ivan; Giardetti, Nickolas; Yang, Junchun; Fridman, Gregory; Rabinovich, Alexander; Fridman, Alexander A.; McKenzie, Erica R.; Sales, Christopher M.
    Environmental Science: Water Research & Technology (2020), 6 (4), 1044-1057CODEN: ESWRAR; ISSN:2053-1419. (Royal Society of Chemistry)
    Poly and perfluoroalkyl substances (PFAS) are a group of fluorinated org. anthropogenic chems. that are resistant to degrdn. In this paper, non-equil., reverse vortex gliding arc plasma (GAP) discharges in air, nitrogen (N2), and pure oxygen (O2) gases were investigated for the removal of perfluoroalkyl carboxylates (PFCA), perfluoroalkyl sulfonates (PFSA), and fluorotelomer sulfonates (FtS) from liq. solns. in a 1-L treatment system. At initial concns. ranging from 0.05 g L-1 to 1 g L-1 significant removal was obsd. for all PFAS compds. by GAP discharges in air, but the degree of degrdn. and defluorination was highly dependent on perfluorinated alkyl chain lengths, with all those contg. 8 or more perfluorinated carbons achieving greater than 90% removal and often greater than 25% defluorination in one hour of treatment time. Following treatment, a fluorine mass balance was attempted for PFOS (58.3% recovery) and PFOA (98.2% recovery) where only a miniscule portion (5.6% and 4.2%) resp. of the degraded PFOS and PFOA were converted to quantifiable PFAS, while the rest of the fluorine may leave as gaseous species or non-quantifiable PFAS. The non-equil. GAP discharge used in this study was found to use similar amts. of energy to other studies using non-equil. plasma (150 kJ L-1 to 1000 kJ L-1), which is approx. three to twenty times less than the amt. of energy used to evap. water (∼3000 kJ L-1). Assuming pseudo-first-order kinetics, the figure-of-merit elec. energy per order (EEo) values were calcd. to est. the energy efficiency of the system. The lowest EEo for PFOS was 23.2 kW h m-3 per order and 213.4 kW h m-3 per order for PFOA, similar with existing technologies (which range from 10 to 10 000 kW h m-3 per order). These results indicate that non-thermal air plasma discharges are promising technologies for treatment of PFAS that should be further researched and developed.
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  22. 22
    Saleem, M.; Biondo, O.; Sretenović, G.; Tomei, G.; Magarotto, M.; Pavarin, D.; Marotta, E.; Paradisi, C. Comparative performance assessment of plasma reactors for the treatment of PFOA; reactor design, kinetics, mineralization and energy yield. Chem. Eng. J. 2020, 382, 123031,  DOI: 10.1016/j.cej.2019.123031
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    22
    Comparative performance assessment of plasma reactors for the treatment of PFOA; reactor design, kinetics, mineralization and energy yield
    Saleem, Mubbshir; Biondo, Omar; Sretenovic, Goran; Tomei, Giulia; Magarotto, Mirko; Pavarin, Daniele; Marotta, Ester; Paradisi, Cristina
    Chemical Engineering Journal (Amsterdam, Netherlands) (2020), 382 (), 123031CODEN: CMEJAJ; ISSN:1385-8947. (Elsevier B.V.)
    The development of efficient plasma-based technologies for water treatment in general and decontamination from perfluoroalkyl substances, in particular, is a timely and challenging research topic. This study investigated the degrdn. of PFOA (perfluorooctanoic acid) in water using three reactors with different configurations and implementing different plasma regimes. Two reactors were available from previous studies on other recalcitrant pollutants and use, resp., corona discharge and plasma in gas bubbles. The third reactor was designed and developed for this specific application and uses a self-pulsing streamer discharge (SPD) over the liq. surface. The performance of the three reactors was assessed and compared using air as plasma feed gas and a PFOA soln. (41.4 mg/L) in Milli-Q-water. The SPD reactor was found to be the most efficient in terms of energy efficiency and PFOA conversion and degrdn. rate. It was therefore further tested and characterized by studying the effects of changing the aq. media in which PFOA was dissolved (Milli-Q and tap water) and the plasma feed gas (synthetic air, ambient air and argon). Due to the formation of nitrous and nitric acids, esp. for plasma generated in ambient and synthetic air, the soln. pH, cond., and hence the plasma input power changed significantly during the expts. The best results were obtained using argon for plasma inception and PFOA solns. in tap water: the energy efficiency and fluoride recovery were 561 mg/kWh and 47%, resp.
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  23. 23
    Singh, R. K.; Brown, E.; Thagard, S. M.; Holsen, T. M. Treatment of PFAS-containing landfill leachate using an enhanced contact plasma reactor. J. Hazard. Mater. 2021, 408, 124452,  DOI: 10.1016/j.jhazmat.2020.124452
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    23
    Treatment of PFAS-containing landfill leachate using an enhanced contact plasma reactor
    Singh, Raj Kamal; Brown, Elizabeth; Mededovic Thagard, Selma; Holsen, Thomas M.
    Journal of Hazardous Materials (2021), 408 (), 124452CODEN: JHMAD9; ISSN:0304-3894. (Elsevier B.V.)
    A bench-scale plasma reactor was used to degrade poly- and perfluoroalkyl substances (PFAS) in landfill leachate samples obtained from three different locations. In the leachate samples before treatment, five long-chain, six short-chain perfluoroalkyl acids (PFAAs) and eight PFAA precursors were detected in a wide concn. range (∼102 to 105 ng/L; total oxidizable precursors (TOP) ∼106 ng/L). The concn. of perfluorooctane sulfonate (PFOS) plus perfluorooctanoic acid (PFOA) ranged between 2000 and 3000 ng/L. Plasma-based water treatment of 500 mL samples resulted in faster removal rates for longer-chain than shorter chain length PFAAs. Both PFOS and PFOA were removed to below United States Environmental Protection Agency's (USEPA's) health advisory concn. level (HAL) concns. (<70 ng/L) in 10-75 min; 90% PFOA and PFOS removal was achieved in 10 min. Long-chain and short-chain PFAAs were removed by >99.9% and 10-99.9%, resp. The removal rate const. (kPFOA+PFOS) for combined PFOA and PFOS ranged between 0.20 and 0.34 min-1. Overall, 60 ± 2% of the TOP concn. and 34 ± 2% of the TOC were removed. No effect of non-PFAS co-contaminants (e.g., total initial org. carbon concn. ∼2000 mg/L) on the degrdn. efficiency was obsd. Short-chain PFAA removal efficacy was enhanced by adding a cationic surfactant (cetrimonium bromide). Overall, the results indicate that plasma-based technol. may be a viable technol. for the treatment of PFAS-contaminated landfill leachates.
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  24. 24
    Huang, L.; Dong, W.; Hou, H. Investigation of the reactivity of hydrated electron toward perfluorinated carboxylates by laser flash photolysis. Chem. Phys. Lett. 2007, 436, 124– 128,  DOI: 10.1016/j.cplett.2007.01.037
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    24
    Investigation of the reactivity of hydrated electron toward perfluorinated carboxylates by laser flash photolysis
    Huang, Li; Dong, Wenbo; Hou, Huiqi
    Chemical Physics Letters (2007), 436 (1-3), 124-128CODEN: CHPLBC; ISSN:0009-2614. (Elsevier B.V.)
    Laser flash photolysis technique was employed to investigate the reactivity of hydrated electron (e-aq) toward a series of perfluorinated carboxylates, CnF2n+1COO- (n = 1, 3, 7), at 288 ± 1 K in aq. phase. It was demonstrated that the length of -CnF2n+1 group exerted substantial influence on the rate const. The second-order rate consts. for e-aq with CF3COO-, C3F7COO-, C7F15COO- were estd. to be (1.9 ± 0.2) × 106 M-1 s-1 (μ = 0), (7.1 ± 0.3) × 106 M-1 s-1 (μ = 0) and (1.7 ± 0.5) × 107 M-1 s-1 (μ = 0.01 M), resp.
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    Park, H.; Vecitis, C. D.; Cheng, J.; Choi, W.; Mader, B. T.; Hoffmann, M. R. Reductive defluorination of aqueous perfluorinated alkyl surfactants: Effects of ionic headgroup and chain length. J. Phys. Chem. A 2009, 113, 690– 696,  DOI: 10.1021/jp807116q
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    25
    Reductive Defluorination of Aqueous Perfluorinated Alkyl Surfactants: Effects of Ionic Headgroup and Chain Length
    Park, Hyunwoong; Vecitis, Chad D.; Cheng, Jie; Choi, Wonyong; Mader, Brian T.; Hoffmann, Michael R.
    Journal of Physical Chemistry A (2009), 113 (4), 690-696CODEN: JPCAFH; ISSN:1089-5639. (American Chemical Society)
    Perfluorinated chems. (PFCs) are distributed throughout the environment. In the case of perfluorinated alkyl carboxylates and sulfonates, they can be classified as persistent org. pollutants since they are resistant to environmentally relevant redn., oxidn., and hydrolytic processes. With this in mind, we report on the reductive defluorination of perfluorobutanoate, PFBA (C3F7CO2-), perfluorohexanoate, PFHA (C5F11CO2-), perfluorooctanoate, PFOA (C7F15CO2-), perfluorobutane sulfonate, PFBS (C4F9SO3-), perfluorohexane sulfonate, PFHS (C6F13SO3-), and perfluorooctane sulfonate, PFOS (C8F17SO3-) by aquated electrons, eaq-, that are generated from the UV photolysis (λ = 254 nm) of iodide. The ionic headgroup (-SO3- vs -CO2-) has a significant effect on the redn. kinetics and extent of defluorination (F index = -[F-]produced/[PFC]degraded). Perfluoroalkylsulfonate redn. kinetics and the F index increase linearly with increasing chain length. In contrast, perfluoroalkylcarboxylate chain length appears to have a negligible effect on the obsd. kinetics and the F index. H/F ratios in the gaseous fluoro-org. products are consistent with measured F indexes. Incomplete defluorination of the gaseous products suggests a reductive cleavage of the ionic headgroup occurs before complete defluorination. Detailed mechanisms involving initiation by aquated electrons are proposed.
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    Song, Z.; Tang, H.; Wang, N.; Zhu, L. Reductive defluorination of perfluorooctanoic acid by hydrated electrons in a sulfite-mediated UV photochemical system. J. Hazard. Mater. 2013, 262, 332– 338,  DOI: 10.1016/j.jhazmat.2013.08.059
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    26
    Reductive defluorination of perfluorooctanoic acid by hydrated electrons in a sulfite-mediated UV photochemical system
    Song, Zhou; Tang, Heqing; Wang, Nan; Zhu, Lihua
    Journal of Hazardous Materials (2013), 262 (), 332-338CODEN: JHMAD9; ISSN:0304-3894. (Elsevier B.V.)
    A method for reductive degrdn. of perfluorooctanoic acid (PFOA) was established by using a sulfite/UV process. This process led to a PFOA removal of 100% at ∼1 h and a defluorination ratio of 88.5% at reaction time of 24 h under N2 atmosphere, whereas the use of either UV irradn. or SO32- alone induced little defluorination of PFOA under the same conditions. The reductive defluorination of PFOA was achieved by hydrated electrons being generated from the photo-conversion of SO32- as a mediator. Theor. reaction kinetic anal. demonstrated that the generation of hydrated electrons was promoted by increasing either SO32- concn. or soln. pH, leading to the acceleration of the PFOA defluorination. Accompanying the redn. of PFOA, a small amt. of short-chain perfluorocarboxylic acids, less fluorinated carboxylic acids and perfluorinated alkyl sulfonates were generated, all of which were able to be further degraded with further releasing of F- ions. Based on the generation, accumulation and distribution of intermediates, hydrated electrons induced defluorination pathway of PFOA was proposed in a sulfite-mediated UV photochem. system.
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  27. 27
    Tian, H.; Gao, J.; Li, H.; Boyd, S. A.; Gu, C. Complete defluorination of perfluorinated compounds by hydrated electrons generated from 3-indole-acetic-acid in organomodified montmorillonite. Sci. Rep. 2016, 6, 32949,  DOI: 10.1038/srep32949
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    27
    Complete Defluorination of Perfluorinated Compounds by Hydrated Electrons Generated from 3-Indole-acetic-acid in Organomodified Montmorillonite
    Tian, Haoting; Gao, Juan; Li, Hui; Boyd, Stephen A.; Gu, Cheng
    Scientific Reports (2016), 6 (), 32949CODEN: SRCEC3; ISSN:2045-2322. (Nature Publishing Group)
    Here we describe a unique process that achieves complete defluorination and decompn. of perfluorinated compds. (PFCs) which comprise one of the most recalcitrant and widely distributed classes of toxic pollutant chems. found in natural environments. Photogenerated hydrated electrons derived from 3-indole-acetic-acid within an organomodified clay induce the reductive defluorination of co-sorbed PFCs. The process proceeds to completion within a few hours under mild reaction conditions. The organomontmorillonite clay promotes the formation of highly reactive hydrated electrons by stabilizing indole radical cations formed upon photolysis, and prevents their deactivation by reaction with protons or oxygen. In the constrained interlayer regions of the clay, hydrated electrons and co-sorbed PFCs are brought in close proximity thereby increasing the probability of reaction. This novel green chem. provides the basis for in situ and ex situ technologies to treat one of the most troublesome, recalcitrant and ubiquitous classes of environmental contaminants, i.e., PFCs, utilizing innocuous reagents, naturally occurring materials and mild reaction conditions.
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  28. 28
    Sun, Z.; Zhang, C.; Xing, L.; Zhou, Q.; Dong, W.; Hoffmann, M. R. UV/nitrilotriacetic acid process as a novel strategy for efficient photoreductive degradation of perfluorooctanesulfonate. Environ. Sci. Technol. 2018, 52, 2953– 2962,  DOI: 10.1021/acs.est.7b05912
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    28
    UV/nitrilotriacetic acid process as a novel strategy for efficient photoreductive degradation of perfluorooctanesulfonate
    Sun, Zhuyu; Zhang, Chaojie; Xing, Lu; Zhou, Qi; Dong, Wenbo; Hoffmann, Michael R.
    Environmental Science & Technology (2018), 52 (5), 2953-2962CODEN: ESTHAG; ISSN:0013-936X. (American Chemical Society)
    Perfluorooctanesulfonate (PFOS) is a toxic, bioaccumulative, and highly persistent anthropogenic chem. Hydrated electrons (eaq-) are potent nucleophiles that can effectively decomp. PFOS. In previous studies, eaq- are mainly produced by photoionization of aq. anions or arom. compds. In this study, we proposed a new photolytic strategy to generate eaq- and in turn decomp. PFOS, which utilizes nitrilotriacetic acid (NTA) as a photosensitizer to induce water photodissocn. and photoionization, and subsequently as a scavenger of hydroxyl radical (•OH) to minimize the geminate recombination between •OH and eaq-. The net effect is to increase the amt. of eaq- available for PFOS degrdn. The UV/NTA process achieved a high PFOS degrdn. ratio of 85.4% and a defluorination ratio of 46.8% within 10 h. A pseudo-first-order rate const. (k) of 0.27 h-1 was obtained. The laser flash photolysis study indicates that eaq- is the dominant reactive species responsible for PFOS decompn. The generation of eaq- is greatly enhanced and its half-life is significantly prolonged in the presence of NTA. The ESR measurement verified the photodissocn. of water by detecting •OH. The model compd. study indicates that the acetate and amine groups are the primary reactive sites.
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    Bentel, M. J.; Yu, Y.; Xu, L.; Li, Z.; Wong, B. M.; Men, Y.; Liu, J. Defluorination of per- and polyfluoroalkyl substances (PFASs) with hydrated electrons: Structural dependence and implications to PFAS remediation and management. Environ. Sci. Technol. 2019, 53, 3718– 3728,  DOI: 10.1021/acs.est.8b06648
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    29
    Defluorination of Per- and Polyfluoroalkyl Substances (PFASs) with Hydrated Electrons: Structural Dependence and Implications to PFAS Remediation and Management
    Bentel, Michael J.; Yu, Yaochun; Xu, Lihua; Li, Zhong; Wong, Bryan M.; Men, Yujie; Liu, Jinyong
    Environmental Science & Technology (2019), 53 (7), 3718-3728CODEN: ESTHAG; ISSN:0013-936X. (American Chemical Society)
    This study investigates crit. structure-reactivity relationships within 34 representative per- and polyfluoroalkyl substances (PFASs) undergoing defluorination with UV-generated hydrated electrons. While CnF2n+1-COO- with variable fluoroalkyl chain lengths (n = 2 to 10) exhibited a similar rate and extent of parent compd. decay and defluorination, the reactions of telomeric CnF2n+1-CH2CH2-COO- and CnF2n+1-SO3- showed an apparent dependence on the length of the fluoroalkyl chain. Cross comparison of exptl. results, including different rates of decay and defluorination of specific PFAS categories, the incomplete defluorination from most PFAS structures, and the surprising 100% defluorination from CF3COO-, leads to the elucidation of new mechanistic insights into PFAS degrdn. Theor. calcns. on the C-F bond dissocn. energies (BDEs) of all PFAS structures reveal strong relationships among (i) the rate and extent of decay and defluorination, (ii) head functional groups, (iii) fluoroalkyl chain length, and (iv) the position and no. of C-F bonds with low BDEs. These relationships are further supported by the spontaneous cleavage of specific bonds during calcd. geometry optimization of PFAS structures bearing one extra electron, and by the product analyses with high-resoln. mass spectrometry. Multiple reaction pathways, including H/F exchange, dissocn. of terminal functional groups, and decarboxylation-triggered HF elimination and hydrolysis, result in the formation of variable defluorination products. The selectivity and ease of C-F bond cleavage highly depends on mol. structures. These findings provide crit. information for developing PFAS treatment processes and technologies to destruct a wide scope of PFAS pollutants and for designing fluorochem. formulations to avoid releasing recalcitrant PFASs into the environment.
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    Cui, J.; Gao, P.; Deng, Y. Destruction of per- and polyfluoroalkyl substances (PFAS) with advanced reduction processes (ARPs): A critical review. Environ. Sci. Technol. 2020, 54, 3752– 3766,  DOI: 10.1021/acs.est.9b05565
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    30
    Destruction of Per- and Polyfluoroalkyl Substances (PFAS) with Advanced Reduction Processes (ARPs): A Critical Review
    Cui, Junkui; Gao, Panpan; Deng, Yang
    Environmental Science & Technology (2020), 54 (7), 3752-3766CODEN: ESTHAG; ISSN:0013-936X. (American Chemical Society)
    A review. Advanced redn. processes (ARPs) have emerged as a promising method for destruction of persistent per- and polyfluoroalkyl substances (PFAS) in H2O due to the generation of short-lived and highly reductive hydrated electrons (eaq-). This study provides a crit. review on the mechanisms and performance of reductive destruction of PFAS with eaq-. Unique properties of eaq- and its generation in different ARP systems, particularly UV/sulfite and UV/iodide, are overviewed. Different degrdn. mechanisms of PFAS chems., such as perfluorooctanoic acid (PFOA), perfluorooctanesulfonate (PFOS), and others (e.g., short chain perfluorocarboxylic acids (PFCAs) and perfluorosulfonic acids (PFSAs), per- and polyfluoro dicarboxylic acids, and fluorotelomer carboxylic acids), are reviewed, discussed, and compared. The degrdn. pathways of these PFAS chems. rely heavily upon their head groups. For specific PFAS types, fluoroalkyl chain lengths may also affect their reductive degrdn. patterns. Degrdn. and defluorination efficiencies of PFAS are considerably influenced by soln. chem. parameters and operating factors, such as pH, dose of chem. solute (i.e., sulfite or iodide) for eaq- photoprodn., dissolved O, humic acid, nitrate, and temp. Also, implications of the state-of-the-art knowledge on practical PFAS control actions in H2O industries are discussed and the priority research needs are identified.
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    Bao, Y.; Huang, J.; Cagnetta, G.; Yu, G. Removal of F–53B as PFOS alternative in chrome plating wastewater by UV/sulfite reduction. Water Res. 2019, 163, 114907,  DOI: 10.1016/j.watres.2019.114907
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    Removal of F-53B as PFOS alternative in chrome plating wastewater by UV/Sulfite reduction
    Bao, Yixiang; Huang, Jun; Cagnetta, Giovanni; Yu, Gang
    Water Research (2019), 163 (), 114907CODEN: WATRAG; ISSN:0043-1354. (Elsevier Ltd.)
    Chrome mist suppressants are key chems. used in the chrome plating industry to reduce exposure of workers by inhalation to airborne chromic acid pollution. Perfluoroalkyl sulfonated compds. are excellent mist suppressants, thanks to their chem. stability and surface activity. Therefore, despite mounting evidence for their persistence, bioaccumulation and toxicity, it is likely that such chems. will continue to be used for the foreseeable future because of their importance and lack of alternatives. The present study is aimed at assessing the feasibility of advanced redn. as an effective technol. to treat chrome plating industry wastewater. In particular, wastewater contg. a chlorinated polyfluorinated ether sulfonate (i.e. F-53B), an alternative to perfluorooctanesulfonate (PFOS) used to prep. chrome mist suppressant in China, was treated by UV-activated sulfite. Results demonstrates that in ultrapure water F-53B can be easily degraded within 1 min-much faster than PFOS. Stoichiometric fluoride recovery was also achieved, confirming significant defluorination of the pollutant. Such superior reducibility was due to the presence of chlorine atoms, as corroborated by quantum chem. calcns. F-53B degrdn. was also achieved in chrome plating industrial wastewater, which yielded results were slower than those achieved in the lab. nonetheless obtained complete abatement within 60 min. These results suggest that the proposed advanced redn. process is one of the safest options to control PFAS discharge in the environment and reduce the related risks to ecosystems.
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    Bentel, M. J.; Yu, Y.; Xu, L.; Kwon, H.; Li, Z.; Wong, B. M.; Men, Y.; Liu, J. Degradation of perfluoroalkyl ether carboxylic acids with hydrated electrons: Structure-reactivity relationships and environmental implications. Environ. Sci. Technol. 2020, 54, 2489– 2499,  DOI: 10.1021/acs.est.9b05869
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    Degradation of Perfluoroalkyl Ether Carboxylic Acids with Hydrated Electrons: Structure-Reactivity Relationships and Environmental Implications
    Bentel, Michael J.; Yu, Yaochun; Xu, Lihua; Kwon, Hyuna; Li, Zhong; Wong, Bryan M.; Men, Yujie; Liu, Jinyong
    Environmental Science & Technology (2020), 54 (4), 2489-2499CODEN: ESTHAG; ISSN:0013-936X. (American Chemical Society)
    This study explores structure-reactivity relationships for the degrdn. of emerging perfluoroalkyl ether carboxylic acid (PFECA) pollutants with UV-generated hydrated electrons (eaq-). The rate and extent of PFECA degrdn. depend on both the branching extent and the chain length of oxygen-segregated fluoroalkyl moieties. Kinetic measurements, theor. calcns., and transformation product analyses provide a comprehensive understanding of the PFECA degrdn. mechanisms and pathways. In comparison to traditional full-carbon-chain perfluorocarboxylic acids, the distinct degrdn. behavior of PFECAs is attributed to their ether structures. The ether oxygen atoms increase the bond dissocn. energy of the C-F bonds on the adjacent -CF2- moieties. This impact reduces the formation of H/F-exchanged polyfluorinated products that are recalcitrant to reductive defluorination. Instead, the cleavage of ether C-O bonds generates unstable perfluoroalcs. and thus promotes deep defluorination of short fluoroalkyl moieties. In comparison to linear PFECAs, branched PFECAs have a higher tendency of H/F exchange on the tertiary carbon and thus lower percentages of defluorination. These findings provide mechanistic insights for an improved design and efficient degrdn. of fluorochems.
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    Chen, Z.; Li, C.; Gao, J.; Dong, H.; Chen, Y.; Wu, B.; Gu, C. Efficient reductive destruction of perfluoroalkyl substances under self-assembled micelle confinement. Environ. Sci. Technol. 2020, 54, 5178– 5185,  DOI: 10.1021/acs.est.9b06599
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    Efficient Reductive Destruction of Perfluoroalkyl Substances under Self-Assembled Micelle Confinement
    Chen, Zhanghao; Li, Chen; Gao, Juan; Dong, Hailiang; Chen, Yi; Wu, Bing; Gu, Cheng
    Environmental Science & Technology (2020), 54 (8), 5178-5185CODEN: ESTHAG; ISSN:0013-936X. (American Chemical Society)
    Recently, perfluoroalkyl substances (PFASs) have received great attention from both academia and the industry due to their persistence and health risks. Here, we developed a simple ternary self-assembled micelle composite, consisting of a photosensitive substance (indole HOAc, IAA), cationic surfactant (cetyltrimethylammonium bromide), and contaminant (PFAS). Owing to the rapid hydrated electron transfer from IAA to the PFAS in the micelle, the PFAS degrdn. and defluorination were greatly enhanced even under ambient conditions. After 2.5 h UV irradn., the perfluorooctanoic acid (PFOA) concn. decreased from 10 mg L-1 to ∼60 ng L-1, which is below the drinking H2O health advisory level of the United States Environmental Protection Agency for the combined concn. of PFOA and perfluorooctane sulfonate (70 ng L-1). Meanwhile, the dissolved org. C content of the reaction soln. was also reduced to ∼3 mg L-1 due to the quick settlement and automatic sepn. of the micelle. Also, the newly developed composite was also adaptable to a wide pH range (pH 4-8), attributing to the barrier created by the ternary micelle system. This novel self-assembly method is expected to directly treat industrial PFAS-contg. wastewater or PFAS-enriched concs. derived from adsorption processes. The conceptually new advanced redn. technique represents a major breakthrough toward PFAS rapid destruction and efficient usage of hydrated electrons and might also shed light on other environmental applications.
