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Ice Nucleation Activity of Graphene and Graphene Oxides

Cite this: J. Phys. Chem. C 2018, 122, 15, 8182–8190
Publication Date (Web):March 1, 2018
https://doi.org/10.1021/acs.jpcc.7b10675

Copyright © 2018 American Chemical Society. This publication is licensed under CC-BY.

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Abstract

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Aerosols can act as cloud condensation nuclei and/or ice-nucleating particles (INPs), influencing cloud properties. In particular, INPs show a variety of different and complex mechanisms when interacting with water during the freezing process. To gain a fundamental understanding of the heterogeneous freezing mechanisms, studies with proxies for atmospheric INPs must be performed. Graphene and its derivatives offer suitable model systems for soot particles, which are ubiquitous aerosols in the atmosphere. In this work, we present an investigation of the ice nucleation activity (INA) of different types of graphene and graphene oxides. Immersion droplet freezing experiments as well as additional analytical analyses, such as X-ray photoelectron spectroscopy, Raman spectroscopy, and transmission electron microscopy, were performed. We show within a group of samples that a highly ordered graphene lattice (Raman G band intensity >50%) can support ice nucleation more effectively than a lowly ordered graphene lattice (Raman G band intensity <20%). Ammonia-functionalized graphene revealed the highest INA of all samples. Atmospheric ammonia is known to play a primary role in the formation of secondary particulate matter, forming ammonium-containing aerosols. The influence of functionalization on interactions between the particle interface and water molecules, as well as on hydrophobicity and agglomeration processes, is discussed.