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    Chen, Z.; Teng, Y.; Mi, N.; Jin, X.; Yang, D.; Wang, C.; Wu, B.; Ren, H.; Zeng, G.; Gu, C. Highly efficient hydrated electron utilization and reductive destruction of perfluoroalkyl substances induced by intermolecular interaction. Environ. Sci. Technol. 2021, 55, 3996– 4006,  DOI: 10.1021/acs.est.0c07927
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    Highly efficient hydrated electron utilization and reductive destruction of perfluoroalkyl substances induced by intermolecular interaction
    Chen, Zhanghao; Teng, Ying; Mi, Na; Jin, Xin; Yang, Deshuai; Wang, Chao; Wu, Bing; Ren, Hongqiang; Zeng, Guixiang; Gu, Cheng
    Environmental Science & Technology (2021), 55 (6), 3996-4006CODEN: ESTHAG; ISSN:0013-936X. (American Chemical Society)
    Perfluoroalkyl substances (PFASs) are highly toxic synthetic chems., which are considered the most persistent org. contaminants in the environment. Previous studies have demonstrated that hydrated electron based techniques could completely destruct these compds. However, in the reactions, alk. and anaerobic conditions are generally required or surfactants are involved. Herein, we developed a simple binary composite, only including PFAS and hydrated electron source chem. The system exhibited high efficiency for the utilization of hydrated electrons to decomp. PFASs. By comparing the degrdn. processes of perfluorooctanoic acid (PFOA) in the presence of seven indole derivs. with different chem. properties, we could conclude that the reaction efficiency was dependent on not only the yield of hydrated electrons but also the interaction between PFOA and indole deriv. Among these derivs., indole showed the highest degrdn. performance due to its relatively high ability to generate hydrated electrons, and more importantly, indole could form a hydrogen bonding with PFOA to accelerate the electron transfer. Moreover, the novel composite demonstrated high reaction efficiency even with coexisting humic substance and in a wide pH range (4-10). This study would deepen our understanding of the design of hydrated electron based techniques to treat PFAS-contg. wastewater.
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    Huang, C.; Linkous, C. A.; Adebiyi, O.; T-Raissi, A. Hydrogen production via photolytic oxidation of aqueous sodium sulfite solutions. Environ. Sci. Technol. 2010, 44, 5283– 5288,  DOI: 10.1021/es903766w
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    Hydrogen Production via Photolytic Oxidation of Aqueous Sodium Sulfite Solutions
    Huang, Cunping; Linkous, Clovis A.; Adebiyi, Olawale; T-Raissi, Ali
    Environmental Science & Technology (2010), 44 (13), 5283-5288CODEN: ESTHAG; ISSN:0013-936X. (American Chemical Society)
    Sulfur dioxide (SO2) emission from coal-burning power plants and refinery operations has been implicated as a cause of acid rain and other air pollution related problems. The conventional treatment of SO2-contaminated air consists of two steps: SO2 absorption using an aq. sodium hydroxide soln., forming aq. sodium sulfite (Na2SO3), and Na2SO3 oxidn. via air purging to produce sodium sulfate (Na2SO4). In this process, the potential energy of SO2 is lost. This paper presents a novel UV photolytic process for prodn. of hydrogen from aq. Na2SO3 solns. The results show that the quantum efficiency of hydrogen prodn. can reach 14.4% under illumination from a low pressure mercury lamp. The mechanism occurs via two competing reaction pathways that involve oxidn. of SO32- to SO42- directly and through the dithionate (S2O62-) ion intermediate. The first route becomes dominant once a photostationary state for S2O62- is established. The initial pH of Na2SO3 soln. plays an important role in detg. both the hydrogen prodn. rate and the final products of the photolytic oxidn. At initial soln. pH of 9.80 Na2SO3 photooxidn. generates Na2SO4 as the final reaction product, while Na2S2O6 is merely a reaction intermediate. The highest hydrogen prodn. rate occurs when the initial soln. pH is 7.55. Redn. in the initial soln. pH to 5.93 results in disproportionation of HSO3- to elemental sulfur and SO42- but no hydrogen prodn.
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    Li, X.; Ma, J.; Liu, G.; Fang, J.; Yue, S.; Guan, Y.; Chen, L.; Liu, X. Efficient reductive dechlorination of monochloroacetic acid by sulfite/UV process. Environ. Sci. Technol. 2012, 46, 7342– 7349,  DOI: 10.1021/es3008535
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    Efficient Reductive Dechlorination of Monochloroacetic Acid by Sulfite/UV Process
    Li, Xuchun; Ma, Jun; Liu, Guifang; Fang, Jingyun; Yue, Siyang; Guan, Yinghong; Chen, Liwei; Liu, Xiaowei
    Environmental Science & Technology (2012), 46 (13), 7342-7349CODEN: ESTHAG; ISSN:0013-936X. (American Chemical Society)
    Most halogenated org. compds. (HOCs) are toxic and persistent, and their efficient destruction is currently a challenge. We propose a sulfite/UV (253.7 nm) process to eliminate HOCs. Monochloroacetic acid (MCAA) was selected as the target compd. and was degraded rapidly in the sulfite/UV process. The degrdn. kinetics were accelerated proportionally to the increased sulfite concn., while the significant enhancement by increasing pH only occurred at pH 6.0-8.7. The degrdn. proceeded via a reductive dechlorination mechanism induced by hydrated electron (eaq-), and complete dechlorination was readily achieved with almost all the Cl atoms in MCAA released as chlorides. Mass balance (C and Cl) studies showed that acetate, succinate, sulfoacetate, and chloride were the major products. A degrdn. pathway is proposed. The dual roles of pH were not only to regulate the S(IV) species distribution but also to control the interconversion between eaq- and H·. Effective quantum efficiency (Φ) for the formation of eaq- in the process was detd. to be 0.116±0.002 mol/einstein. This study may provide a promising alternative for complete dehalogenation of most HOCs and reductive detoxification of numerous toxicants.
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    Bentel, M. J.; Liu, Z.; Yu, Y.; Gao, J.; Men, Y.; Liu, J. Enhanced degradation of perfluorocarboxylic acids (PFCAs) by UV/sulfite treatment: Reaction mechanisms and system efficiencies at pH 12. Environ. Sci. Technol. Lett. 2020, 7, 351– 357,  DOI: 10.1021/acs.estlett.0c00236
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    Enhanced Degradation of Perfluorocarboxylic Acids (PFCA) by UV/Sulfite Treatment: Reaction Mechanisms and System Efficiencies at pH 12
    Bentel, Michael J.; Liu, Zekun; Yu, Yaochun; Gao, Jinyu; Men, Yujie; Liu, Jinyong
    Environmental Science & Technology Letters (2020), 7 (5), 351-357CODEN: ESTLCU; ISSN:2328-8930. (American Chemical Society)
    Reductive defluorination with UV-generated, hydrated electrons (eaq-) is a promising technol. to destroy perfluorocarboxylic acids (PFCA, CnF2n+1COO-); however, previous studies at pH 9-10 displayed a slow reaction rate, limited defluorination percentage (deF%), and high energy consumption. A substantially enhanced rate and extent of PFCA defluorination by operating a UV/sulfite system at optimized pH 12 are reported. Degrdn. kinetics and transformation products showed that at pH 12, eaq- cleaved multiple strong C-F bonds where were not cleaved at pH 9.5. The high pH condition also significantly favored the preferred decarboxylation pathway for deep defluorination. Compared to reactions at pH 9.5, an increase in soln. pH to 12 improved UV lamp energy efficiency 5 to 22-fold, enhanced C3-9 PFCA deF% to 73-93%, and reduced overall chem. consumption.
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  38. 38
    Liu, Z.; Bentel, M. J.; Yu, Y.; Ren, C.; Gao, J.; Pulikkal, V. F.; Sun, M.; Men, Y.; Liu, J. Near-quantitative defluorination of perfluorinated and fluorotelomer carboxylates and sulfonates with integrated oxidation and reduction. Environ. Sci. Technol. 2021, 55, 7052– 7062,  DOI: 10.1021/acs.est.1c00353
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    Near-quantitative defluorination of perfluorinated and fluorotelomer carboxylates and sulfonates with integrated oxidation and reduction
    Liu, Zekun; Bentel, Michael J.; Yu, Yaochun; Ren, Changxu; Gao, Jinyu; Pulikkal, Vivek Francis; Sun, Mei; Men, Yujie; Liu, Jinyong
    Environmental Science & Technology (2021), 55 (10), 7052-7062CODEN: ESTHAG; ISSN:0013-936X. (American Chemical Society)
    The UV-sulfite reductive treatment using hydrated electrons (eaq-) is a promising technol. for destroying perfluorocarboxylates (PFCAs, CnF2n+1COO-) in any chain length. However, the C-H bonds formed in the transformation products strengthen the residual C-F bonds and thus prevent complete defluorination. Reductive treatments of fluorotelomer carboxylates (FTCAs, CnF2n+1-CH2CH2-COO-) and sulfonates (FTSAs, CnF2n+1-CH2CH2-SO3-) are also sluggish because the ethylene linker separates the fluoroalkyl chain from the end functional group. In this work, we used oxidn. (Ox) with hydroxyl radicals (HO•) to convert FTCAs and FTSAs to a mixt. of PFCAs. This process also cleaved 35-95% of C-F bonds depending on the fluoroalkyl chain length. We probed the stoichiometry and mechanism for the oxidative defluorination of fluorotelomers. The subsequent redn. (Red) with UV-sulfite achieved deep defluorination of the PFCA mixt. for up to 90%. The following use of HO• to oxidize the H-rich residues led to the cleavage of the remaining C-F bonds. We examd. the efficacy of integrated oxidative and reductive treatment of n = 1-8 PFCAs, n = 4,6,8 perfluorosulfonates (PFSAs, CnF2n+1-SO3-), n = 1-8 FTCAs, and n = 4,6,8 FTSAs. A majority of structures yielded near-quant. overall defluorination (97-103%), except for n = 7,8 fluorotelomers (85-89%), n = 4 PFSA (94%), and n = 4 FTSA (93%). The results show the feasibility of complete defluorination of legacy PFAS pollutants and will advance both remediation technol. design and water sample anal.
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    Park, H.; Vecitis, C. D.; Cheng, J.; Dalleska, N. F.; Mader, B. T.; Hoffmann, M. R. Reductive degradation of perfluoroalkyl compounds with aquated electrons generated from iodide photolysis at 254 nm. Photochem. Photobiol. Sci. 2011, 10, 1945– 1953,  DOI: 10.1039/c1pp05270e
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    Reductive degradation of perfluoroalkyl compounds with aquated electrons generated from iodide photolysis at 254 nm
    Park, Hyunwoong; Vecitis, Chad D.; Cheng, Jie; Dalleska, Nathan F.; Mader, Brian T.; Hoffmann, Michael R.
    Photochemical & Photobiological Sciences (2011), 10 (12), 1945-1953CODEN: PPSHCB; ISSN:1474-905X. (Royal Society of Chemistry)
    The perfluoroalkyl compds. (PFCs), perfluoroalkyl sulfonates (PFXS) and perfluoroalkyl carboxylates (PFXA) are environmentally persistent and recalcitrant towards most conventional water treatment technologies. Here, we complete an in depth examn. of the UV-254 nm prodn. of aquated electrons during iodide photolysis for the reductive defluorination of six aquated perfluoroalkyl compds. (PFCs) of various headgroup and perfluorocarbon tail length. Cyclic voltammograms (CV) show that a potential of +2.0 V (vs. NHE) is required to induce PFC oxidn. and -1.0 V is required to induce PFC redn. indicating that PFC redn. is the thermodynamically preferred process. However, PFCs are obsd. to degrade faster during UV(254 nm)/persulfate (S2O82-) photolysis yielding sulfate radicals (E° = +2.4 V) as compared to UV(254 nm)/iodide (I-) photolysis yielding aquated electrons (E° = -2.9 V). Aquated electron scavenging by photoproduced triiodide (I3-), which achieved a steady-state concn. proportional to [PFOS]0, reduces the efficacy of the UV/iodide system towards PFC degrdn. PFC photoredn. kinetics are obsd. to be dependent on PFC headgroup, perfluorocarbon chain length, initial PFC concn., and iodide concn. From 2 to 12, pH had no observable effect on PFC photoredn. kinetics, suggesting that the aquated electron was the predominant reductant with negligible contribution from the H-atom. A large no. of gaseous fluorocarbon intermediates were semi-quant. identified and detd. to account for ∼25% of the initial PFOS carbon and fluorine. Reaction mechanisms that are consistent with kinetic observations are discussed.
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    Sauer, M. C.; Crowell, R. A.; Shkrob, I. A. Electron photodetachment from aqueous anions. 1. Quantum yields for generation of hydrated electron by 193 and 248 nm laser photoexcitation of miscellaneous inorganic anions. J. Phys. Chem. A 2004, 108, 5490– 5502,  DOI: 10.1021/jp049722t
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    Electron Photodetachment from Aqueous Anions. 1. Quantum Yields for Generation of Hydrated Electron by 193 and 248 nm Laser Photoexcitation of Miscellaneous Inorganic Anions
    Sauer, Myran C., Jr.; Crowell, Robert A.; Shkrob, Ilya A.
    Journal of Physical Chemistry A (2004), 108 (25), 5490-5502CODEN: JPCAFH; ISSN:1089-5639. (American Chemical Society)
    Time-resolved transient absorption spectroscopy has been used to det. quantum yields for electron photodetachment in 193 nm and (where possible) 248 nm laser excitation of misc. aq. anions, including hexacyanoferrate(II), sulfate, halide anions (Cl-, Br-, and I-), pseudohalide anions (OH-, HS-, and CNS-), and several common inorg. anions for which no quantum yields have been reported heretofore: SO32-, NO2-, NO3-, ClO3-, and ClO4-. Molar extinction coeffs. for these anions and photoproducts of electron detachment from these anions at the excitation wavelengths were also detd. These results are discussed in the context of recent ultrafast kinetic studies and compared with the previous data obtained by product analyses. The authors suggest using electron photodetachment from the aq. halide and pseudohalide anions as actinometric stds. for time-resolved studies of aq. photosystems in the UV.
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    Iwata, A.; Nakashima, N.; Kusaba, M.; Izawa, Y.; Yamanaka, C. Quantum yields of hydrated electrons by UV laser irradiation. Chem. Phys. Lett. 1993, 207, 137– 142,  DOI: 10.1016/0009-2614(93)87004-m
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    Quantum yields of hydrated electrons by UV laser irradiation
    Iwata, Akyhiro; Nakashima, Nobuaki; Kusaba, Mitsuhiro; Izawa, Yasukazu; Yamanaka, Chiyoe
    Chemical Physics Letters (1993), 207 (2-3), 137-42CODEN: CHPLBC; ISSN:0009-2614.
    Quantum yields of hydrated electrons of Cl-, Br-, I-, SO2-4, SCN-, and OH- in aq. soln. were detd. by 193 nm laser flash photolysis. Shorter wavelength excitation showed higher quantum yields for I- and SCN- ions in 3 wavelengths of 193, 222, and 248 nm. The highest yield was 0.73 for SO2-4 at 193 nm, and the lowest one was 0.015 for SCN- at 248 nm.
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    Qu, Y.; Zhang, C.; Li, F.; Chen, J.; Zhou, Q. Photo-reductive defluorination of perfluorooctanoic acid in water. Water Res. 2010, 44, 2939– 2947,  DOI: 10.1016/j.watres.2010.02.019
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    Photo-reductive defluorination of perfluorooctanoic acid in water
    Qu, Yan; Zhang, Chaojie; Li, Fei; Chen, Jing; Zhou, Qi
    Water Research (2010), 44 (9), 2939-2947CODEN: WATRAG; ISSN:0043-1354. (Elsevier B.V.)
    Globally distributed and highly stable, perfluorooctanoic acid (PFOA) has prompted much concern regarding its accumulation in the natural environment and its threats to ecosystems. Therefore, it is desirable to develop an effective treatment against PFOA pollution. In this study, a photo-redn. method is developed and evaluated for the decompn. of perfluorooctanoic acid (PFOA) in aq. phase with potassium iodide (KI) as a mediator. The expt. was conducted under 254 nm irradn. at room temp. and pH 9 under anaerobic conditions. UV photolysis of iodide solns. led to the generation of hydrated electrons (eaq -, Eaq/e°= -2.9 V), which contributed to the defluorination of PFOA. Defluorination was confirmed by fluoride release of 98%, indicating almost complete defluorination of PFOA. Kinetic anal. indicated that the PFOA decompn. fit the first-order model with a rate const. of 7.3 × 10-3 min-1. Besides fluoride ions, addnl. intermediates identified and quantified include formic acid, acetic acid, and six short-chain perfluorocarboxylic acids (C1-C6). Furthermore, small amts. of CF3H and C2F6 were also detected as reaction products by using GC/MS. With observation of the degrdn. products and verification via an isotopic labeling method, two major defluorination pathways of PFOA are proposed: direct cleavage of C-F bonds attacked by hydrated electrons as the nucleophile; and stepwise removal of CF2 by UV irradn. and hydrolysis. This method was applied to the decompn. of PFOA in wastewater issued from a fluorochem. plant and proved to be effective.
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    Wong, G. T. F.; Zhang, L.-S. Chemical removal of oxygen with sulfite for the polarographic or voltammetric determination of iodate or iodide in seawater. Mar. Chem. 1992, 38, 109– 116,  DOI: 10.1016/0304-4203(92)90070-q
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    Chemical removal of oxygen with sulfite for the polarographic or voltammetric determination of iodate or iodide in seawater
    Wong, George T. F.; Zhang, Ling Su
    Marine Chemistry (1992), 38 (1-2), 109-16CODEN: MRCHBD; ISSN:0304-4203.
    In the direct detn. of iodate and I- in seawater by differential pulse polarog. and cathodic stripping square wave voltammetry, resp., sulfite can be used to facilitate the removal of O in the samples before they are analyzed. The reaction between sulfite and dissolved O is almost instantaneous. In comparison with the removal of O by bubbling the sample with an inert gas alone, the time needed for the anal. of a sample for iodate and I- may be reduced to ∼15 min and 5 min, resp.
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    Yu, K.; Li, X.; Chen, L.; Fang, J.; Chen, H.; Li, Q.; Chi, N.; Ma, J. Mechanism and efficiency of contaminant reduction by hydrated electron in the sulfite/iodide/UV process. Water Res. 2018, 129, 357– 364,  DOI: 10.1016/j.watres.2017.11.030
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    Mechanism and efficiency of contaminant reduction by hydrated electron in the sulfite/iodide/UV process
    Yu, Keer; Li, Xuchun; Chen, Liwei; Fang, Jingyun; Chen, Huali; Li, Qiangbiao; Chi, Nianping; Ma, Jun
    Water Research (2018), 129 (), 357-364CODEN: WATRAG; ISSN:0043-1354. (Elsevier Ltd.)
    Advanced redn. by the extremely strong reducing species, hydrated electron (e-aq), is a promising and viable approach to eliminate a wide variety of persistent and toxic contaminants. In this study, we proposed a sulfite/iodide/UV process, which offered efficient prodn. of e-aq for contaminant redn. Using monochloroacetic acid (MCAA) as a simple e-aq probe, the availability of e-aq was assessed, and the mechanism involving the roles of S(IV) and iodide in the process was elucidated. A pronounced synergistic effect of S(IV) and iodide was obsd. in MCAA reductive dechlorination. The efficiency was much more dependent on the iodide concn. due to its higher absorptivity and quantum yield of e-aq. S(IV) played a dual role by producing e-aq via photoionization of SO2-3 and by reducing the reactive iodine species formed to avoid their scavenging of e-aq. When S(IV) was available, cycling of iodide occurred, favoring the const. e-aq prodn. The formation and transformation kinetics of sulfite radical were studied to verify the roles of S(IV) and iodide in the process. A kinetic model of MCAA dechlorination was also developed to quantify the e-aq-initiated redn. efficiency, highlighting the effects of S(IV), iodide, and pH. High pH favored the redn., and the process was still effective in field surface water. This study underscores the importance of producing e-aq efficiently and of minimizing the e-aq scavenging of intermediates inherently formed and accumulated, and highlights the potential of the sulfite/iodide/UV process to efficiently eliminate recalcitrant contaminants.
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    Environmental Science & Technology (2020), 54 (11), 6957-6967CODEN: ESTHAG; ISSN:0013-936X. (American Chemical Society)
    UV photochem. reactions of a sulfite (SO32-) photo-sensitizer generates strongly reducing hydrated electrons (eaq-; NHE = -2.9 V) shown to effectively degrade individual per- and polyfluoroalkyl substances (PFAS), including perfluorooctanesulfonic acid (PFOS) and perfluorooctanoic acid (PFOA). However, treatment of complex PFAS mixts. in aq. film-forming foam (AFFF) is largely unknown. UV-sulfite was applied to a dild. AFFF to characterize eaq- reactions with 15 PFAS identified by liq. chromatog./quadrupole time-of-flight mass spectrometry targeted anal. Results showed reactivity varied widely among PFAS, but reaction rates obsd. for individual PFAS in AFFF were similar to rates obsd. in single-solute expts. While some structures, including long-chain perfluoroalkyl sulfonic acids (PFSA) and perfluoroalkyl carboxylic acids (PFCA), were readily degraded, other structures, most notably short-chain PFSA and fluorotelomer sulfonic acids (FTS), were more recalcitrant. These results were consistent with those showing incomplete F- release (up to 53% of F content in AFFF) during reactions. Results also showed selected PFSA, PFCA, and FTS can form as transient intermediates or un-reactive end-products via eaq- reactions with precursor structures in AFFF. This indicated that while UV-sulfite treatment can effectively treat PFOS and PFOA to meet health advisory levels, remediation of the wider range of PFAS in AFFF is more challenging.
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    Advanced oxidn. processes (AOPs), which involve the in-situ generation of highly potent chem. oxidants such as the hydroxyl radical (·OH), have recently emerged as an important class of technologies for accelerating the oxidn. and hence destruction of a wide range of org. contaminants in polluted water and air. We propose generally applicable std. figures-of-merit for comparing these waste treatment technologies. These figures-of-merit are based on elec. energy consumption within two phenomenol. kinetic order regimes: one for high contaminant concns. (elec. energy per mass, EE/M) and one for low concns. (elec. energy per order of magnitude per m3, EE/O). We also point out that a simple understanding of the overall kinetic behavior of org. destruction in a waste stream (i.e. whether zero or first order) is necessary for describing meaningful elec. efficiencies. These std. figures-of-merit provide a direct link to the elec. efficiency (lower values mean higher efficiency) of an advanced oxidn. process, independent of the nature of the system and therefore allow for direct comparison of widely disparate AOP technologies. We have also shown that the EE/M and EE/O parameters are inversely proportional to fundamental efficiency factors, such as the lamp efficiency, the fraction of the emitted light flux that is absorbed in the water and the quantum yield of generation of active radicals.
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    Environmental Science & Technology (2021), 55 (20), 14146-14155CODEN: ESTHAG; ISSN:1520-5851. (American Chemical Society)
    Omega-hydroperfluorocarboxylates (ω-HPFCAs, HCF2-(CF2)n-1-COO-) are com. available in bulk quantities and have been applied in agrochems., fluoropolymer prodn., and semiconductor coating. In this study, we used kinetic measurements, theor. calcns., model compd. expts., and transformation product analyses to reveal novel mechanistic insights into the reductive and oxidative transformation of ω-HPFCAs. Like perfluorocarboxylates (PFCAs, CF3-(CF2)n-1-COO-), the direct linkage between HCnF2n- and -COO- enables facile degrdn. under UV/sulfite treatment. To our surprise, the presence of the H atom on the remote carbon makes ω-HPFCAs more susceptible than PFCAs to decarboxylation (i.e., yielding shorter-chain ω-HPFCAs) and less susceptible to hydrodefluorination (i.e., H/F exchange). Like fluorotelomer carboxylates (FTCAs, CnF2n+1-CH2CH2-COO-), the C-H bond in HCF2-(CF2)n-1-COO- allows hydroxyl radical oxidn. and limited defluorination. While FTCAs yielded PFCAs in all chain lengths, ω-HPFCAs only yielded -OOC-(CF2)n-1-COO- (major) and -OOC-(CF2)n-2-COO- (minor) due to the unfavorable β-fragmentation pathway that shortens the fluoroalkyl chain. We also compared two treatment sequences-UV/sulfite followed by heat/persulfate and the reverse-toward complete defluorination of ω-HPFCAs. The findings will benefit the treatment and monitoring of H-contg. per- and polyfluoroalkyl substance (PFAS) pollutants as well as the design of future fluorochems.
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    Gregor, Harry P.; Belle, Jack; Marcus, R. A.
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    Hildebrand, J. H.; Benesi, H. A.; Mower, L. M.
    Journal of the American Chemical Society (1950), 72 (), 1017-20CODEN: JACSAT; ISSN:0002-7863.
    The soly. of I in CS2, 2,2-dimethylbutane, cyclohexane, EtOH, Et2O, p-xylene, mesitylene, and C7F16 at 0.0° is 2.440, 0.164, -, 3.51, 6.54, -, 6.89, and 0.0038 mole %, resp.; at 25.0°, 5.58, 0.469, 0.918, 4.71, 8.96, 7.66, 10.72, and 0.0182 mole %, resp.; and at 35°, 7.64, 0.684, 1.329, 5.59, 10.43. 9.54, - and 0.0286 mole %, resp. The solvation in the case of mesitylene and p-xylene increases the I soly. over the value for regular solns., the increase being greatest for mesitylene. The enhancement of I solubilities in these solvents is in good agreement with equil. data obtained from earlier spectroscopic measurements (C.A. 43, 7824h) and therefore provides further evidence for the existence of an acid-base interaction between aromatic hydrocarbons and I. The I solubilities in unsolvated solns. are in accord with the behavior predicted from the internal pressures of the pure solvents.
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  • Abstract

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    Figure 1

    Figure 1. (a) Parent compound decay and (b) defluorination of PFBS by UV/S (10 mM), UV/I (2 mM), and UV/S (10 mM) + I (2 mM); PFBS degradation by UV/S + I at varied (c,d) iodide concentrations, (e) sulfite concentrations, and (f) solution pH. Default reaction conditions: PFBS (0.025 mM), carbonate (5 mM), pH 12.0, 254 nm irradiation (an 18 W low-pressure Hg lamp in 600 mL solution), and 20 °C.

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    Figure 2

    Figure 2. (a) Parent compound decay and (b) defluorination of n = 1–7 PFCAs by UV/S (10 mM), and UV/S (10 mM) + I (2 mM). Panel (c) shows the magnified defluorination profiles for n = 2–7 PFCAs (averaged) within the first 1 h. (d–f) Parent compound decay and defluorination of n = 4, 6, 8 PFSAs. Reaction conditions: individual PFAS (0.025 mM), NaHCO3 (5 mM), pH 12.0, 254 nm irradiation (an 18 W low-pressure Hg lamp in 600 mL solution), and 20 °C.

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    Figure 3

    Figure 3. Parent compound decay, TP formation, and defluorination of tri-, di-, and monofluoro acetates by (a–c) UV/S + I and (d–f) UV/S and (g) reaction schemes. Reaction conditions: individual PFAS (0.025 mM), Na2SO3 (10 mM), KI (2 mM), NaHCO3 (5 mM), pH 12.0, 254 nm irradiation (an 18 W low-pressure Hg lamp in 600 mL solution), and 20 °C. The vertical red dotted lines in panels (d–f) indicate the 1 h time window where 100% defluorination by UV/S + I was achieved.

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    Figure 4

    Figure 4. Parent compound decay, TP formation, and defluorination of PFPrA by (a,b) UV/S + I and (c,d) UV/S. Panels (b,d) show magnified time profiles within the first hour of reaction. Panel (e) shows the proposed reaction schemes. Reaction conditions: PFPrA (0.025 mM), Na2SO3 (10 mM), KI (2 mM), NaHCO3 (5 mM), pH 12.0, 254 nm irradiation (an 18 W low-pressure Hg lamp in 600 mL solution), and 20 °C.

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    Figure 5

    Figure 5. Parent compound decay and TP formation for the degradation of (a,b) PFOA and (c,d) PFBS by UV/S + I and UV/S. Panel (e) shows the proposed reaction schemes. Reaction conditions were the following: individual PFAS (0.025 mM), Na2SO3 (10 mM), KI (2 mM), NaHCO3 (5 mM), pH 12.0, 254 nm irradiation (an 18 W low-pressure Hg lamp in 600 mL solution), and 20 °C.

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    Figure 6

    Figure 6. (a) Kinetic profiles of transient absorption at 700 nm after the 266 nm laser pulse excitation of I, S, and S + I solutions; (b) kinetic profiles of transient absorption at 350 nm after 266 nm laser pulse excitation of I and S + I solutions; (c) decay of sulfite in UV/S and UV/S + I in the absence of PFAS; and (d) lifetime of eaq– in UV/S + I at varied solution pH. Conditions: Na2SO3 (S, 10 mM), KI (I, 2 mM), and pH 12.0.

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    Figure 7

    Figure 7. (a) DeF% of PFCAs by UV/S after 8 h; (b) time profiles for the defluorination from 0.25 mM PFOA by UV/S (with SO32– spikes every 24 h) and UV/S + I (no SO32– spike); (c) time profiles for the defluorination from various [PFOA]0 by UV/S + I; (d) deF% of PFCAs after 24 h by UV/S + I; (e) deF% of PFSAs by UV/I and UV/S + I after 24 h; (f) time profiles for the defluorination from the mixed PFAS (see Table 2) in NaCl brine after a 1:1 dilution with deionized (DI) water. Default reaction conditions: 10 mM Na2SO3 (10 mM), KI (2 mM for UV/S + I), NaHCO3 (5 mM), pH 12.0, and 254 nm irradiation (an 18 W low-pressure Hg lamp for 600 mL solution), and 20 °C.

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    This article references 58 other publications.