Introduction

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At temperatures below −35 °C, ice forms via the homogeneous nucleation of supercooled droplets or heterogeneous nucleation on ice-nucleating particles (INPs). (1−3) At temperatures above −35 °C, heterogeneous nucleation is considered to be the dominant mechanism. (3,4) Therefore, INPs play a major role in the ice forming process in clouds. The composition and origin of INPs have been studied intensively over the past few decades, as summarized, for example, by Murray et al. (5) However, the microscopic and molecular mechanisms of heterogeneous ice nucleation are complex and remain poorly understood. Necessary attributes, such as the ice-like structure or hydrophobicity of the INP, can rarely be applied. (3) Factors controlling heterogeneous processes have been investigated intensively, but the knowledge remains fragmentary. (5) To answer the major question of ice nucleation—what makes an effective ice-nucleating site?—investigations need to focus on simple INP proxies. Consequently, more laboratory and atmospheric data are required. (6)
In this work, we focus on surrogates of soot particles. A series of studies demonstrated that black carbon as well as organic soot components forms a large fraction of urban aerosols. (7−9) The ice nucleation activity (INA) of soot has been well-investigated, for example, by DeMott (10) and Dymarska et al. (11) Nevertheless, the complexity of the atmospheric soot makes forecasts of their ice-nucleating behavior rather difficult. Several laboratory and field studies showed that an increase in the INA of aged soot results from an increase in the hydrophilicity of the surface upon oxidation. (12−16) However, oxidation also impacts the nanostructure of the soot, making it difficult to assess the separate effects of soot nanostructure and hydrophilicity via experiments. Therefore, graphene, a simple proxy substance with chemical and structural similarities to soot, (17,18) was investigated to confirm or correct the established rules regarding the necessary ice nucleation characteristics. Graphene is a single two-dimensional layer of carbon atoms bound in a hexagonal lattice structure. (17) It was first isolated and identified in 1962 by Böhm. (19) Since then, graphene has been the focus of extensive studies, primarily because of its exceptional electrical, thermal, and mechanical properties. (20)
Lupi and Molinero (21) used molecular dynamics simulations to investigate the effect of changes in the hydrophilicity of model graphitic surfaces on the freezing temperature of ice. Their results indicate that the ordering of liquid water in contact with the surface plays an important role in the heterogeneous ice nucleation mechanism and that the hydrophilicity of the surface is not generally a good predictor of the INA. These ordered water molecule domains of bilayer hexagons are necessary for the INA of graphene but have not been observed on hydrophobic or hydrophilic atomically rough surfaces. They suggested that knowledge of the actual nanostructure and spatial distribution of chemical groups in soot and other atmospheric carbon particles is needed for an accurate prediction of the INA of these aerosols. A molecular dynamics study by Bi et al. (22) revealed that a crystalline graphitic lattice with an appropriate hydrophilicity may indeed template ice and thus significantly enhance its INA. Their calculations demonstrated that the templating effect is found to transit from within the first contact layer of water to the second as the hydrophilicity increases, yielding an oscillating distinction in the INA of crystalline and amorphous graphitic surfaces. Furthermore, it was evident that crystalline graphene becomes up to 105 times more efficient within certain hydrophilicity ranges, suggesting that the crystallinity is also a key factor for ice nucleation under such hydrophilicity. The experimental investigation of Zheng et al. (23) showed that a sprinkle of graphene oxide nanoflakes is effective for condensing water nanodroplets and seeding ice epitaxy on graphite under ambient conditions. They discovered that ice nucleation and growth can be influenced by modifying the functional groups of graphene oxide nanoflakes and by intermolecular hydrogen bonding between nanoflakes. Carboxylate groups introduced by base treatment play a key role in the INA of graphene oxide nanoflakes. So-called “charge-assisted hydrogen bonding” (24) allows interaction with water molecules, thus increasing the INA. Reduction via acid or ammonium treatment decreases the INA significantly. Furthermore, by arranging graphene oxide nanoflakes in one dimension, an ice-like structure can be induced, leading to an increase in the INA. A phenyl ring structure, however, reduces the number of possible hydrogen-bonding carbonyl sites for ice nucleation and decreases the INA.
Whale et al. (25) investigated different kinds of carbon nanomaterials in laboratory experiments using an immersion freezing technique. Their results agreed with the calculations done by Lupi and Molinero (21) and Lupi et al. (26) and showed that materials with a lower oxidation state nucleate ice more efficiently than materials with a higher oxidation state. Any oxidation, roughness or curvature was found to decrease the observed nucleation temperature. The result that oxidized surfaces nucleate ice less well than atomically flat surfaces is somewhat in contradiction with the commonly stated “chemical bonding” requirement for ice nucleation. (3) Oxides or other polar groups on the surface of INPs are meant to offer so-called functional sites that are able to interact with water molecules and nucleate ice.
Biggs et al. (27) modified graphene oxides by means of thiol–epoxy chemistry, resulting in materials with increased INA. They revealed that hydrophobic chains increased the heterogeneous nucleation temperature from −22.5 to −12.5 °C. Hydrophilic surface modifications did not promote the activity but also did not reduce the underlying INA of the graphene oxide. They suggested that due to the functionalization and increase in hydrophobicity, an increased degree of aggregation occurred, with larger aggregates potentially leading to more nucleation. Ammonia is highly relevant in the atmosphere, as it has been shown to play a primary role in the formation of secondary particulate matter, forming ammonium-containing aerosols. (28) Ammonium-containing aerosols constitute the major fraction of PM2.5 aerosols in the atmosphere. (28) Anthropogenic ammonia originates, for example, from soil because of agriculture activities and from industrial and traffic emissions. (29,30) Therefore, ammonia-functionalized graphene should be investigated.
Because of the differences in approaches concerning the required features of an INP, investigations of simple and closely related INPs are important to gain more information on the characteristics of a functional site. Therefore, graphene was chosen to be a good proxy substance to fundamentally understand heterogeneous ice nucleation. The goal of our study was to investigate the immersion-mode ice nucleation characteristics of different kinds of graphene and graphene modifications. Moreover, the graphene samples were analyzed regarding their chemistry and structure by means of X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, and transmission electron microscopy. Combining these data, we propose possible explanations as to why some graphene samples are good INPs while others are not.

Methods

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The INA was determined by an oil-immersion freezing technique, which was used in recent publications, for example, by Hauptmann et al., (31) Pummer et al., (32) and Zolles et al. (33) Supplementary analytical techniques were applied to characterize the chemical properties, surface and bulk properties, and morphology of the INPs.