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      Ng, C.; Cousins, I. T.; DeWitt, J. C.; Glüge, J.; Goldenman, G.; Herzke, D.; Lohmann, R.; Miller, M.; Patton, S.; Scheringer, M.; Trier, X.; Wang, Z. Addressing urgent questions for PFAS in the 21st Century. Environ. Sci. Technol. 2021, 55, 12755– 12765,  DOI: 10.1021/acs.est.1c03386
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      Addressing Urgent Questions for PFAS in the 21st Century
      Ng, Carla; Cousins, Ian T.; DeWitt, Jamie C.; Gluge, Juliane; Goldenman, Gretta; Herzke, Dorte; Lohmann, Rainer; Miller, Mark; Patton, Sharyle; Scheringer, Martin; Trier, Xenia; Wang, Zhanyun
      Environmental Science & Technology (2021), 55 (19), 12755-12765CODEN: ESTHAG; ISSN:1520-5851. (American Chemical Society)
      A review. Despite decades of research on per- and polyfluoroalkyl substances (PFAS), fundamental obstacles remain to addressing worldwide contamination by these chems. and their assocd. impacts on environmental quality and health. Here, we propose six urgent questions relevant to science, technol., and policy that must be tackled to address the "PFAS problem": (1) What are the global prodn. vols. of PFAS, and where are PFAS used (2) Where are the unknown PFAS hotspots in the environment (3) How can we make measuring PFAS globally accessible (4) How can we safely manage PFAS-contg. waste (5) How do we understand and describe the health effects of PFAS exposure (6) Who pays the costs of PFAS contamination. The importance of each question and barriers to progress are briefly described, and several potential paths forward are proposed. Given the diversity of PFAS and their uses, the extreme persistence of most PFAS, the striking ongoing lack of fundamental information, and the inequity of the health and environmental impacts from PFAS contamination, there is a need for scientific and regulatory communities to work together, with cooperation from PFAS-related industries, to fill in crit. data gaps and protect human health and the environment.
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      Rericha, Y.; Cao, D.; Truong, L.; Simonich, M.; Field, J. A.; Tanguay, R. L. Behavior effects of structurally diverse per- and polyfluoroalkyl substances in zebrafish. Chem. Res. Toxicol. 2021, 34, 1409– 1416,  DOI: 10.1021/acs.chemrestox.1c00101
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      Behavior Effects of Structurally Diverse Per- and Polyfluoroalkyl Substances in Zebrafish
      Rericha, Yvonne; Cao, Dunping; Truong, Lisa; Simonich, Michael; Field, Jennifer A.; Tanguay, Robyn L.
      Chemical Research in Toxicology (2021), 34 (6), 1409-1416CODEN: CRTOEC; ISSN:0893-228X. (American Chemical Society)
      Per- and polyfluoroalkyl substances (PFAS) are ubiquitously detected in the environment, and some pose significant human and environmental health concerns globally. While some PFAS induce adverse health effects, relatively few toxicol. studies adequately address the broad structural diversity of this chem. class. In the current study, we evaluated 58 individual PFAS spanning 14 structural subclasses and 2 mixts. at single concns. for developmental toxicity in zebrafish using highly sensitive behavior endpoints. Following developmental exposure to PFAS, zebrafish were assessed for mortality and challenged with an embryonic photomotor response (EPR) assay at 24 h postfertilization (hpf) and with larval photomotor response (LPR) and larval startle response assays at 120 hpf. We found that none of the tested PFAS exposures elicited significant mortality or aberrant EPR; however, exposure to 21 individual PFAS from multiple structural subclasses and 1 mixt. induced aberrant larval behavior. We then evaluated developmental toxicity across a concn. range of 0-100μM for 10 perfluoroalkyl carboxylic acids (PFCAs; 4-carbon perfluorobutanoic acid through the 13-carbon perfluorotridecanoic acid). Exposure to the PFCAs did not cause significant mortality or morphol. effects, with the exception of perfluorooctanoic acid and perfluorononanoic acid, and did not induce aberrant EPR. All PFCAs, except for longer-chain perfluorododecanoic acid caused abnormal LPR following exposure to at least one concn. In this study, we evaluated a broad set of PFAS not previously assessed for in vivo sublethal behavior endpoints and confirmed previous findings that exposure to some PFAS induces abnormal behavior in developing zebrafish. The data from this study will guide the selection of PFAS for which to investigate modes of toxic action.
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      Dasgupta, S.; Reddam, A.; Liu, Z.; Liu, J.; Volz, D. C. High-content screening in zebrafish identifies perfluorooctanesulfonamide as a potent developmental toxicant. Environ. Pollut. 2020, 256, 113550,  DOI: 10.1016/j.envpol.2019.113550
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      High-content screening in zebrafish identifies perfluorooctanesulfonamide as a potent developmental toxicant
      Dasgupta, Subham; Reddam, Aalekhya; Liu, Zekun; Liu, Jinyong; Volz, David C.
      Environmental Pollution (Oxford, United Kingdom) (2020), 256 (), 113550CODEN: ENPOEK; ISSN:0269-7491. (Elsevier Ltd.)
      Per- and polyfluoroalkyl substances (PFASs) have been used for decades within industrial processes and consumer products, resulting in frequent detection within the environment. Using zebrafish embryos, we screened 38 PFASs for developmental toxicity and revealed that perfluorooctanesulfonamide (PFOSA) was the most potent developmental toxicant, resulting in elevated mortality and developmental abnormalities following exposure from 6 to 24 h post fertilization (hpf) and 6 to 72 hpf. PFOSA resulted in a concn.-dependent increase in mortality and abnormalities, with surviving embryos exhibiting a >12-h delay in development at 24 hpf. Exposures initiated at 0.75 hpf also resulted in a concn.-dependent delay in epiboly, although these effects were not driven by a specific sensitive window of development. We relied on mRNA-sequencing to identify the potential assocn. of PFOSA-induced developmental delays with impacts on the embryonic transcriptome. Relative to stage-matched vehicle controls, these data revealed that pathways related to hepatotoxicity and lipid transport were disrupted in embryos exposed to PFOSA from 0.75 to 14 hpf and 0.75 to 24 hpf. Therefore, we measured liver area as well as neutral lipids in 128-hpf embryos exposed to vehicle (0.1% DMSO). Overall, our findings show that early exposure to PFOSA adversely impacts embryogenesis, an effect that may lead to altered lipid transport and liver development.
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      Nguyen, G. T. H.; Nocentini, A.; Angeli, A.; Gratteri, P.; Supuran, C. T.; Donald, W. A. Perfluoroalkyl substances of significant environmental concern can strongly inhibit human carbonic anhydrase isozymes. Anal. Chem. 2020, 92, 4614– 4622,  DOI: 10.1021/acs.analchem.0c00163
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      Perfluoroalkyl Substances of Significant Environmental Concern Can Strongly Inhibit Human Carbonic Anhydrase Isozymes
      Nguyen, Giang T. H.; Nocentini, Alessio; Angeli, Andrea; Gratteri, Paola; Supuran, Claudiu T.; Donald, William A.
      Analytical Chemistry (Washington, DC, United States) (2020), 92 (6), 4614-4622CODEN: ANCHAM; ISSN:0003-2700. (American Chemical Society)
      Perfluoroalkyl substances (PFASs) persist and are ubiquitous in the environment. The origins of PFAS toxicity and how they specifically affect the functions of proteins remain unclear. Herein, we report that PFASs can strongly inhibit the activity of human carbonic anhydrases (hCAs), which are ubiquitous enzymes that catalyze the hydration of CO2, are abundant in the blood and organs of mammals, and involved in pH regulation, ion homeostasis, and biosynthesis. The interactions between PFASs and hCAs were investigated using stopped-flow kinetic enzyme-inhibition measurements, native mass spectrometry (MS), and ligand-docking simulations. Narrow-bore emitters in native MS with inner diams. of ∼300 nm were used to directly and simultaneously measure the dissocn. consts. of 11 PFASs to an enzyme, which was not possible using conventional emitters. The data from native MS and stopped-flow measurements were in excellent agreement. Of 15 PFASs investigated, eight can inhibit at least one of four hCA isoenzymes (I, II, IX, and XII) with submicromolar inhibition consts., including perfluorooctanoic acid, perfluorooctanesulfonamide, and perfluorooctanesulfonic acid. Some PFASs, including those with both short and long perfluoromethylene chains, can effectively inhibit at least one hCA isoenzyme with low nanomolar inhibition consts.
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    5. 5
      Harris, M. H.; Rifas-Shiman, S. L.; Calafat, A. M.; Ye, X.; Mora, A. M.; Webster, T. F.; Oken, E.; Sagiv, S. K. Predictors of per- and polyfluoroalkyl substance (PFAS) plasma concentrations in 6–10 year old American children. Environ. Sci. Technol. 2017, 51, 5193– 5204,  DOI: 10.1021/acs.est.6b05811
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      Predictors of Per- and Polyfluoroalkyl Substance (PFAS) Plasma Concentrations in 6-10 Year Old American Children
      Harris, Maria H.; Rifas-Shiman, Sheryl L.; Calafat, Antonia M.; Ye, Xiaoyun; Mora, Ana Maria; Webster, Thomas F.; Oken, Emily; Sagiv, Sharon K.
      Environmental Science & Technology (2017), 51 (9), 5193-5204CODEN: ESTHAG; ISSN:0013-936X. (American Chemical Society)
      Certain per- and polyfluoroalkyl substances (PFASs) are suspected developmental toxicants, but data on PFAS concns. and exposure routes in children are limited. The authors measured plasma PFASs in children aged 6-10 years from the Boston-area Project Viva pre-birth cohort, and used multivariable linear regression to est. assocns. with sociodemog., behavioral, and health-related factors, and maternal PFASs measured during pregnancy. PFAS concns. in Project Viva children (sampled 2007-2010) were similar to concns. among youth participants (aged 12-19 years) in the 2007-8 and 2009-10 National Health and Nutrition Examn. Survey (NHANES); mean concns. of most PFASs declined from 2007 to 2010 in Project Viva and NHANES. In mutually-adjusted models, predictors of higher PFAS concns. included older child age, lower adiposity, carpeting or a rug in the child's bedroom, higher maternal education, and higher neighborhood income. Concns. of perfluorooctane sulfonate (PFOS), perfluorooctanoate (PFOA), perfluorohexane sulfonate (PFHxS), and 2-(N-methyl-perfluorooctane sulfonamido) acetate (Me-PFOSA-AcOH) were 26-36% lower in children of black mothers compared to children of white mothers and increased 12-21% per interquartile range increase in maternal pregnancy PFASs. Breastfeeding duration did not predict childhood PFAS concns. in adjusted multivariable models. Together, the studied predictors explained the obsd. variability in PFAS concns. to only a modest degree.
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      Nian, M.; Luo, K.; Luo, F.; Aimuzi, R.; Huo, X.; Chen, Q.; Tian, Y.; Zhang, J. Association between prenatal exposure to PFAS and fetal sex hormones: Are the short-chain PFAS safer?. Environ. Sci. Technol. 2020, 54, 8291– 8299,  DOI: 10.1021/acs.est.0c02444
      6
      Association between Prenatal Exposure to PFAS and Fetal Sex Hormones: Are the Short-Chain PFAS Safer?
      Nian, Min; Luo, Kai; Luo, Fei; Aimuzi, Ruxianguli; Huo, Xiaona; Chen, Qian; Tian, Ying; Zhang, Jun
      Environmental Science & Technology (2020), 54 (13), 8291-8299CODEN: ESTHAG; ISSN:0013-936X. (American Chemical Society)
      Epidemiol. evidence regarding the effects of in utero exposure to per- and polyfluoroalkyl substances (PFAS), particularly short-chain PFAS, on fetal reproductive hormones is limited and inconsistent. This study aimed to assess the relationship between maternal PFAS exposure and fetal reproductive hormones. A total of 752 mother-infant pairs who were recruited in the Shanghai Birth Cohort Study between 2013 and 2016 were selected. We quantified 10 PFAS, including two short-chain PFAS congeners (perfluorobutanesulfonate, PFBS and perfluoroheptanoic acid, PFHpA), in maternal blood plasma in early pregnancy. Dehydroepiandrosterone sulfate (DHEA-S), sex hormone-binding globulin (SHBG), LH, FSH and total testosterone (TT) were measured in the umbilical cord blood using chemiluminescence kits. Free androgen index (FAI) was calcd. by TT divided by SHBG. Multiple linear regression found that one ln-unit increase in maternal PFBS was assocd. with decreases in FSH (-0.159; 95% CI: -0.290, -0.029), LH (-0.113; 95% CI: -0.221, -0.004), and FAI (-0.009; 95% CI: -0.017, -0.001). In addn., PFHpA showed neg. assocns. with LH (-0.154; 95% CI: -0.297, -0.011) and FAI (-0.008; 95% CI: -0.014, -0.002). When PFAS were analyzed in quartiles, significant neg. assocns. were obsd. between PFBS and FSH, and between PFHpA and FAI. Overall, prenatal exposure to PFBS and PFHpA was assocd. with the disturbance of fetal gonadotropins as well as free androgen level in this prospective cohort, suggesting that the reproductive toxicity of short-chain PFAS may not be neglected.
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    7. 7
      Zheng, G.; Schreder, E.; Dempsey, J. C.; Uding, N.; Chu, V.; Andres, G.; Sathyanarayana, S.; Salamova, A. Per- and polyfluoroalkyl substances (PFAS) in breast milk: Concerning trends for current-use PFAS. Environ. Sci. Technol. 2021, 55, 7510– 7520,  DOI: 10.1021/acs.est.0c06978
      7
      Per- and polyfluoroalkyl substances (PFAS) in breast milk: Concerning trends for current-use kPFAS
      Zheng, Guomao; Schreder, Erika; Dempsey, Jennifer C.; Uding, Nancy; Chu, Valerie; Andres, Gabriel; Sathyanarayana, Sheela; Salamova, Amina
      Environmental Science & Technology (2021), 55 (11), 7510-7520CODEN: ESTHAG; ISSN:0013-936X. (American Chemical Society)
      This is the first study in the last 15 years to analyze per- and polyfluoroalkyl substances (PFAS) in breast milk collected from mothers (n = 50) in the United States, and our findings indicate that both legacy and current-use PFAS now contaminate breast milk, exposing nursing infants. Breast milk was analyzed for 39 PFAS, including 9 short-chain and 30 long-chain compds., and 16 of these PFAS were detected in 4-100% of the samples. The .sum.PFAS concn. in breast milk ranged from 52.0 to 1850 pg/mL with a median concn. of 121 pg/mL. Perfluorooctanesulfonic acid (PFOS) and perfluorooctanoic acid (PFOA) were the most abundant PFAS in these samples (medians 30.4 and 13.9 pg/mL, resp.). Two short-chain PFAS, including perfluoro-n-hexanoic acid (PFHxA, C6) and perfluoro-n-heptanoic acid (PFHpA, C7), were detected in most of the samples with median concns. of 9.69 and 6.10 pg/mL, resp. Anal. of the available breast milk PFAS data from around the world over the period of 1996-2019 showed that while the levels of the phased-out PFOS and PFOA have been declining with halving times of 8.1 and 17 years, resp., the detection frequencies of current-use short-chain PFAS have been increasing with a doubling time of 4.1 years.
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    8. 8
      Xiao, X.; Ulrich, B. A.; Chen, B.; Higgins, C. P. Sorption of poly- and perfluoroalkyl substances (PFASs) relevant to aqueous film-forming foam (AFFF)-impacted groundwater by biochars and activated carbon. Environ. Sci. Technol. 2017, 51, 6342– 6351,  DOI: 10.1021/acs.est.7b00970
      8
      Sorption of Poly- and Perfluoroalkyl Substances (PFASs) Relevant to Aqueous Film-Forming Foam (AFFF)-Impacted Groundwater by Biochars and Activated Carbon
      Xiao, Xin; Ulrich, Bridget A.; Chen, Baoliang; Higgins, Christopher P.
      Environmental Science & Technology (2017), 51 (11), 6342-6351CODEN: ESTHAG; ISSN:0013-936X. (American Chemical Society)
      Despite growing concerns about human exposure to perfluorooctanoate (PFOA) and perfluorooctanesulfonate (PFOS), other poly- and perfluoroalkyl substances (PFASs) derived from aq. film-forming foams (AFFFs) have garnered little attention. While these other PFASs may also be present in AFFF-impacted drinking water, their removal by conventional drinking-water treatment is poorly understood. This study compared the removal of 30 PFASs, including 13 recently discovered PFASs, from an AFFF-impacted drinking water using carbonaceous sorbents (i.e., granular activated carbon, GAC). The approach combined lab. batch expts. and modeling: batch sorption data were used to det. partition coeffs. (Kd) and calibrate a transport model based on intraparticle diffusion-limited sorption kinetics, which was used to make forward predictions of PFAS breakthrough during GAC adsorption. While strong retention was predicted for PFOS and PFOA, nearly all of the recently discovered polyfluorinated chems. and PFOS-like PFASs detected in the AFFF-impacted drinking water were predicted to break through GAC systems before both PFOS and PFOA. These model breakthrough results were used to evaluate a simplified approach to predicting PFAS removal by GAC using compd.-specific retention times on a C18 column (RTC18). Overall, this study reveals that GAC systems for the treatment of AFFF-impacted sources of water for PFOA and PFOS likely achieve poor removal, when operated only for the treatment of PFOS and PFOA, of many unmonitored PFASs of unknown toxicity.
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    9. 9
      McCleaf, P.; Englund, S.; Östlund, A.; Lindegren, K.; Wiberg, K.; Ahrens, L. Removal efficiency of multiple poly- and perfluoroalkyl substances (PFASs) in drinking water using granular activated carbon (GAC) and anion exchange (AE) column tests. Water Res. 2017, 120, 77– 87,  DOI: 10.1016/j.watres.2017.04.057
      9
      Removal efficiency of multiple poly- and perfluoroalkyl substances (PFASs) in drinking water using granular activated carbon (GAC) and anion exchange (AE) column tests
      McCleaf, Philip; Englund, Sophie; Oestlund, Anna; Lindegren, Klara; Wiberg, Karin; Ahrens, Lutz
      Water Research (2017), 120 (), 77-87CODEN: WATRAG; ISSN:0043-1354. (Elsevier Ltd.)
      Poly- and perfluoroalkyl substances (PFASs) have been detected in drinking water at relatively high concns. throughout the world which has led to implementation of regulatory guidelines for specific PFASs in drinking water in several European countries and in the U.S. The Swedish National Food Agency has detd. that the drinking water of over one third of the country's municipal consumers is at risk or already affected by PFAS contamination. The present study investigated the effects of perfluorocarbon chain length, functional group and isomer structure (branched or linear) on removal of multiple PFASs using granular activated carbon (GAC, Filtrasorb 400) and anion exchange (AE, Purolite A600) column expts. The removal of 14 different PFASs, i.e. the C3-C11, C14 perfluoroalkyl carboxylic acids (PFCAs) (PFBA, PFPeA, PFHxA, PFHpA, PFOA, PFNA, PFDA, PFUnDA, PFDoDA, PFTeDA), perfluorooctane sulfonamide (FOSA), and the C4, C6, C8 perfluoroalkyl sulfonic acids (PFSAs) (PFBS, PFHxS, PFOS), was monitored for a 217 day period. The results indicate the selective nature of PFAS removal as the absorbents are loaded with PFASs and dissolved org. carbon (DOC). A clear relationship between perfluorocarbon chain length and removal efficiency of PFASs using GAC and AE was found while PFASs with sulfonate functional groups displayed greater removal efficiency than those with carboxylate groups. Similarly, time to column breakthrough increased with increasing perfluorocarbon chain length and was greater for the PFSAs than the PFCAs for both GAC and AE. Shorter carbon chained PFASs such as PFBA, PFPeA, PFHxA showed desorption behavior and long-chained PFASs showed increased removal towards the end of the expt. indicating agglomeration or micelle development. Linear isomers of PFOS, PFHxS, and perfluorooctane sulfonamide (FOSA) had greater column removal efficiencies using GAC (and also for AE at greater bed vol. throughput) than the branched and this difference increased at greater bed vol. throughputs. The GAC and AE columns showed a poor correlation between DOC and PFAS removal efficiency. The results indicate that designers and operators of AE and GAC treatment processes must take into consideration the selective nature of PFAS removal and assocd. desorption of short-chain PFCAs during co-removal of multiple PFASs.
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    10. 10
      Fang, Y.; Ellis, A.; Choi, Y. J.; Boyer, T. H.; Higgins, C. P.; Schaefer, C. E.; Strathmann, T. J. Removal of per-and polyfluoroalkyl substances (PFASs) in aqueous film-forming foam (AFFF) using ion-exchange and nonionic resins. Environ. Sci. Technol. 2021, 55, 5001– 5011,  DOI: 10.1021/acs.est.1c00769
      10
      Removal of per- and polyfluoroalkyl substances (PFASs) in aqueous film-forming foam (AFFF) using ion-exchange and nonionic resins
      Fang, Yida; Ellis, Anderson; Choi, Youn Jeong; Boyer, Treavor H.; Higgins, Christopher P.; Schaefer, Charles E.; Strathmann, Timothy J.
      Environmental Science & Technology (2021), 55 (8), 5001-5011CODEN: ESTHAG; ISSN:0013-936X. (American Chemical Society)
      Despite benefits to the firefighting industry, the release of per- and polyfluoroalkyl substances (PFASs) from aq. film-forming foam (AFFF) into aquatic systems poses significant risks to human health and other organisms. While anion-exchange technologies have proven to be effective for removing perfluoroalkyl acids (PFAAs) from water, their effectiveness for removing the diverse PFAS structures discovered in AFFF remains unknown. Here, we report on the adsorption of 75 PFASs, including 63 polyfluorinated substances, in a dild. AFFF mixt. using 14 com. available ion-exchange (IX)/nonionic resins and granular activated carbon (GAC). Results showed that anion-exchange resins (AERs) exhibited significant adsorption of PFASs compared to cation-exchange resins (CERs), nonionic resins (NIRs), and GAC regardless of the PFAS's predicted charge. Isotherm data showed that macroporous AERs have a higher PFAS adsorption capacity compared to gel-type AERs. Cross-correlation comparison of PFAS/Cl- selectivity coeffs. (Kex) for each PFAS-AER combination showed that the hydrophobicity of the AER functional group, and polymer matrix played a dominant role in detg. resin affinity for PFASs. PFAS structural characteristics also significantly affected adsorption, with increasing chain length and a net neg. charge increasing the extent of adsorption. Results from this study provide guidelines for the selection of resins to adsorb a wider range of PFASs and meaningful insights for the development of quant. models for IX treatment of AFFF-impacted water.
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    11. 11
      Liu, Y.-L.; Sun, M. Ion exchange removal and resin regeneration to treat per- and polyfluoroalkyl ether acids and other emerging PFAS in drinking water. Water Res. 2021, 207, 117781,  DOI: 10.1016/j.watres.2021.117781
      11
      Ion exchange removal and resin regeneration to treat per- and polyfluoroalkyl ether acids and other emerging PFAS in drinking water
      Liu, Yen-Ling; Sun, Mei
      Water Research (2021), 207 (), 117781CODEN: WATRAG; ISSN:0043-1354. (Elsevier Ltd.)
      Ion exchange (IX) is a promising technol. to remove legacy anionic per- and polyfluoroalkyl substances (PFAS) from water. As increasing nos. of per- and polyfluoroalkyl ether acids (PFEA) and other emerging PFAS were detected in the environment, it is necessary to understand how well IX resins remove these emerging PFAS for drinking water treatment. In this study, nine com. available IX resins were tested to treat a drinking water source spiked with 40 legacy and emerging PFAS at 600 ng/L, including PFEA, perfluoroalkyl carboxylic and sulfonic acids, fluorotelomer sulfonic acids, perfluoroalkane sulfonamides, perfluoroalkane sulfonamidoacetic acids, and zwitterionic species. With limited contact time (15 min), PFAS properties such as the fluorinated chain length, charge, and functional groups all affected PFAS adsorption to resins. However, the impact of PFAS properties on PFAS removal became less pronounced when the contact time increased beyond 2 h, while the resin polymer matrix became the crit. factor for PFAS removal. All five tested polystyrene-divinylbenzene (PS-DVB) resins achieved more than 90% removal in 24 h of 35 PFAS compds., while polymethacrylate and polyacrylic resins achieved >90% removal for less than half of the compds. Regenerating PS-DVB resin was investigated using different salt species, regenerant pH, brine concns., and methanol contents. Sodium chloride and ammonium chloride were found the best brines for regenerating the tested resins. Increasing brine concns. enhanced the regeneration efficiency, esp. for short-chain PFAS. Using simple salt regenerants, up to 94% of selected short-chain PFAS was released from resins designed for general water treatment, but no meaningful regeneration was achieved for long-chain PFAS or PFAS-specific resins when the org. solvent content was less than 20%.
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    12. 12
      Steinle-Darling, E.; Reinhard, M. Nanofiltration for trace organic contaminant removal: Structure, solution, and membrane fouling effects on the rejection of perfluorochemicals. Environ. Sci. Technol. 2008, 42, 5292– 5297,  DOI: 10.1021/es703207s
      12
      Nanofiltration for Trace Organic Contaminant Removal: Structure, Solution, and Membrane Fouling Effects on the Rejection of Perfluorochemicals
      Steinle-Darling, Eva; Reinhard, Martin
      Environmental Science & Technology (2008), 42 (14), 5292-5297CODEN: ESTHAG; ISSN:0013-936X. (American Chemical Society)
      The use of nanofiltration (NF) membranes for water recycling requires an improved understanding of the factors that govern rejection of potentially harmful org. trace contaminants. Rejections of 15 perfluorochems. (PFCs), 5 perfluorinated sulfonates, 9 perfluorinated carboxylates, and perfluorooctane sulfonamide (FOSA) by 4 nanofiltration membranes (NF270, NF200, DK, and DL) were measured. Rejections for anionic species were >95% for MW >300 g/mol. FOSA (MW =499 g/mol), which is uncharged at the pH of deionized water (5.6), was rejected as little as 42% (DL membrane). Decreasing the pH to <3 decreases rejection by ≤35%, effectively increasing the MWCO of NF270 by >200 g/mol, while a 2500 mg/L NaCl equiv. increase in ionic strength reduces rejections <1%. An alginate fouling layer increases transmission, where quantifiable, by factors of 4-8. Accumulation of PFCs on membranes was measured after the completion of rejection expts. Based on rejection kinetics and the extent of sorption, we infer that 2 different sorption processes are significant: charged species adsorb quickly to the membrane surface, whereas the uncharged FOSA absorbs within the membrane matrix in a much slower process.
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    13. 13
      Appleman, T. D.; Higgins, C. P.; Quiñones, O.; Vanderford, B. J.; Kolstad, C.; Zeigler-Holady, J. C.; Dickenson, E. R. V. Treatment of poly- and perfluoroalkyl substances in US full-scale water treatment systems. Water Res. 2014, 51, 246– 255,  DOI: 10.1016/j.watres.2013.10.067
      13
      Treatment of poly- and perfluoroalkyl substances in U.S. full-scale water treatment systems
      Appleman, Timothy D.; Higgins, Christopher P.; Quinones, Oscar; Vanderford, Brett J.; Kolstad, Chad; Zeigler-Holady, Janie C.; Dickenson, Eric R. V.
      Water Research (2014), 51 (), 246-255CODEN: WATRAG; ISSN:0043-1354. (Elsevier Ltd.)
      The near ubiquitous presence of poly- and perfluoroalkyl substances (PFASs) in humans has raised concerns about potential human health effects from these chems., some of which are both extremely persistent and bioaccumulative. Because some of these chems. are highly water sol., one major pathway for human exposure is the consumption of contaminated drinking water. This study measured concns. of PFASs in 18 raw drinking water sources and 2 treated wastewater effluents and evaluated 15 full-scale treatment systems for the attenuation of PFASs in water treatment utilities throughout the U.S. A liq.-chromatog. tandem mass-spectrometry method was used to enable measurement of a suite of 23 PFASs, including perfluorocarboxylic acids (PFCAs) and perfluorosulfonic acids (PFSAs). Despite the differences in reporting levels, the PFASs that were detected in >70% of the source water samples (n = 39) included PFSAs, perfluorobutane sulfonic acid (74%), perfluorohexane sulfonic acid (79%), and perfluorooctane sulfonic acid (84%), and PFCAs, perfluoropentanoic acid (74%), perfluorohexanoic acid (79%), perfluoroheptanoic acid (74%), and perfluorooctanoic acid (74%). More importantly, water treatment techniques such as ferric or alum coagulation, granular/micro-/ultra- filtration, aeration, oxidn. (i.e., permanganate, UV/hydrogen peroxide), and disinfection (i.e., ozonation, chlorine dioxide, chlorination, and chloramination) were mostly ineffective in removing PFASs. However, anion exchange and granular activated carbon treatment preferably removed longer-chain PFASs and the PFSAs compared to the PFCAs, and reverse osmosis demonstrated significant removal for all the PFASs, including the smallest PFAS, perfluorobutanoic acid.
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    14. 14
      Sonmez Baghirzade, B.; Zhang, Y.; Reuther, J. F.; Saleh, N. B.; Venkatesan, A. K.; Apul, O. G. Thermal regeneration of spent granular activated carbon presents an opportunity to break the forever PFAS cycle. Environ. Sci. Technol. 2021, 55, 5608– 5619,  DOI: 10.1021/acs.est.0c08224
      14
      Thermal regeneration of spent granular activated carbon presents an opportunity to break the forever PFAS cycle
      Sonmez Baghirzade, Busra; Zhang, Yi; Reuther, James F.; Saleh, Navid B.; Venkatesan, Arjun K.; Apul, Onur G.
      Environmental Science & Technology (2021), 55 (9), 5608-5619CODEN: ESTHAG; ISSN:0013-936X. (American Chemical Society)
      A review. Extensive use of per- and polyfluoroalkyl substances (PFAS) has caused their ubiquitous presence in natural waters. One of the std. practices for PFAS removal from water is adsorption onto granular activated carbon (GAC); however, this approach generates a new waste stream, i.e., PFAS-laden GAC. Considering the recalcitrance of PFAS mols. in the environment, inadequate disposal (e.g., landfill or incineration) of PFAS-laden GAC may let PFAS back into the aquatic cycle. Therefore, developing approaches for PFAS-laden GAC management present unique opportunities to break its forever circulation within the aq. environment. This comprehensive review evaluates the past two decades of research on conventional thermal regeneration of GAC and critically analyzes and summarizes the literature on regeneration of PFAS-laden GACs. Optimized thermal regeneration of PFAS-laden GACs may provide an opportunity to employ existing regeneration infrastructure to mineralize the adsorbed PFAS and recover the spent GAC. The specific objectives of this review are to investigate the role of physicochem. properties of PFAS on thermal regeneration, to assess the changes in regeneration yield as well as GAC phys. and chem. structure upon thermal regeneration, and to critically discuss regeneration parameters controlling the process. This literature review on the engineered regeneration process illustrates the significant promise of this approach that can break the endless environmental cycle of these forever chems., while preserving the desired physicochem. properties of the valuable GAC adsorbent.
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    15. 15
      Liu, S.; Zhao, S.; Liang, Z.; Wang, F.; Sun, F.; Chen, D. Perfluoroalkyl substances (PFASs) in leachate, fly ash, and bottom ash from waste incineration plants: Implications for the environmental release of PFAS. Sci. Total Environ. 2021, 795, 148468,  DOI: 10.1016/j.scitotenv.2021.148468
      15
      Perfluoroalkyl substances (PFASs) in leachate, fly ash, and bottom ash from waste incineration plants: Implications for the environmental release of PFAS
      Liu, Shanshan; Zhao, Shiyi; Liang, Zhihong; Wang, Fei; Sun, Feiyun; Chen, Da
      Science of the Total Environment (2021), 795 (), 148468CODEN: STENDL; ISSN:0048-9697. (Elsevier B.V.)
      Perfluoroalkyl substances (PFASs) are a family of chems. widely distributed in daily use consumer products. Most of these products become municipal solid wastes (MSWs) after they have been used. In the present study, we examd. different types of PFASs in leachate, fly ash and bottom ash produced from three MSW incineration plants in southern China. High PFAS levels were found in leachate (mean concn. 215 ng/mL, range 21.4-682 ng/mL) from the incineration plants, which indicated large amts. of PFASs in the wastes leached out. The av. quantities of PFASs annually discharged from the leachates of the three plants were estd. to be approx. 384 kg (Plant A), 47.3 kg (Plant B), and 2.82 kg (Plant C). Relatively lower levels of PFASs in fly ash (mean 16.4 ng/g, range 1.46-87.6 ng/g) and bottom ash (mean 14.6 ng/g, range 3.11-77.4 ng/g) indicated that high-temp. incineration destroyed most of the PFASs. The wide array of PFASs concns. in all three matrixes illustrated that some PFASs-contg. industrial wastes were still entered into local MSW. In general, short chain PFASs, including perfluorobutyric acid (PFBA) and perfluorobutane sulfonate (PFBS), were the primary PFASs in leachate samples. In addn., PFOS was the predominant PFASs in fly ash samples. The results showed that leachate, fly ash, and bottom ash from MSW incineration plants are important vectors of PFASs.
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    16. 16
      Singh, R. K.; Multari, N.; Nau-Hix, C.; Woodard, S.; Nickelsen, M.; Mededovic Thagard, S.; Holsen, T. M. Removal of poly- and per-fluorinated compounds from ion exchange regenerant still bottom samples in a plasma reactor. Environ. Sci. Technol. 2020, 54, 13973– 13980,  DOI: 10.1021/acs.est.0c02158
      16
      Removal of poly- and per-fluorinated compounds from ion exchange regenerant still bottom samples in a plasma reactor
      Singh, Raj Kamal; Multari, Nicholas; Nau-Hix, Chase; Woodard, Steven; Nickelsen, Michael; Mededovic Thagard, Selma; Holsen, Thomas M.
      Environmental Science & Technology (2020), 54 (21), 13973-13980CODEN: ESTHAG; ISSN:0013-936X. (American Chemical Society)
      "High-concn." and "low-concn." bench-scale batch plasma reactors were used to effectively degrade per- and polyfluoroalkyl substances (PFAS) at a high concn. (~ 100 mg/L) and a low concn. (<1μg/L), resp., in ion exchange (IX) regenerant still bottom (SB) solns. In the SBs, numerous PFAS were detected with a wide concn. range (~ 0.01 to 100 mg/L; total oxidizable precursors (TOP) ~ 4000 to 10000 mg/L). In the "high-concn." plasma reactor, the concns. of PFAS precursors and long-chain perfluoroalkyl acids (PFAAs) (≥6C for PFSAs and ≥8C for perfluorocarboxylic acids (PFCAs)) were decreased by >99.9% in 2 h, and short-chain PFAAs (<6C for perfluorocarboxylic acids (PFSAs) and <8C PFCAs) were decreased by >99% in 6 h of treatment. Subsequently, a "low concn." plasma reactor was used to remove addnl. PFAAs. In this reactor, the addn. of CTAB (cetrimonium bromide, a cationic surfactant) caused short-chain PFAAs, other than PFBA, to be removed to below detection limits in 90 min of treatment time. Overall, >99% of the TOP present in SBs was removed during the treatment. Fluorine recovery of 47 to 117% was obtained in six SB samples. Energy requirement (EE/O) for the treatment of PFOA and PFOS from SBs ranged from 380 to 830 kWh/m3.
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    17. 17
      Qanbarzadeh, M.; Wang, D.; Ateia, M.; Sahu, S. P.; Cates, E. L. Impacts of reactor configuration, degradation mechanisms, and water matrices on perfluorocarboxylic acid treatment efficiency by the UV/Bi3O(OH)(PO4)2 photocatalytic process. ACS ES&T Engg 2021, 1, 239– 248,  DOI: 10.1021/acsestengg.0c00086
      There is no corresponding record for this reference.
    18. 18
      Zhu, Y.; Xu, T.; Zhao, D.; Li, F.; Liu, W.; Wang, B.; An, B. Adsorption and solid-phase photocatalytic degradation of perfluorooctane sulfonate in water using gallium-doped carbon-modified titanate nanotubes. Chem. Eng. J. 2021, 421, 129676,  DOI: 10.1016/j.cej.2021.129676
      18
      Adsorption and solid-phase photocatalytic degradation of perfluorooctane sulfonate in water using gallium-doped carbon-modified titanate nanotubes
      Zhu, Yangmo; Xu, Tianyuan; Zhao, Dongye; Li, Fan; Liu, Wen; Wang, Buhua; An, Byungryul
      Chemical Engineering Journal (Amsterdam, Netherlands) (2021), 421 (Part_1), 129676CODEN: CMEJAJ; ISSN:1385-8947. (Elsevier B.V.)
      Perfluorooctane sulfonate (PFOS) has drawn increasing attention due to its omnipresence and adverse health effects. We prepd. a new adsorptive photocatalyst, Ga/TNTs@AC, based on activated carbon and TiO2, and tested the adsorption and subsequent solid-phase photodegrdn. of PFOS. Ga/TNTs@AC showed faster adsorption kinetics and higher affinity for PFOS than the parent AC, and could degrade 75.0% and mineralize 66.2% of pre-sorbed PFOS within 4-h UV irradn. The efficient PFOS photodegrdn. also regenerates Ga/TNTs@AC, allowing for repeated uses without invoking chem. regenerants. The superior photoactivity is attributed to the oxygen vacancies, which not only suppressed recombination of the e-/h+ pairs, but also facilitated O.-2 generation. Both h+ and O.-2 played crit. roles in the PFOS degrdn., which starts with cleavage of the sulfonate group and converts it into PFOA that is then decarboxylated and defluorinated following the stepwise defluorination mechanism. Ga/TNTs@AC holds the potential for more cost-effective PFOS degrdn.
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    19. 19
      Yang, S.; Fernando, S.; Holsen, T. M.; Yang, Y. Inhibition of perchlorate formation during the electrochemical oxidation of perfluoroalkyl acid in groundwater. Environ. Sci. Technol. Lett. 2019, 6, 775– 780,  DOI: 10.1021/acs.estlett.9b00653
      19
      Inhibition of Perchlorate Formation during the Electrochemical Oxidation of Perfluoroalkyl Acid in Groundwater
      Yang, Shasha; Fernando, Sujan; Holsen, Thomas M.; Yang, Yang
      Environmental Science & Technology Letters (2019), 6 (12), 775-780CODEN: ESTLCU; ISSN:2328-8930. (American Chemical Society)
      Perfluorooctanoic acid (PFOA) and perfluorooctanesulfonate (PFOS) are groundwater contaminants of emerging concern due to their toxicity and persistence. Currently, there are limited destructive treatment options for this type of water. One promising approach is electrochem. oxidn. (EO) using a boron-doped diamond (BDD) anode. However, during EO treatment, chloride in water is readily converted to perchlorate (ClO4-), which is an endocrine disruptor. This is a common dilemma for EO techniques: anodes with higher EO activity tend to produce more ClO4-. In this study, we used the BDD anode as a model anode to treat PFOA and PFOS in a chloride-bearing electrolyte. We found that the formation of ClO4- can be largely inhibited without compromising the efficiency of PFOA and PFOS destruction by adding hydrogen peroxide (≥50 mM H2O2). Exptl. approaches and computational kinetic modeling indicate that H2O2 inhibits ClO4- formation by quenching chlorine and hydroxyl radicals and the oxidn. of PFOA and PFOS is primarily detd. by direct electron transfer oxidn., regardless of the dominant radical species. This facile strategy suppressed 88% of ClO4- formation during EO treatment of groundwater spiked with PFOA and PFOS.
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    20. 20
      Huang, D.; Wang, K.; Niu, J.; Chu, C.; Weon, S.; Zhu, Q.; Lu, J.; Stavitski, E.; Kim, J.-H. Amorphous Pd-loaded Ti4O7 electrode for direct anodic destruction of perfluorooctanoic acid. Environ. Sci. Technol. 2020, 54, 10954– 10963,  DOI: 10.1021/acs.est.0c03800
      20
      Amorphous Pd-loaded Ti4O7 electrode for direct anodic destruction of perfluorooctanoic acid
      Huang, Dahong; Wang, Kaixuan; Niu, Junfeng; Chu, Chiheng; Weon, Seunghyun; Zhu, Qianhong; Lu, Jianjiang; Stavitski, Eli; Kim, Jae-Hong
      Environmental Science & Technology (2020), 54 (17), 10954-10963CODEN: ESTHAG; ISSN:0013-936X. (American Chemical Society)
      We here present a novel Ti4O7-based electrode loaded with amorphous Pd clusters that achieve efficient anodic destruction of perfluorooctanoic acid (PFOA), a persistent water pollutant with significant environmental and human health concerns. These amorphous Pd clusters were characterized by the disordered, noncryst. arrangement of Pd single atoms in close proximity, in contrast to cryst. Pd nanoparticles that have been often employed to tailor the electronic properties of an electrode. We found that the Ti4O7 electrode loaded with amorphous Pd clusters significantly outperformed the Ti4O7 electrode loaded with cryst. Pd particles due to enhanced electron transfer through dominant Pd-O bonds. Combined with the efficient binding of PFOA and its degrdn. intermediates to the fluorinated electrode surface, this electrode was capable of mineralizing PFOA and releasing fluoride as F-. The reaction pathway was found to proceed without involving reactive oxygen species and therefore was not quenched by common anions in complex natural water systems such as chloride ions.
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    21. 21
      Lewis, A. J.; Joyce, T.; Hadaya, M.; Ebrahimi, F.; Dragiev, I.; Giardetti, N.; Yang, J.; Fridman, G.; Rabinovich, A.; Fridman, A. A.; McKenzie, E. R.; Sales, C. M. Rapid degradation of PFAS in aqueous solutions by reverse vortex flow gliding arc plasma. Environ. Sci.: Water Res. Technol. 2020, 6, 1044– 1057,  DOI: 10.1039/c9ew01050e
      21
      Rapid degradation of PFAS in aqueous solutions by reverse vortex flow gliding arc plasma
      Lewis, Asa J.; Joyce, Thomas; Hadaya, Maher; Ebrahimi, Farshad; Dragiev, Ivan; Giardetti, Nickolas; Yang, Junchun; Fridman, Gregory; Rabinovich, Alexander; Fridman, Alexander A.; McKenzie, Erica R.; Sales, Christopher M.
      Environmental Science: Water Research & Technology (2020), 6 (4), 1044-1057CODEN: ESWRAR; ISSN:2053-1419. (Royal Society of Chemistry)