Cryomicroscopy

The measurement setup consisted of a custom-built freezing cell that was placed directly underneath a light microscope. This experimental setup has been used in previous studies, in which a detailed description can be found. (32,33) Here, only a short description of the technique is given. The experimental setup consisted of a light microscope to observe the freezing experiment, a freezing cell to cool the sample, and a computer to control the cell temperature and cooling rate. The main part of the custom-built freezing cell is a thermoelectric cooler (TEC, Peltier element Quick-Cool QC-31-1.4-3.7). The TEC enables cooling rates between 0.1 and 10 °C/min down to a temperature of −40 °C. Two gas connectors on the shell of the freezing cell allow flushing with dry nitrogen. This is done before every experiment to remove humidity and to establish a neutral atmosphere. The freezing process is observed via a glass window on top of the freezing cell using the light microscope. The INA of the graphene samples was determined in the immersion freezing mode using a water–oil emulsion technique. A stable suspension of the INPs in ultrapure water was achieved by sonication for 5 min with an operating frequency of 40 kHz. Graphene is considered to disperse poorly in water. (34,35) Nevertheless, the oxidation of graphene together with the use of sonication allows graphene and graphene oxides to be dispersed in a larger number of solvents, including water. (34,35) The samples used in this work revealed a sufficient degree of oxidation to achieve stable suspensions. Images of the selected aqueous graphene and graphene oxide suspensions immediately after sonication and after settling for 30 min are provided in the Supporting Information (see Figure S1). To avoid any subsequent phase separation, further preparation steps were carried out immediately after sonication. Graphene samples from Sigma-Aldrich were purchased directly as an aqueous suspension. The suspensions were emulsified into an oil matrix (80 wt % paraffin, 20 wt % lanolin), producing droplets in the micrometer range with a diameter of 20–80 μm. Only droplets with diameters between 35 and 45 μm were used for evaluation. The water–oil emulsion was put on a glass slide and placed on the TEC. The migration of individual particles into the oil phase cannot be excluded. To minimize migration, the time between emulsification and the start of the cooling process was intentionally kept short. A refreezing experiment was performed to demonstrate that no migration into the oil phase occurs during the freezing experiment and is provided in the Supporting Information (see Figure S2).
The TEC was cooled at a constant cooling rate of 2 °C/min. The temperature accuracy was ±0.5 °C. The freezing process was recorded with a microscope camera and then analyzed. The frozen droplets can be easily distinguished from the liquid droplets, as they appear darker because of their different light-scattering properties. The so-called ice nucleation active surface site density ns (36−39) was used to describe ice nucleation because the total surface area of INPs per droplet is important to their activity, as predicted by the classical nucleation theory and confirmed by Edwards et al. (40)N0 is the total number of droplets in the experiment, NF is the number of frozen droplets at temperature T, and s is the particle surface per droplet. The fraction of frozen droplets f(T) is given by
(1)
The surface area was determined via nitrogen adsorption and assumed to be equal to the available surface area in suspension.
By increasing the size of droplets from cloud droplet size (diameters of approximately 10 μm) to approximately 40 μm, the surface area per droplet for a constant mass fraction of INPs in water was increased. According to eq 1, this allows the quantification of ns to smaller values and the determination of nucleation efficiencies over a wider range of temperatures than that is possible by using cloud-sized droplets. (41)

X-ray Photoelectron Spectroscopy

XPS was carried out using the facilities of the Analytical Instrumentation Center AIC at the TU Wien. Measurements were performed with a SPECS XPS spectrometer equipped with an Al Kα X-ray source (μFocus 350) and a hemispherical WAL-150 analyzer. The excitation energy was set to 1486.6 eV, the pass energy was 30 eV, and the resolution was 50 meV. The lower detection limit of quantification was 0.1 at. % with an accuracy of 10–20%, depending on the element. For preparation, the samples were drop-coated on a silicon single crystal.

Raman Spectroscopy

The Raman microscope system (Jobin Yvon, LabRAM HR) consisted of a light microscope (Olympus BX) coupled to a Raman spectrometer. A 20-fold objective and a grating with 300 g/mm were used. Furthermore, 60 scans with an exposure of 5 s each were collected to obtain a sufficient signal-to-noise ratio using a laser with a wavelength of 633 nm. The interpretation and evaluation of the Raman spectra were performed according to Sadezky et al. (42) By applying and fitting potential vibrational bands (see Table 1) to the measured Raman spectra, qualitative and quantitative descriptions of the graphene lattice and its disorder can be made. The appearance of individual vibrational bands provides a qualitative description, while the proportional integrated intensities provide information on the contribution of each vibration. The band intensities are expressed as a fraction of the total intensity.
Table 1. First-Order Raman Bands and Vibrational Modes of Soot and Graphite According to Sadezky et al. (42) for Interpretation of the Obtained Raman Spectra (vs = Very Strong, s = Strong, m = Medium, and w = Weak)a
  Raman shift [cm–1]  
band soot disordered graphitec vibrational modeb
G ∼1580, s ∼1580, s ideal graphitic lattice (E2g symmetry)
D1 ∼1350, vs ∼1350, m disordered graphitic lattice (graphene layer edges, A1g symmetry)
D2 ∼1620, s ∼1620, w disordered graphitic lattice (surface graphene layers, E2g symmetry)
D3 ∼1500, m   amorphous carbon (Gaussian line shaped)
D4 ∼1200, w   disordered graphitic lattice (A1g symmetry), polyenes, and ionic impurities
a

Minor changes in the Raman shifts may occur because of the different measurement parameters.

b

Lorentzian line shaped unless otherwise mentioned.

c

Polycrystalline graphite (<100 nm) and boron-doped highly oriented polycrystalline graphite (HOPG).