      Poly and perfluoroalkyl substances (PFAS) are a group of fluorinated org. anthropogenic chems. that are resistant to degrdn. In this paper, non-equil., reverse vortex gliding arc plasma (GAP) discharges in air, nitrogen (N2), and pure oxygen (O2) gases were investigated for the removal of perfluoroalkyl carboxylates (PFCA), perfluoroalkyl sulfonates (PFSA), and fluorotelomer sulfonates (FtS) from liq. solns. in a 1-L treatment system. At initial concns. ranging from 0.05 g L-1 to 1 g L-1 significant removal was obsd. for all PFAS compds. by GAP discharges in air, but the degree of degrdn. and defluorination was highly dependent on perfluorinated alkyl chain lengths, with all those contg. 8 or more perfluorinated carbons achieving greater than 90% removal and often greater than 25% defluorination in one hour of treatment time. Following treatment, a fluorine mass balance was attempted for PFOS (58.3% recovery) and PFOA (98.2% recovery) where only a miniscule portion (5.6% and 4.2%) resp. of the degraded PFOS and PFOA were converted to quantifiable PFAS, while the rest of the fluorine may leave as gaseous species or non-quantifiable PFAS. The non-equil. GAP discharge used in this study was found to use similar amts. of energy to other studies using non-equil. plasma (150 kJ L-1 to 1000 kJ L-1), which is approx. three to twenty times less than the amt. of energy used to evap. water (∼3000 kJ L-1). Assuming pseudo-first-order kinetics, the figure-of-merit elec. energy per order (EEo) values were calcd. to est. the energy efficiency of the system. The lowest EEo for PFOS was 23.2 kW h m-3 per order and 213.4 kW h m-3 per order for PFOA, similar with existing technologies (which range from 10 to 10 000 kW h m-3 per order). These results indicate that non-thermal air plasma discharges are promising technologies for treatment of PFAS that should be further researched and developed.
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      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3cXhvFKhsb8%253D&md5=845ca70ef7c9cacd42414d0bf970bda2
    22. 22
      Saleem, M.; Biondo, O.; Sretenović, G.; Tomei, G.; Magarotto, M.; Pavarin, D.; Marotta, E.; Paradisi, C. Comparative performance assessment of plasma reactors for the treatment of PFOA; reactor design, kinetics, mineralization and energy yield. Chem. Eng. J. 2020, 382, 123031,  DOI: 10.1016/j.cej.2019.123031
      22
      Comparative performance assessment of plasma reactors for the treatment of PFOA; reactor design, kinetics, mineralization and energy yield
      Saleem, Mubbshir; Biondo, Omar; Sretenovic, Goran; Tomei, Giulia; Magarotto, Mirko; Pavarin, Daniele; Marotta, Ester; Paradisi, Cristina
      Chemical Engineering Journal (Amsterdam, Netherlands) (2020), 382 (), 123031CODEN: CMEJAJ; ISSN:1385-8947. (Elsevier B.V.)
      The development of efficient plasma-based technologies for water treatment in general and decontamination from perfluoroalkyl substances, in particular, is a timely and challenging research topic. This study investigated the degrdn. of PFOA (perfluorooctanoic acid) in water using three reactors with different configurations and implementing different plasma regimes. Two reactors were available from previous studies on other recalcitrant pollutants and use, resp., corona discharge and plasma in gas bubbles. The third reactor was designed and developed for this specific application and uses a self-pulsing streamer discharge (SPD) over the liq. surface. The performance of the three reactors was assessed and compared using air as plasma feed gas and a PFOA soln. (41.4 mg/L) in Milli-Q-water. The SPD reactor was found to be the most efficient in terms of energy efficiency and PFOA conversion and degrdn. rate. It was therefore further tested and characterized by studying the effects of changing the aq. media in which PFOA was dissolved (Milli-Q and tap water) and the plasma feed gas (synthetic air, ambient air and argon). Due to the formation of nitrous and nitric acids, esp. for plasma generated in ambient and synthetic air, the soln. pH, cond., and hence the plasma input power changed significantly during the expts. The best results were obtained using argon for plasma inception and PFOA solns. in tap water: the energy efficiency and fluoride recovery were 561 mg/kWh and 47%, resp.
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    23. 23
      Singh, R. K.; Brown, E.; Thagard, S. M.; Holsen, T. M. Treatment of PFAS-containing landfill leachate using an enhanced contact plasma reactor. J. Hazard. Mater. 2021, 408, 124452,  DOI: 10.1016/j.jhazmat.2020.124452
      23
      Treatment of PFAS-containing landfill leachate using an enhanced contact plasma reactor
      Singh, Raj Kamal; Brown, Elizabeth; Mededovic Thagard, Selma; Holsen, Thomas M.
      Journal of Hazardous Materials (2021), 408 (), 124452CODEN: JHMAD9; ISSN:0304-3894. (Elsevier B.V.)
      A bench-scale plasma reactor was used to degrade poly- and perfluoroalkyl substances (PFAS) in landfill leachate samples obtained from three different locations. In the leachate samples before treatment, five long-chain, six short-chain perfluoroalkyl acids (PFAAs) and eight PFAA precursors were detected in a wide concn. range (∼102 to 105 ng/L; total oxidizable precursors (TOP) ∼106 ng/L). The concn. of perfluorooctane sulfonate (PFOS) plus perfluorooctanoic acid (PFOA) ranged between 2000 and 3000 ng/L. Plasma-based water treatment of 500 mL samples resulted in faster removal rates for longer-chain than shorter chain length PFAAs. Both PFOS and PFOA were removed to below United States Environmental Protection Agency's (USEPA's) health advisory concn. level (HAL) concns. (<70 ng/L) in 10-75 min; 90% PFOA and PFOS removal was achieved in 10 min. Long-chain and short-chain PFAAs were removed by >99.9% and 10-99.9%, resp. The removal rate const. (kPFOA+PFOS) for combined PFOA and PFOS ranged between 0.20 and 0.34 min-1. Overall, 60 ± 2% of the TOP concn. and 34 ± 2% of the TOC were removed. No effect of non-PFAS co-contaminants (e.g., total initial org. carbon concn. ∼2000 mg/L) on the degrdn. efficiency was obsd. Short-chain PFAA removal efficacy was enhanced by adding a cationic surfactant (cetrimonium bromide). Overall, the results indicate that plasma-based technol. may be a viable technol. for the treatment of PFAS-contaminated landfill leachates.
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    24. 24
      Huang, L.; Dong, W.; Hou, H. Investigation of the reactivity of hydrated electron toward perfluorinated carboxylates by laser flash photolysis. Chem. Phys. Lett. 2007, 436, 124– 128,  DOI: 10.1016/j.cplett.2007.01.037
      24
      Investigation of the reactivity of hydrated electron toward perfluorinated carboxylates by laser flash photolysis
      Huang, Li; Dong, Wenbo; Hou, Huiqi
      Chemical Physics Letters (2007), 436 (1-3), 124-128CODEN: CHPLBC; ISSN:0009-2614. (Elsevier B.V.)
      Laser flash photolysis technique was employed to investigate the reactivity of hydrated electron (e-aq) toward a series of perfluorinated carboxylates, CnF2n+1COO- (n = 1, 3, 7), at 288 ± 1 K in aq. phase. It was demonstrated that the length of -CnF2n+1 group exerted substantial influence on the rate const. The second-order rate consts. for e-aq with CF3COO-, C3F7COO-, C7F15COO- were estd. to be (1.9 ± 0.2) × 106 M-1 s-1 (μ = 0), (7.1 ± 0.3) × 106 M-1 s-1 (μ = 0) and (1.7 ± 0.5) × 107 M-1 s-1 (μ = 0.01 M), resp.
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    25. 25
      Park, H.; Vecitis, C. D.; Cheng, J.; Choi, W.; Mader, B. T.; Hoffmann, M. R. Reductive defluorination of aqueous perfluorinated alkyl surfactants: Effects of ionic headgroup and chain length. J. Phys. Chem. A 2009, 113, 690– 696,  DOI: 10.1021/jp807116q
      25
      Reductive Defluorination of Aqueous Perfluorinated Alkyl Surfactants: Effects of Ionic Headgroup and Chain Length
      Park, Hyunwoong; Vecitis, Chad D.; Cheng, Jie; Choi, Wonyong; Mader, Brian T.; Hoffmann, Michael R.
      Journal of Physical Chemistry A (2009), 113 (4), 690-696CODEN: JPCAFH; ISSN:1089-5639. (American Chemical Society)
      Perfluorinated chems. (PFCs) are distributed throughout the environment. In the case of perfluorinated alkyl carboxylates and sulfonates, they can be classified as persistent org. pollutants since they are resistant to environmentally relevant redn., oxidn., and hydrolytic processes. With this in mind, we report on the reductive defluorination of perfluorobutanoate, PFBA (C3F7CO2-), perfluorohexanoate, PFHA (C5F11CO2-), perfluorooctanoate, PFOA (C7F15CO2-), perfluorobutane sulfonate, PFBS (C4F9SO3-), perfluorohexane sulfonate, PFHS (C6F13SO3-), and perfluorooctane sulfonate, PFOS (C8F17SO3-) by aquated electrons, eaq-, that are generated from the UV photolysis (λ = 254 nm) of iodide. The ionic headgroup (-SO3- vs -CO2-) has a significant effect on the redn. kinetics and extent of defluorination (F index = -[F-]produced/[PFC]degraded). Perfluoroalkylsulfonate redn. kinetics and the F index increase linearly with increasing chain length. In contrast, perfluoroalkylcarboxylate chain length appears to have a negligible effect on the obsd. kinetics and the F index. H/F ratios in the gaseous fluoro-org. products are consistent with measured F indexes. Incomplete defluorination of the gaseous products suggests a reductive cleavage of the ionic headgroup occurs before complete defluorination. Detailed mechanisms involving initiation by aquated electrons are proposed.
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    26. 26
      Song, Z.; Tang, H.; Wang, N.; Zhu, L. Reductive defluorination of perfluorooctanoic acid by hydrated electrons in a sulfite-mediated UV photochemical system. J. Hazard. Mater. 2013, 262, 332– 338,  DOI: 10.1016/j.jhazmat.2013.08.059
      26
      Reductive defluorination of perfluorooctanoic acid by hydrated electrons in a sulfite-mediated UV photochemical system
      Song, Zhou; Tang, Heqing; Wang, Nan; Zhu, Lihua
      Journal of Hazardous Materials (2013), 262 (), 332-338CODEN: JHMAD9; ISSN:0304-3894. (Elsevier B.V.)
      A method for reductive degrdn. of perfluorooctanoic acid (PFOA) was established by using a sulfite/UV process. This process led to a PFOA removal of 100% at ∼1 h and a defluorination ratio of 88.5% at reaction time of 24 h under N2 atmosphere, whereas the use of either UV irradn. or SO32- alone induced little defluorination of PFOA under the same conditions. The reductive defluorination of PFOA was achieved by hydrated electrons being generated from the photo-conversion of SO32- as a mediator. Theor. reaction kinetic anal. demonstrated that the generation of hydrated electrons was promoted by increasing either SO32- concn. or soln. pH, leading to the acceleration of the PFOA defluorination. Accompanying the redn. of PFOA, a small amt. of short-chain perfluorocarboxylic acids, less fluorinated carboxylic acids and perfluorinated alkyl sulfonates were generated, all of which were able to be further degraded with further releasing of F- ions. Based on the generation, accumulation and distribution of intermediates, hydrated electrons induced defluorination pathway of PFOA was proposed in a sulfite-mediated UV photochem. system.
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    27. 27
      Tian, H.; Gao, J.; Li, H.; Boyd, S. A.; Gu, C. Complete defluorination of perfluorinated compounds by hydrated electrons generated from 3-indole-acetic-acid in organomodified montmorillonite. Sci. Rep. 2016, 6, 32949,  DOI: 10.1038/srep32949
      27
      Complete Defluorination of Perfluorinated Compounds by Hydrated Electrons Generated from 3-Indole-acetic-acid in Organomodified Montmorillonite
      Tian, Haoting; Gao, Juan; Li, Hui; Boyd, Stephen A.; Gu, Cheng
      Scientific Reports (2016), 6 (), 32949CODEN: SRCEC3; ISSN:2045-2322. (Nature Publishing Group)
      Here we describe a unique process that achieves complete defluorination and decompn. of perfluorinated compds. (PFCs) which comprise one of the most recalcitrant and widely distributed classes of toxic pollutant chems. found in natural environments. Photogenerated hydrated electrons derived from 3-indole-acetic-acid within an organomodified clay induce the reductive defluorination of co-sorbed PFCs. The process proceeds to completion within a few hours under mild reaction conditions. The organomontmorillonite clay promotes the formation of highly reactive hydrated electrons by stabilizing indole radical cations formed upon photolysis, and prevents their deactivation by reaction with protons or oxygen. In the constrained interlayer regions of the clay, hydrated electrons and co-sorbed PFCs are brought in close proximity thereby increasing the probability of reaction. This novel green chem. provides the basis for in situ and ex situ technologies to treat one of the most troublesome, recalcitrant and ubiquitous classes of environmental contaminants, i.e., PFCs, utilizing innocuous reagents, naturally occurring materials and mild reaction conditions.
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    28. 28
      Sun, Z.; Zhang, C.; Xing, L.; Zhou, Q.; Dong, W.; Hoffmann, M. R. UV/nitrilotriacetic acid process as a novel strategy for efficient photoreductive degradation of perfluorooctanesulfonate. Environ. Sci. Technol. 2018, 52, 2953– 2962,  DOI: 10.1021/acs.est.7b05912
      28
      UV/nitrilotriacetic acid process as a novel strategy for efficient photoreductive degradation of perfluorooctanesulfonate
      Sun, Zhuyu; Zhang, Chaojie; Xing, Lu; Zhou, Qi; Dong, Wenbo; Hoffmann, Michael R.
      Environmental Science & Technology (2018), 52 (5), 2953-2962CODEN: ESTHAG; ISSN:0013-936X. (American Chemical Society)
      Perfluorooctanesulfonate (PFOS) is a toxic, bioaccumulative, and highly persistent anthropogenic chem. Hydrated electrons (eaq-) are potent nucleophiles that can effectively decomp. PFOS. In previous studies, eaq- are mainly produced by photoionization of aq. anions or arom. compds. In this study, we proposed a new photolytic strategy to generate eaq- and in turn decomp. PFOS, which utilizes nitrilotriacetic acid (NTA) as a photosensitizer to induce water photodissocn. and photoionization, and subsequently as a scavenger of hydroxyl radical (•OH) to minimize the geminate recombination between •OH and eaq-. The net effect is to increase the amt. of eaq- available for PFOS degrdn. The UV/NTA process achieved a high PFOS degrdn. ratio of 85.4% and a defluorination ratio of 46.8% within 10 h. A pseudo-first-order rate const. (k) of 0.27 h-1 was obtained. The laser flash photolysis study indicates that eaq- is the dominant reactive species responsible for PFOS decompn. The generation of eaq- is greatly enhanced and its half-life is significantly prolonged in the presence of NTA. The ESR measurement verified the photodissocn. of water by detecting •OH. The model compd. study indicates that the acetate and amine groups are the primary reactive sites.
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    29. 29
      Bentel, M. J.; Yu, Y.; Xu, L.; Li, Z.; Wong, B. M.; Men, Y.; Liu, J. Defluorination of per- and polyfluoroalkyl substances (PFASs) with hydrated electrons: Structural dependence and implications to PFAS remediation and management. Environ. Sci. Technol. 2019, 53, 3718– 3728,  DOI: 10.1021/acs.est.8b06648
      29
      Defluorination of Per- and Polyfluoroalkyl Substances (PFASs) with Hydrated Electrons: Structural Dependence and Implications to PFAS Remediation and Management
      Bentel, Michael J.; Yu, Yaochun; Xu, Lihua; Li, Zhong; Wong, Bryan M.; Men, Yujie; Liu, Jinyong
      Environmental Science & Technology (2019), 53 (7), 3718-3728CODEN: ESTHAG; ISSN:0013-936X. (American Chemical Society)
      This study investigates crit. structure-reactivity relationships within 34 representative per- and polyfluoroalkyl substances (PFASs) undergoing defluorination with UV-generated hydrated electrons. While CnF2n+1-COO- with variable fluoroalkyl chain lengths (n = 2 to 10) exhibited a similar rate and extent of parent compd. decay and defluorination, the reactions of telomeric CnF2n+1-CH2CH2-COO- and CnF2n+1-SO3- showed an apparent dependence on the length of the fluoroalkyl chain. Cross comparison of exptl. results, including different rates of decay and defluorination of specific PFAS categories, the incomplete defluorination from most PFAS structures, and the surprising 100% defluorination from CF3COO-, leads to the elucidation of new mechanistic insights into PFAS degrdn. Theor. calcns. on the C-F bond dissocn. energies (BDEs) of all PFAS structures reveal strong relationships among (i) the rate and extent of decay and defluorination, (ii) head functional groups, (iii) fluoroalkyl chain length, and (iv) the position and no. of C-F bonds with low BDEs. These relationships are further supported by the spontaneous cleavage of specific bonds during calcd. geometry optimization of PFAS structures bearing one extra electron, and by the product analyses with high-resoln. mass spectrometry. Multiple reaction pathways, including H/F exchange, dissocn. of terminal functional groups, and decarboxylation-triggered HF elimination and hydrolysis, result in the formation of variable defluorination products. The selectivity and ease of C-F bond cleavage highly depends on mol. structures. These findings provide crit. information for developing PFAS treatment processes and technologies to destruct a wide scope of PFAS pollutants and for designing fluorochem. formulations to avoid releasing recalcitrant PFASs into the environment.
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    30. 30
      Cui, J.; Gao, P.; Deng, Y. Destruction of per- and polyfluoroalkyl substances (PFAS) with advanced reduction processes (ARPs): A critical review. Environ. Sci. Technol. 2020, 54, 3752– 3766,  DOI: 10.1021/acs.est.9b05565
      30
      Destruction of Per- and Polyfluoroalkyl Substances (PFAS) with Advanced Reduction Processes (ARPs): A Critical Review
      Cui, Junkui; Gao, Panpan; Deng, Yang
      Environmental Science & Technology (2020), 54 (7), 3752-3766CODEN: ESTHAG; ISSN:0013-936X. (American Chemical Society)
      A review. Advanced redn. processes (ARPs) have emerged as a promising method for destruction of persistent per- and polyfluoroalkyl substances (PFAS) in H2O due to the generation of short-lived and highly reductive hydrated electrons (eaq-). This study provides a crit. review on the mechanisms and performance of reductive destruction of PFAS with eaq-. Unique properties of eaq- and its generation in different ARP systems, particularly UV/sulfite and UV/iodide, are overviewed. Different degrdn. mechanisms of PFAS chems., such as perfluorooctanoic acid (PFOA), perfluorooctanesulfonate (PFOS), and others (e.g., short chain perfluorocarboxylic acids (PFCAs) and perfluorosulfonic acids (PFSAs), per- and polyfluoro dicarboxylic acids, and fluorotelomer carboxylic acids), are reviewed, discussed, and compared. The degrdn. pathways of these PFAS chems. rely heavily upon their head groups. For specific PFAS types, fluoroalkyl chain lengths may also affect their reductive degrdn. patterns. Degrdn. and defluorination efficiencies of PFAS are considerably influenced by soln. chem. parameters and operating factors, such as pH, dose of chem. solute (i.e., sulfite or iodide) for eaq- photoprodn., dissolved O, humic acid, nitrate, and temp. Also, implications of the state-of-the-art knowledge on practical PFAS control actions in H2O industries are discussed and the priority research needs are identified.
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    31. 31
      Bao, Y.; Huang, J.; Cagnetta, G.; Yu, G. Removal of F–53B as PFOS alternative in chrome plating wastewater by UV/sulfite reduction. Water Res. 2019, 163, 114907,  DOI: 10.1016/j.watres.2019.114907
      31
      Removal of F-53B as PFOS alternative in chrome plating wastewater by UV/Sulfite reduction
      Bao, Yixiang; Huang, Jun; Cagnetta, Giovanni; Yu, Gang
      Water Research (2019), 163 (), 114907CODEN: WATRAG; ISSN:0043-1354. (Elsevier Ltd.)
      Chrome mist suppressants are key chems. used in the chrome plating industry to reduce exposure of workers by inhalation to airborne chromic acid pollution. Perfluoroalkyl sulfonated compds. are excellent mist suppressants, thanks to their chem. stability and surface activity. Therefore, despite mounting evidence for their persistence, bioaccumulation and toxicity, it is likely that such chems. will continue to be used for the foreseeable future because of their importance and lack of alternatives. The present study is aimed at assessing the feasibility of advanced redn. as an effective technol. to treat chrome plating industry wastewater. In particular, wastewater contg. a chlorinated polyfluorinated ether sulfonate (i.e. F-53B), an alternative to perfluorooctanesulfonate (PFOS) used to prep. chrome mist suppressant in China, was treated by UV-activated sulfite. Results demonstrates that in ultrapure water F-53B can be easily degraded within 1 min-much faster than PFOS. Stoichiometric fluoride recovery was also achieved, confirming significant defluorination of the pollutant. Such superior reducibility was due to the presence of chlorine atoms, as corroborated by quantum chem. calcns. F-53B degrdn. was also achieved in chrome plating industrial wastewater, which yielded results were slower than those achieved in the lab. nonetheless obtained complete abatement within 60 min. These results suggest that the proposed advanced redn. process is one of the safest options to control PFAS discharge in the environment and reduce the related risks to ecosystems.
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    32. 32
      Bentel, M. J.; Yu, Y.; Xu, L.; Kwon, H.; Li, Z.; Wong, B. M.; Men, Y.; Liu, J. Degradation of perfluoroalkyl ether carboxylic acids with hydrated electrons: Structure-reactivity relationships and environmental implications. Environ. Sci. Technol. 2020, 54, 2489– 2499,  DOI: 10.1021/acs.est.9b05869
      32
      Degradation of Perfluoroalkyl Ether Carboxylic Acids with Hydrated Electrons: Structure-Reactivity Relationships and Environmental Implications
      Bentel, Michael J.; Yu, Yaochun; Xu, Lihua; Kwon, Hyuna; Li, Zhong; Wong, Bryan M.; Men, Yujie; Liu, Jinyong
      Environmental Science & Technology (2020), 54 (4), 2489-2499CODEN: ESTHAG; ISSN:0013-936X. (American Chemical Society)
      This study explores structure-reactivity relationships for the degrdn. of emerging perfluoroalkyl ether carboxylic acid (PFECA) pollutants with UV-generated hydrated electrons (eaq-). The rate and extent of PFECA degrdn. depend on both the branching extent and the chain length of oxygen-segregated fluoroalkyl moieties. Kinetic measurements, theor. calcns., and transformation product analyses provide a comprehensive understanding of the PFECA degrdn. mechanisms and pathways. In comparison to traditional full-carbon-chain perfluorocarboxylic acids, the distinct degrdn. behavior of PFECAs is attributed to their ether structures. The ether oxygen atoms increase the bond dissocn. energy of the C-F bonds on the adjacent -CF2- moieties. This impact reduces the formation of H/F-exchanged polyfluorinated products that are recalcitrant to reductive defluorination. Instead, the cleavage of ether C-O bonds generates unstable perfluoroalcs. and thus promotes deep defluorination of short fluoroalkyl moieties. In comparison to linear PFECAs, branched PFECAs have a higher tendency of H/F exchange on the tertiary carbon and thus lower percentages of defluorination. These findings provide mechanistic insights for an improved design and efficient degrdn. of fluorochems.
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    33. 33
      Chen, Z.; Li, C.; Gao, J.; Dong, H.; Chen, Y.; Wu, B.; Gu, C. Efficient reductive destruction of perfluoroalkyl substances under self-assembled micelle confinement. Environ. Sci. Technol. 2020, 54, 5178– 5185,  DOI: 10.1021/acs.est.9b06599
      33
      Efficient Reductive Destruction of Perfluoroalkyl Substances under Self-Assembled Micelle Confinement
      Chen, Zhanghao; Li, Chen; Gao, Juan; Dong, Hailiang; Chen, Yi; Wu, Bing; Gu, Cheng
      Environmental Science & Technology (2020), 54 (8), 5178-5185CODEN: ESTHAG; ISSN:0013-936X. (American Chemical Society)
      Recently, perfluoroalkyl substances (PFASs) have received great attention from both academia and the industry due to their persistence and health risks. Here, we developed a simple ternary self-assembled micelle composite, consisting of a photosensitive substance (indole HOAc, IAA), cationic surfactant (cetyltrimethylammonium bromide), and contaminant (PFAS). Owing to the rapid hydrated electron transfer from IAA to the PFAS in the micelle, the PFAS degrdn. and defluorination were greatly enhanced even under ambient conditions. After 2.5 h UV irradn., the perfluorooctanoic acid (PFOA) concn. decreased from 10 mg L-1 to ∼60 ng L-1, which is below the drinking H2O health advisory level of the United States Environmental Protection Agency for the combined concn. of PFOA and perfluorooctane sulfonate (70 ng L-1). Meanwhile, the dissolved org. C content of the reaction soln. was also reduced to ∼3 mg L-1 due to the quick settlement and automatic sepn. of the micelle. Also, the newly developed composite was also adaptable to a wide pH range (pH 4-8), attributing to the barrier created by the ternary micelle system. This novel self-assembly method is expected to directly treat industrial PFAS-contg. wastewater or PFAS-enriched concs. derived from adsorption processes. The conceptually new advanced redn. technique represents a major breakthrough toward PFAS rapid destruction and efficient usage of hydrated electrons and might also shed light on other environmental applications.
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    34. 34
      Chen, Z.; Teng, Y.; Mi, N.; Jin, X.; Yang, D.; Wang, C.; Wu, B.; Ren, H.; Zeng, G.; Gu, C. Highly efficient hydrated electron utilization and reductive destruction of perfluoroalkyl substances induced by intermolecular interaction. Environ. Sci. Technol. 2021, 55, 3996– 4006,  DOI: 10.1021/acs.est.0c07927
      34
      Highly efficient hydrated electron utilization and reductive destruction of perfluoroalkyl substances induced by intermolecular interaction
      Chen, Zhanghao; Teng, Ying; Mi, Na; Jin, Xin; Yang, Deshuai; Wang, Chao; Wu, Bing; Ren, Hongqiang; Zeng, Guixiang; Gu, Cheng
      Environmental Science & Technology (2021), 55 (6), 3996-4006CODEN: ESTHAG; ISSN:0013-936X. (American Chemical Society)
      Perfluoroalkyl substances (PFASs) are highly toxic synthetic chems., which are considered the most persistent org. contaminants in the environment. Previous studies have demonstrated that hydrated electron based techniques could completely destruct these compds. However, in the reactions, alk. and anaerobic conditions are generally required or surfactants are involved. Herein, we developed a simple binary composite, only including PFAS and hydrated electron source chem. The system exhibited high efficiency for the utilization of hydrated electrons to decomp. PFASs. By comparing the degrdn. processes of perfluorooctanoic acid (PFOA) in the presence of seven indole derivs. with different chem. properties, we could conclude that the reaction efficiency was dependent on not only the yield of hydrated electrons but also the interaction between PFOA and indole deriv. Among these derivs., indole showed the highest degrdn. performance due to its relatively high ability to generate hydrated electrons, and more importantly, indole could form a hydrogen bonding with PFOA to accelerate the electron transfer. Moreover, the novel composite demonstrated high reaction efficiency even with coexisting humic substance and in a wide pH range (4-10). This study would deepen our understanding of the design of hydrated electron based techniques to treat PFAS-contg. wastewater.
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    35. 35
      Huang, C.; Linkous, C. A.; Adebiyi, O.; T-Raissi, A. Hydrogen production via photolytic oxidation of aqueous sodium sulfite solutions. Environ. Sci. Technol. 2010, 44, 5283– 5288,  DOI: 10.1021/es903766w
      35
      Hydrogen Production via Photolytic Oxidation of Aqueous Sodium Sulfite Solutions
      Huang, Cunping; Linkous, Clovis A.; Adebiyi, Olawale; T-Raissi, Ali
      Environmental Science & Technology (2010), 44 (13), 5283-5288CODEN: ESTHAG; ISSN:0013-936X. (American Chemical Society)
      Sulfur dioxide (SO2) emission from coal-burning power plants and refinery operations has been implicated as a cause of acid rain and other air pollution related problems. The conventional treatment of SO2-contaminated air consists of two steps: SO2 absorption using an aq. sodium hydroxide soln., forming aq. sodium sulfite (Na2SO3), and Na2SO3 oxidn. via air purging to produce sodium sulfate (Na2SO4). In this process, the potential energy of SO2 is lost. This paper presents a novel UV photolytic process for prodn. of hydrogen from aq. Na2SO3 solns. The results show that the quantum efficiency of hydrogen prodn. can reach 14.4% under illumination from a low pressure mercury lamp. The mechanism occurs via two competing reaction pathways that involve oxidn. of SO32- to SO42- directly and through the dithionate (S2O62-) ion intermediate. The first route becomes dominant once a photostationary state for S2O62- is established. The initial pH of Na2SO3 soln. plays an important role in detg. both the hydrogen prodn. rate and the final products of the photolytic oxidn. At initial soln. pH of 9.80 Na2SO3 photooxidn. generates Na2SO4 as the final reaction product, while Na2S2O6 is merely a reaction intermediate. The highest hydrogen prodn. rate occurs when the initial soln. pH is 7.55. Redn. in the initial soln. pH to 5.93 results in disproportionation of HSO3- to elemental sulfur and SO42- but no hydrogen prodn.
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    36. 36
      Li, X.; Ma, J.; Liu, G.; Fang, J.; Yue, S.; Guan, Y.; Chen, L.; Liu, X. Efficient reductive dechlorination of monochloroacetic acid by sulfite/UV process. Environ. Sci. Technol. 2012, 46, 7342– 7349,  DOI: 10.1021/es3008535
      36
      Efficient Reductive Dechlorination of Monochloroacetic Acid by Sulfite/UV Process
      Li, Xuchun; Ma, Jun; Liu, Guifang; Fang, Jingyun; Yue, Siyang; Guan, Yinghong; Chen, Liwei; Liu, Xiaowei
      Environmental Science & Technology (2012), 46 (13), 7342-7349CODEN: ESTHAG; ISSN:0013-936X. (American Chemical Society)
      Most halogenated org. compds. (HOCs) are toxic and persistent, and their efficient destruction is currently a challenge. We propose a sulfite/UV (253.7 nm) process to eliminate HOCs. Monochloroacetic acid (MCAA) was selected as the target compd. and was degraded rapidly in the sulfite/UV process. The degrdn. kinetics were accelerated proportionally to the increased sulfite concn., while the significant enhancement by increasing pH only occurred at pH 6.0-8.7. The degrdn. proceeded via a reductive dechlorination mechanism induced by hydrated electron (eaq-), and complete dechlorination was readily achieved with almost all the Cl atoms in MCAA released as chlorides. Mass balance (C and Cl) studies showed that acetate, succinate, sulfoacetate, and chloride were the major products. A degrdn. pathway is proposed. The dual roles of pH were not only to regulate the S(IV) species distribution but also to control the interconversion between eaq- and H·. Effective quantum efficiency (Φ) for the formation of eaq- in the process was detd. to be 0.116±0.002 mol/einstein. This study may provide a promising alternative for complete dehalogenation of most HOCs and reductive detoxification of numerous toxicants.
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    37. 37
      Bentel, M. J.; Liu, Z.; Yu, Y.; Gao, J.; Men, Y.; Liu, J. Enhanced degradation of perfluorocarboxylic acids (PFCAs) by UV/sulfite treatment: Reaction mechanisms and system efficiencies at pH 12. Environ. Sci. Technol. Lett. 2020, 7, 351– 357,  DOI: 10.1021/acs.estlett.0c00236
      37
      Enhanced Degradation of Perfluorocarboxylic Acids (PFCA) by UV/Sulfite Treatment: Reaction Mechanisms and System Efficiencies at pH 12
      Bentel, Michael J.; Liu, Zekun; Yu, Yaochun; Gao, Jinyu; Men, Yujie; Liu, Jinyong
      Environmental Science & Technology Letters (2020), 7 (5), 351-357CODEN: ESTLCU; ISSN:2328-8930. (American Chemical Society)
      Reductive defluorination with UV-generated, hydrated electrons (eaq-) is a promising technol. to destroy perfluorocarboxylic acids (PFCA, CnF2n+1COO-); however, previous studies at pH 9-10 displayed a slow reaction rate, limited defluorination percentage (deF%), and high energy consumption. A substantially enhanced rate and extent of PFCA defluorination by operating a UV/sulfite system at optimized pH 12 are reported. Degrdn. kinetics and transformation products showed that at pH 12, eaq- cleaved multiple strong C-F bonds where were not cleaved at pH 9.5. The high pH condition also significantly favored the preferred decarboxylation pathway for deep defluorination. Compared to reactions at pH 9.5, an increase in soln. pH to 12 improved UV lamp energy efficiency 5 to 22-fold, enhanced C3-9 PFCA deF% to 73-93%, and reduced overall chem. consumption.
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    38. 38
      Liu, Z.; Bentel, M. J.; Yu, Y.; Ren, C.; Gao, J.; Pulikkal, V. F.; Sun, M.; Men, Y.; Liu, J. Near-quantitative defluorination of perfluorinated and fluorotelomer carboxylates and sulfonates with integrated oxidation and reduction. Environ. Sci. Technol. 2021, 55, 7052– 7062,  DOI: 10.1021/acs.est.1c00353
      38
      Near-quantitative defluorination of perfluorinated and fluorotelomer carboxylates and sulfonates with integrated oxidation and reduction
      Liu, Zekun; Bentel, Michael J.; Yu, Yaochun; Ren, Changxu; Gao, Jinyu; Pulikkal, Vivek Francis; Sun, Mei; Men, Yujie; Liu, Jinyong
      Environmental Science & Technology (2021), 55 (10), 7052-7062CODEN: ESTHAG; ISSN:0013-936X. (American Chemical Society)
      The UV-sulfite reductive treatment using hydrated electrons (eaq-) is a promising technol. for destroying perfluorocarboxylates (PFCAs, CnF2n+1COO-) in any chain length. However, the C-H bonds formed in the transformation products strengthen the residual C-F bonds and thus prevent complete defluorination. Reductive treatments of fluorotelomer carboxylates (FTCAs, CnF2n+1-CH2CH2-COO-) and sulfonates (FTSAs, CnF2n+1-CH2CH2-SO3-) are also sluggish because the ethylene linker separates the fluoroalkyl chain from the end functional group. In this work, we used oxidn. (Ox) with hydroxyl radicals (HO•) to convert FTCAs and FTSAs to a mixt. of PFCAs. This process also cleaved 35-95% of C-F bonds depending on the fluoroalkyl chain length. We probed the stoichiometry and mechanism for the oxidative defluorination of fluorotelomers. The subsequent redn. (Red) with UV-sulfite achieved deep defluorination of the PFCA mixt. for up to 90%. The following use of HO• to oxidize the H-rich residues led to the cleavage of the remaining C-F bonds. We examd. the efficacy of integrated oxidative and reductive treatment of n = 1-8 PFCAs, n = 4,6,8 perfluorosulfonates (PFSAs, CnF2n+1-SO3-), n = 1-8 FTCAs, and n = 4,6,8 FTSAs. A majority of structures yielded near-quant. overall defluorination (97-103%), except for n = 7,8 fluorotelomers (85-89%), n = 4 PFSA (94%), and n = 4 FTSA (93%). The results show the feasibility of complete defluorination of legacy PFAS pollutants and will advance both remediation technol. design and water sample anal.
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    39. 39
      Park, H.; Vecitis, C. D.; Cheng, J.; Dalleska, N. F.; Mader, B. T.; Hoffmann, M. R. Reductive degradation of perfluoroalkyl compounds with aquated electrons generated from iodide photolysis at 254 nm. Photochem. Photobiol. Sci. 2011, 10, 1945– 1953,  DOI: 10.1039/c1pp05270e
      39
      Reductive degradation of perfluoroalkyl compounds with aquated electrons generated from iodide photolysis at 254 nm
      Park, Hyunwoong; Vecitis, Chad D.; Cheng, Jie; Dalleska, Nathan F.; Mader, Brian T.; Hoffmann, Michael R.
      Photochemical & Photobiological Sciences (2011), 10 (12), 1945-1953CODEN: PPSHCB; ISSN:1474-905X. (Royal Society of Chemistry)
      The perfluoroalkyl compds. (PFCs), perfluoroalkyl sulfonates (PFXS) and perfluoroalkyl carboxylates (PFXA) are environmentally persistent and recalcitrant towards most conventional water treatment technologies. Here, we complete an in depth examn. of the UV-254 nm prodn. of aquated electrons during iodide photolysis for the reductive defluorination of six aquated perfluoroalkyl compds. (PFCs) of various headgroup and perfluorocarbon tail length. Cyclic voltammograms (CV) show that a potential of +2.0 V (vs. NHE) is required to induce PFC oxidn. and -1.0 V is required to induce PFC redn. indicating that PFC redn. is the thermodynamically preferred process. However, PFCs are obsd. to degrade faster during UV(254 nm)/persulfate (S2O82-) photolysis yielding sulfate radicals (E° = +2.4 V) as compared to UV(254 nm)/iodide (I-) photolysis yielding aquated electrons (E° = -2.9 V). Aquated electron scavenging by photoproduced triiodide (I3-), which achieved a steady-state concn. proportional to [PFOS]0, reduces the efficacy of the UV/iodide system towards PFC degrdn. PFC photoredn. kinetics are obsd. to be dependent on PFC headgroup, perfluorocarbon chain length, initial PFC concn., and iodide concn. From 2 to 12, pH had no observable effect on PFC photoredn. kinetics, suggesting that the aquated electron was the predominant reductant with negligible contribution from the H-atom. A large no. of gaseous fluorocarbon intermediates were semi-quant. identified and detd. to account for ∼25% of the initial PFOS carbon and fluorine. Reaction mechanisms that are consistent with kinetic observations are discussed.
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    40. 40
      Sauer, M. C.; Crowell, R. A.; Shkrob, I. A. Electron photodetachment from aqueous anions. 1. Quantum yields for generation of hydrated electron by 193 and 248 nm laser photoexcitation of miscellaneous inorganic anions. J. Phys. Chem. A 2004, 108, 5490– 5502,  DOI: 10.1021/jp049722t
      40
      Electron Photodetachment from Aqueous Anions. 1. Quantum Yields for Generation of Hydrated Electron by 193 and 248 nm Laser Photoexcitation of Miscellaneous Inorganic Anions
      Sauer, Myran C., Jr.; Crowell, Robert A.; Shkrob, Ilya A.
      Journal of Physical Chemistry A (2004), 108 (25), 5490-5502CODEN: JPCAFH; ISSN:1089-5639. (American Chemical Society)
      Time-resolved transient absorption spectroscopy has been used to det. quantum yields for electron photodetachment in 193 nm and (where possible) 248 nm laser excitation of misc. aq. anions, including hexacyanoferrate(II), sulfate, halide anions (Cl-, Br-, and I-), pseudohalide anions (OH-, HS-, and CNS-), and several common inorg. anions for which no quantum yields have been reported heretofore: SO32-, NO2-, NO3-, ClO3-, and ClO4-. Molar extinction coeffs. for these anions and photoproducts of electron detachment from these anions at the excitation wavelengths were also detd. These results are discussed in the context of recent ultrafast kinetic studies and compared with the previous data obtained by product analyses. The authors suggest using electron photodetachment from the aq. halide and pseudohalide anions as actinometric stds. for time-resolved studies of aq. photosystems in the UV.
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    41. 41
      Iwata, A.; Nakashima, N.; Kusaba, M.; Izawa, Y.; Yamanaka, C. Quantum yields of hydrated electrons by UV laser irradiation. Chem. Phys. Lett. 1993, 207, 137– 142,  DOI: 10.1016/0009-2614(93)87004-m
      41
      Quantum yields of hydrated electrons by UV laser irradiation
      Iwata, Akyhiro; Nakashima, Nobuaki; Kusaba, Mitsuhiro; Izawa, Yasukazu; Yamanaka, Chiyoe
      Chemical Physics Letters (1993), 207 (2-3), 137-42CODEN: CHPLBC; ISSN:0009-2614.
      Quantum yields of hydrated electrons of Cl-, Br-, I-, SO2-4, SCN-, and OH- in aq. soln. were detd. by 193 nm laser flash photolysis. Shorter wavelength excitation showed higher quantum yields for I- and SCN- ions in 3 wavelengths of 193, 222, and 248 nm. The highest yield was 0.73 for SO2-4 at 193 nm, and the lowest one was 0.015 for SCN- at 248 nm.
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    42. 42
      Qu, Y.; Zhang, C.; Li, F.; Chen, J.; Zhou, Q. Photo-reductive defluorination of perfluorooctanoic acid in water. Water Res. 2010, 44, 2939– 2947,  DOI: 10.1016/j.watres.2010.02.019
      42
      Photo-reductive defluorination of perfluorooctanoic acid in water
      Qu, Yan; Zhang, Chaojie; Li, Fei; Chen, Jing; Zhou, Qi
      Water Research (2010), 44 (9), 2939-2947CODEN: WATRAG; ISSN:0043-1354. (Elsevier B.V.)
      Globally distributed and highly stable, perfluorooctanoic acid (PFOA) has prompted much concern regarding its accumulation in the natural environment and its threats to ecosystems. Therefore, it is desirable to develop an effective treatment against PFOA pollution. In this study, a photo-redn. method is developed and evaluated for the decompn. of perfluorooctanoic acid (PFOA) in aq. phase with potassium iodide (KI) as a mediator. The expt. was conducted under 254 nm irradn. at room temp. and pH 9 under anaerobic conditions. UV photolysis of iodide solns. led to the generation of hydrated electrons (eaq -, Eaq/e°= -2.9 V), which contributed to the defluorination of PFOA. Defluorination was confirmed by fluoride release of 98%, indicating almost complete defluorination of PFOA. Kinetic anal. indicated that the PFOA decompn. fit the first-order model with a rate const. of 7.3 × 10-3 min-1. Besides fluoride ions, addnl. intermediates identified and quantified include formic acid, acetic acid, and six short-chain perfluorocarboxylic acids (C1-C6). Furthermore, small amts. of CF3H and C2F6 were also detected as reaction products by using GC/MS. With observation of the degrdn. products and verification via an isotopic labeling method, two major defluorination pathways of PFOA are proposed: direct cleavage of C-F bonds attacked by hydrated electrons as the nucleophile; and stepwise removal of CF2 by UV irradn. and hydrolysis. This method was applied to the decompn. of PFOA in wastewater issued from a fluorochem. plant and proved to be effective.
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    43. 43
      Wong, G. T. F.; Zhang, L.-S. Chemical removal of oxygen with sulfite for the polarographic or voltammetric determination of iodate or iodide in seawater. Mar. Chem. 1992, 38, 109– 116,  DOI: 10.1016/0304-4203(92)90070-q
      43
      Chemical removal of oxygen with sulfite for the polarographic or voltammetric determination of iodate or iodide in seawater
      Wong, George T. F.; Zhang, Ling Su
      Marine Chemistry (1992), 38 (1-2), 109-16CODEN: MRCHBD; ISSN:0304-4203.
      In the direct detn. of iodate and I- in seawater by differential pulse polarog. and cathodic stripping square wave voltammetry, resp., sulfite can be used to facilitate the removal of O in the samples before they are analyzed. The reaction between sulfite and dissolved O is almost instantaneous. In comparison with the removal of O by bubbling the sample with an inert gas alone, the time needed for the anal. of a sample for iodate and I- may be reduced to ∼15 min and 5 min, resp.
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    44. 44
      Yu, K.; Li, X.; Chen, L.; Fang, J.; Chen, H.; Li, Q.; Chi, N.; Ma, J. Mechanism and efficiency of contaminant reduction by hydrated electron in the sulfite/iodide/UV process. Water Res. 2018, 129, 357– 364,  DOI: 10.1016/j.watres.2017.11.030
      44
      Mechanism and efficiency of contaminant reduction by hydrated electron in the sulfite/iodide/UV process
      Yu, Keer; Li, Xuchun; Chen, Liwei; Fang, Jingyun; Chen, Huali; Li, Qiangbiao; Chi, Nianping; Ma, Jun
      Water Research (2018), 129 (), 357-364CODEN: WATRAG; ISSN:0043-1354. (Elsevier Ltd.)
      Advanced redn. by the extremely strong reducing species, hydrated electron (e-aq), is a promising and viable approach to eliminate a wide variety of persistent and toxic contaminants. In this study, we proposed a sulfite/iodide/UV process, which offered efficient prodn. of e-aq for contaminant redn. Using monochloroacetic acid (MCAA) as a simple e-aq probe, the availability of e-aq was assessed, and the mechanism involving the roles of S(IV) and iodide in the process was elucidated. A pronounced synergistic effect of S(IV) and iodide was obsd. in MCAA reductive dechlorination. The efficiency was much more dependent on the iodide concn. due to its higher absorptivity and quantum yield of e-aq. S(IV) played a dual role by producing e-aq via photoionization of SO2-3 and by reducing the reactive iodine species formed to avoid their scavenging of e-aq. When S(IV) was available, cycling of iodide occurred, favoring the const. e-aq prodn. The formation and transformation kinetics of sulfite radical were studied to verify the roles of S(IV) and iodide in the process. A kinetic model of MCAA dechlorination was also developed to quantify the e-aq-initiated redn. efficiency, highlighting the effects of S(IV), iodide, and pH. High pH favored the redn., and the process was still effective in field surface water. This study underscores the importance of producing e-aq efficiently and of minimizing the e-aq scavenging of intermediates inherently formed and accumulated, and highlights the potential of the sulfite/iodide/UV process to efficiently eliminate recalcitrant contaminants.
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    45. 45
      Zhang, T.; Wang, J.; Yan, D.; Wang, L.; Liu, X. Efficient reduction of bromate by iodide-assisted UV/sulfite process. Catalysts 2018, 8, 652,  DOI: 10.3390/catal8120652
      There is no corresponding record for this reference.
    46. 46
      Tenorio, R.; Liu, J.; Xiao, X.; Maizel, A.; Higgins, C. P.; Schaefer, C. E.; Strathmann, T. J. Destruction of per- and polyfluoroalkyl substances (PFASs) in aqueous film-forming foam (AFFF) with UV-sulfite photoreductive treatment. Environ. Sci. Technol. 2020, 54, 6957– 6967,  DOI: 10.1021/acs.est.0c00961
      46
      Destruction of Per- and Polyfluoroalkyl Substances (PFAS) in Aqueous Film-Forming Foam (AFFF) with UV-Sulfite Photo-reductive Treatment
      Tenorio, Raul; Liu, Jinyong; Xiao, Xin; Maizel, Andrew; Higgins, Christopher P.; Schaefer, Charles E.; Strathmann, Timothy J.
      Environmental Science & Technology (2020), 54 (11), 6957-6967CODEN: ESTHAG; ISSN:0013-936X. (American Chemical Society)
      UV photochem. reactions of a sulfite (SO32-) photo-sensitizer generates strongly reducing hydrated electrons (eaq-; NHE = -2.9 V) shown to effectively degrade individual per- and polyfluoroalkyl substances (PFAS), including perfluorooctanesulfonic acid (PFOS) and perfluorooctanoic acid (PFOA). However, treatment of complex PFAS mixts. in aq. film-forming foam (AFFF) is largely unknown. UV-sulfite was applied to a dild. AFFF to characterize eaq- reactions with 15 PFAS identified by liq. chromatog./quadrupole time-of-flight mass spectrometry targeted anal. Results showed reactivity varied widely among PFAS, but reaction rates obsd. for individual PFAS in AFFF were similar to rates obsd. in single-solute expts. While some structures, including long-chain perfluoroalkyl sulfonic acids (PFSA) and perfluoroalkyl carboxylic acids (PFCA), were readily degraded, other structures, most notably short-chain PFSA and fluorotelomer sulfonic acids (FTS), were more recalcitrant. These results were consistent with those showing incomplete F- release (up to 53% of F content in AFFF) during reactions. Results also showed selected PFSA, PFCA, and FTS can form as transient intermediates or un-reactive end-products via eaq- reactions with precursor structures in AFFF. This indicated that while UV-sulfite treatment can effectively treat PFOS and PFOA to meet health advisory levels, remediation of the wider range of PFAS in AFFF is more challenging.
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    47. 47
      Kireev, S. V.; Shnyrev, S. L. Study of molecular iodine, iodate ions, iodide ions, and triiodide ions solutions absorption in the UV and visible light spectral bands. Laser Phys. 2015, 25, 075602,  DOI: 10.1088/1054-660x/25/7/075602
      47
      Study of molecular iodine, iodate ions, iodide ions, and triiodide ions solutions absorption in the UV and visible light spectral bands
      Kireev, S. V.; Shnyrev, S. L.
      Laser Physics (2015), 25 (7), 075602/1-075602/11CODEN: LAPHEJ; ISSN:1054-660X. (IOP Publishing Ltd.)
      The paper reports on exptl. studies concerning the absorption spectra of mol. iodine and its IO-3, I-, I-3 anions in the spectral band of 180-600 nm. Values of the absorption cross-sections of the above mentioned substances have been measured, and relations of absorption coeffs. to concns. have been studied. The results obtained demonstrate that the spectral band under consideration is likely to be successfully used for simultaneous real-time detection of substances contg. iodine with an absorption method using laser emission sources in the UV and visible light spectral bands.
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    48. 48
      Bolton, J. R.; Bircher, K. G.; Tumas, W.; Tolman, C. A. Figures-of-merit for the technical development and application of advanced oxidation processes. J. Adv. Oxid. Technol. 1996, 1, 13– 17,  DOI: 10.1515/jaots-1996-0104
      48
      Figures-of-merit for the technical development and application of advanced oxidation processes
      Bolton, James R.; Bircher, Keith G.; Tumas, William; Tolman, Chadwick A.
      Journal of Advanced Oxidation Technologies (1996), 1 (1), 13-17CODEN: JAOTFT; ISSN:1203-8407. (Science & Technology Integration)
      Advanced oxidn. processes (AOPs), which involve the in-situ generation of highly potent chem. oxidants such as the hydroxyl radical (·OH), have recently emerged as an important class of technologies for accelerating the oxidn. and hence destruction of a wide range of org. contaminants in polluted water and air. We propose generally applicable std. figures-of-merit for comparing these waste treatment technologies. These figures-of-merit are based on elec. energy consumption within two phenomenol. kinetic order regimes: one for high contaminant concns. (elec. energy per mass, EE/M) and one for low concns. (elec. energy per order of magnitude per m3, EE/O). We also point out that a simple understanding of the overall kinetic behavior of org. destruction in a waste stream (i.e. whether zero or first order) is necessary for describing meaningful elec. efficiencies. These std. figures-of-merit provide a direct link to the elec. efficiency (lower values mean higher efficiency) of an advanced oxidn. process, independent of the nature of the system and therefore allow for direct comparison of widely disparate AOP technologies. We have also shown that the EE/M and EE/O parameters are inversely proportional to fundamental efficiency factors, such as the lamp efficiency, the fraction of the emitted light flux that is absorbed in the water and the quantum yield of generation of active radicals.
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    49. 49
      Nzeribe, B. N.; Crimi, M.; Mededovic Thagard, S.; Holsen, T. M. Physico-chemical processes for the treatment of per- and polyfluoroalkyl substances (PFAS): A review. Crit. Rev. Environ. Sci. Technol. 2019, 49, 866– 915,  DOI: 10.1080/10643389.2018.1542916
      There is no corresponding record for this reference.
    50. 50
      Gao, J.; Liu, Z.; Bentel, M. J.; Yu, Y.; Men, Y.; Liu, J. Defluorination of omega-hydroperfluorocarboxylates (ω-HPFCAs): Distinct reactivities from perfluoro and fluorotelomeric carboxylates. Environ. Sci. Technol. 2021, 55, 14146– 14155,  DOI: 10.1021/acs.est.1c04429
      50
      Defluorination of Omega-Hydroperfluorocarboxylates (ω-HPFCAs): Distinct Reactivities from Perfluoro and Fluorotelomeric Carboxylates
      Gao, Jinyu; Liu, Zekun; Bentel, Michael J.; Yu, Yaochun; Men, Yujie; Liu, Jinyong
      Environmental Science & Technology (2021), 55 (20), 14146-14155CODEN: ESTHAG; ISSN:1520-5851. (American Chemical Society)
      Omega-hydroperfluorocarboxylates (ω-HPFCAs, HCF2-(CF2)n-1-COO-) are com. available in bulk quantities and have been applied in agrochems., fluoropolymer prodn., and semiconductor coating. In this study, we used kinetic measurements, theor. calcns., model compd. expts., and transformation product analyses to reveal novel mechanistic insights into the reductive and oxidative transformation of ω-HPFCAs. Like perfluorocarboxylates (PFCAs, CF3-(CF2)n-1-COO-), the direct linkage between HCnF2n- and -COO- enables facile degrdn. under UV/sulfite treatment. To our surprise, the presence of the H atom on the remote carbon makes ω-HPFCAs more susceptible than PFCAs to decarboxylation (i.e., yielding shorter-chain ω-HPFCAs) and less susceptible to hydrodefluorination (i.e., H/F exchange). Like fluorotelomer carboxylates (FTCAs, CnF2n+1-CH2CH2-COO-), the C-H bond in HCF2-(CF2)n-1-COO- allows hydroxyl radical oxidn. and limited defluorination. While FTCAs yielded PFCAs in all chain lengths, ω-HPFCAs only yielded -OOC-(CF2)n-1-COO- (major) and -OOC-(CF2)n-2-COO- (minor) due to the unfavorable β-fragmentation pathway that shortens the fluoroalkyl chain. We also compared two treatment sequences-UV/sulfite followed by heat/persulfate and the reverse-toward complete defluorination of ω-HPFCAs. The findings will benefit the treatment and monitoring of H-contg. per- and polyfluoroalkyl substance (PFAS) pollutants as well as the design of future fluorochems.
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    51. 51
      Buxton, G. V.; Greenstock, C. L.; Helman, W. P.; Ross, A. B. Critical review of rate constants for reactions of hydrated electrons, hydrogen atoms and hydroxyl radicals (·OH/·O–) in aqueous solution. J. Phys. Chem. Ref. Data 1988, 17, 513– 886,  DOI: 10.1063/1.555805
      51
      Critical review of rate constants for reactions of hydrated electrons, hydrogen atoms and hydroxyl radicals (·OH/·O-) in aqueous solution
      Buxton, George V.; Greenstock, Clive L.; Helman, W. Phillip; Ross, Alberta B.
      Journal of Physical and Chemical Reference Data (1988), 17 (2), 513-886CODEN: JPCRBU; ISSN:0047-2689.
      Kinetic data for the radicals H and OH in aq. soln., and the corresponding radical anions, O- and eaq-, are critically reviewed with many refs. Reactions of the radicals in aq. soln. have been studied by pulse radiolysis, flash photolysis, and other methods. Rate consts. for >3,500 reactions are tabulated, including reactions with mols., ions, and other radicals derived from inorg. and org. solutes.
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    52. 52
      Elliot, A. J. A pulse radiolysis study of the reaction of OH– with I2 and the decay of I2–. Can. J. Chem. 1992, 70, 1658– 1661,  DOI: 10.1139/v92-207
      52
      A pulse radiolysis study of the reaction of hydroxyl with iodine and the decay of I2-
      Elliot, A. John
      Canadian Journal of Chemistry (1992), 70 (6), 1658-61CODEN: CJCHAG; ISSN:0008-4042.
      The rate const. for the reaction of the OH radical with I2 was estd. as (9.5 ± 1.0) × 109 dm3 mol-1 s-1 at 20° from fitting the time dependence of the decrease in the absorption of I2 at 460 nm. Rate consts. assocd. with the decay of I2- that were required for this fitting process were also detd. They were the reaction of I2- with I2- (2k = (4.60 ± 0.05) × 109 dm3 mol-1 s-1) at an ionic strength of 1.2 × 10-2 mol dm-3; I2- with I (k = (4.6 ± 1.6) × 109 dm3 mol-1 s-1); and I with I (2k = (3.0 ± 1.0) × 1010 dm3 mol-1 s-1).
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    53. 53
      Yiin, B. S.; Margerum, D. W. Nonmetal redox kinetics: reactions of iodine and triiodide with sulfite and hydrogen sulfite and the hydrolysis of iodosulfate. Inorg. Chem. 1990, 29, 1559– 1564,  DOI: 10.1021/ic00333a023
      53
      Nonmetal redox kinetics: reactions of iodine and triiodide with sulfite and hydrogen sulfite and the hydrolysis of iodosulfate
      Yiin, Boudin S.; Margerum, Dale W.
      Inorganic Chemistry (1990), 29 (8), 1559-64CODEN: INOCAJ; ISSN:0020-1669.
      The reactions of I3- and I2 with SO3H- and SO32- at pH 4.1-6.6 were studied by the pulsed-accelerated-flow technique. Pseudo-first-order rate consts. (excess [SO32-]T and [I-] were measured in the range from 6300 to 74,000 s-1 (25.0°, μ = 0.50). A mechanism is proposed and 2nd-order rate consts. are given. The ISO3- that is formed hydrolyzes with a 1st-order rate const. of 298 s-1 at 25.0°. A temp.-dependent stopped-flow study give ΔH⧧ = 65 kJ/mol and ΔS⧧ = 21 J/mol.K for the hydrolysis reaction. The pos. ΔS⧧ value indicates a dissociative mechanism without the addn. of H2O in the transition state for ISO3- hydrolysis.
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    54. 54
      Neta, P.; Huie, R. E.; Ross, A. B. Rate constants for reactions of inorganic radicals in aqueous solution. J. Phys. Chem. Ref. Data 1988, 17, 1027– 1284,  DOI: 10.1063/1.555808
      54
      Rate constants for reactions of inorganic radicals in aqueous solution
      Neta, P.; Huie, Robert E.; Ross, Alberta B.
      Journal of Physical and Chemical Reference Data (1988), 17 (3), 1027-284CODEN: JPCRBU; ISSN:0047-2689.
      Rate consts. were compiled for reactions of various inorg. radicals produced by radiolysis or photolysis, as well as by other chem. means, in aq. solns., from many refs. Data are included for the reactions of CO2-, CO3-, O3, N3, NH2, NO2, NO3, PO32-, PO42-, SO2-, SO3-, SO4-, SO5-, SeO3-, (SCN)2-, Cl2-, Br2-, I2-, ClO2, BrO2, and misc. related radicals, with inorg. and org. compds.
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    55. 55
      Li, X.; Fang, J.; Liu, G.; Zhang, S.; Pan, B.; Ma, J. Kinetics and efficiency of the hydrated electron-induced dehalogenation by the sulfite/UV process. Water Res. 2014, 62, 220– 228,  DOI: 10.1016/j.watres.2014.05.051
      55
      Kinetics and efficiency of the hydrated electron-induced dehalogenation by the sulfite/UV process
      Li, Xuchun; Fang, Jingyun; Liu, Guifang; Zhang, Shujuan; Pan, Bingcai; Ma, Jun
      Water Research (2014), 62 (), 220-228CODEN: WATRAG; ISSN:0043-1354. (Elsevier Ltd.)
      Hydrated electron (e-aq), which is listed among the most reactive reducing species, has great potential for removal and detoxification of recalcitrant contaminants. Here we provided quant. insight into the availability and conversion of e-aq in a newly developed sulfite/UV process. Using monochloroacetic acid as a simple e-aq-probe, the e-aq-induced dehalogenation kinetics in synthetic and surface water was well predicted by the developed models. The models interpreted the complex roles of pH and S(IV), and also revealed the pos. effects of UV intensity and temp. quant. Impacts of humic acid, ferrous ion, carbonate/bicarbonate, and surface water matrix were also examd. Despite the retardation of dehalogenation by electron scavengers, the process was effective even in surface water. Efficiency of the process was discussed, and the optimization approaches were proposed. This study is believed to better understand the e-aq-induced dehalogenation by the sulfite/UV process in a quant. manner, which is very important for its potential application in water treatment.
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    56. 56
      Bray, W. C.; Liebhafsky, H. A. Reactions involving hydrogen peroxide, iodine and iodate ion. I. Introduction. J. Am. Chem. Soc. 1931, 53, 38– 44,  DOI: 10.1021/ja01352a006
      56
      Reactions involving hydrogen peroxide, iodine and iodate ion. I. Introduction
      Bray, Wm. C.; Liebhafsky, Herman A.
      Journal of the American Chemical Society (1931), 53 (), 38-44CODEN: JACSAT; ISSN:0002-7863.
      A crit. review and discussion of various reactions of H2O2 in acid solns. contg. I and iodate or iodide are based on the following table:
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    57. 57
      Gregor, H. P.; Belle, J.; Marcus, R. A. Studies on ion-exchange resins. XIII. Selectivity coefficients of quaternary base anion-exchange resins toward univalent anions. J. Am. Chem. Soc. 1955, 77, 2713– 2719,  DOI: 10.1021/ja01615a011
      57
      Ion-exchange resins. XIII. Selectivity coefficients of quaternary base anion-exchange resins toward univalent anions
      Gregor, Harry P.; Belle, Jack; Marcus, R. A.
      Journal of the American Chemical Society (1955), 77 (), 2713-19CODEN: JACSAT; ISSN:0002-7863.
      cf. C.A. 48, 7389f; 49, 3614h. Selectivity coeffs., Kd, of a quaternary ammonium anion-exchange resin (Dowex 2) toward a no. of univalent anions were measured by column and batch (shaking) procedures. The concns. of the solns. were 0.01-0.1 molal, temps. were from 5 to 25°, and various samples of the Dowex 2 had DVB contents of 1, 2, 4, 8, and 16%. The effect of temp. on the distribution coeff. was small; the concns. of the solns., when dil., had a negligible effect on the selectivity. The anions investigated could be divided into a Group A: halides, CH3COO, IO3, NO3, and a Group B: SCN, ClO4, CHCl2COO, CCl3COO, CF3COO, toluenesulfonate, naphthalenesulfonate. In systems involving various pairs of ions wholly from Group A or of pairs of ions wholly from Group B, the Kd varied little with compn., but Kd changed markedly when the systems were made up of anions of Group A with one from Group B. These data were interpreted in terms of 2 postulated types of specific interactions (ion-pair formation) of these ions with those of the resin matrix. The ion-pairs of Group A were assumed to be randomly distributed in the resin phase, whereas those of Group B were assumed to occur in the form of patches or clusters.
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    58. 58
      Hildebrand, J. H.; Benesi, H. A.; Mower, L. M. Solubility of iodine in ethyl alcohol, ethyl ether, mesitylene, p-xylene, 2,2-dimethylbutane, cyclohexane and perfluoro-n-heptane. J. Am. Chem. Soc. 1950, 72, 1017– 1020,  DOI: 10.1021/ja01158a096
      58
      Solubility of iodine in ethyl alcohol, ethyl ether, mesitylene, p-xylene, 2,2-dimethylbutane, cyclohexane, and perfluoroheptane
      Hildebrand, J. H.; Benesi, H. A.; Mower, L. M.
      Journal of the American Chemical Society (1950), 72 (), 1017-20CODEN: JACSAT; ISSN:0002-7863.
      The soly. of I in CS2, 2,2-dimethylbutane, cyclohexane, EtOH, Et2O, p-xylene, mesitylene, and C7F16 at 0.0° is 2.440, 0.164, -, 3.51, 6.54, -, 6.89, and 0.0038 mole %, resp.; at 25.0°, 5.58, 0.469, 0.918, 4.71, 8.96, 7.66, 10.72, and 0.0182 mole %, resp.; and at 35°, 7.64, 0.684, 1.329, 5.59, 10.43. 9.54, - and 0.0286 mole %, resp. The solvation in the case of mesitylene and p-xylene increases the I soly. over the value for regular solns., the increase being greatest for mesitylene. The enhancement of I solubilities in these solvents is in good agreement with equil. data obtained from earlier spectroscopic measurements (C.A. 43, 7824h) and therefore provides further evidence for the existence of an acid-base interaction between aromatic hydrocarbons and I. The I solubilities in unsolvated solns. are in accord with the behavior predicted from the internal pressures of the pure solvents.
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    • Details of PFAS chemicals; quantitation of PFAS parent compounds, TPs, and anions; extended discussions on kinetic data fitting and photoreactor configurations; and defluorination profiles in the two photoreactor configurations (PDF)


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