Transmission Electron Microscopy

TEM measurements were performed on FEI Tecnai F20 with an acceleration voltage of 200 kV. The samples were prepared by adding dropwise an aqueous or ethanolic solution on Lacey(R)-coated copper grids.

Nitrogen Adsorption

The surface areas of the samples were measured using a commercial liquid nitrogen adsorption system (ASAP 2020, Micromeritics). Data evaluation was based on the model by Brunauer, Emmett, and Teller (BET). (43)

Description of Materials

We investigated a variety of functionalized and nonfunctionalized graphene and graphene oxide materials with different chemical and structural characteristics to evaluate the dependence of the INA on the surface chemistry, micromorphology, and nanomorphology. Four graphene oxides (GO) were chosen for investigation: (i) GO synthesized by our group (GO-DE), (ii) GO purchased from Sigma-Aldrich (GO-SA), (iii) ammonia-functionalized GO (GO-NH2), and (iv) nanosized colloidal GO (GO-nano). Moreover, three graphene samples were analyzed: (i) nonfunctionalized graphene (G-non) and (ii) and (iii) covalently functionalized graphene G-NPr3+X– (X = I and OH). Table 2 summarizes the material characteristics, including the source of synthesis and the specific surface area according to BET. The representative chemical structures are given in Figure 1. The synthesis and further characterization are provided in the Supporting Information (see Scheme S1 and S2, Figures S3–S16).

Figure 1

Figure 1. Representative chemical structures of the samples investigated: (a) nonfunctionalized graphene G-non, (44) (b) covalently functionalized graphene G-NPr3+X– (X = I and OH), (c) graphene oxide nanocolloids GO-nano, (d) graphene oxide GO-DE and GO-SA, (45) and (e) ammonia-functionalized graphene oxide GO-ammo. According to the provided datasheet of the purchased material from Sigma-Aldrich Chemistry.

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Table 2. List of Samples Investigated, Including the Sources of Each Sample, BET-Determined Surface Areas and a Short Description of the Samples, Including TEM-Determined Particle Thickness and Shape
material surface areas [m2/g] description
Graphene Oxides
GO-DEa 112 large single-layer graphene oxide sheets (>1 μm)
GO-SAb <10 large 2–7 multi-layer graphene oxide sheets (>1 μm)
GO-NH2b <10 large 2–7 multi-layer graphene oxide sheets (>1 μm), ammonia functionalized
GO-nanob 176 graphene oxide nanocolloids with varying particle size/shape up to 200 nm and thickness of >3 nm
Graphene
G-nona <10 nonfunctionalized graphene flakes with a diameter of 400 nm and up to 7 layers; precursor for G-NPr3+I/OH–
G-NPr3+I–a <10 covalently functionalized graphene with I– as the counter ion; same form and shape as that of G-non
G-NPr3+OH–a <10 covalently functionalized graphene with OH– as the counter ion; same form and shape as that of G-non
a

Synthesized by our workgroup.

b

Acquired from Sigma-Aldrich Chemistry.

Results

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The INA of the entire set of samples is shown in Figure 2. For clarity, the samples were divided into two groups according to their chemical characteristics: (i) graphene, including G-non, G-NPr3+I–, and G-NPr3+OH–, and (ii) graphene oxides, including GO-DE, GO-SA, GO-nano, and GO-NH2 (see Table 2).

Figure 2

Figure 2. (a) Ratio of frozen droplets fice and (b) the ice nucleation active surface site density ns at a given temperature for all investigated samples. The ns value, the freezing temperature range, and the ns trend provide key information on the characteristics of the ice-nucleation-active samples of graphene or graphene oxides. Some droplets nucleate at about −36 °C, meaning that they do not contain INPs. Experimental uncertainty in the ns value was calculated by changes in the weight and droplet size.

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Graphene

Covalently functionalized graphene (G-NPr3+I– and G-NPr3+OH–) show a similar INA with slightly increased ns values of G-NPr3+OH– between −30 and −36.5 °C compared to G-NPr3+I–. In contrast, nonfunctionalized graphene (G-non) shows an increased INA once the temperature is below −28 °C compared to the functionalized samples. XPS measurements were performed to determine the elemental composition and the sp2-hybridized carbon (C-sp2) proportion. The C-sp2 proportions are representative for the graphitic carbon ratio (see Table 3). The detailed list of XPS-determined carbon components is given in the Supporting Information (see Table S1). The composition of the three samples is similar and consists of approximately 91–92 at. % carbon and 4–9 at. % oxygen. G-NPr3+I– and G-NPr3+OH– show a nitrogen proportion of 3–4 at. % as well as 1 at. % iodine for G-NPr3+I– originating from the functionalization (see Figure 1). The C-sp2 proportions are between 72 at. % for G-NPr3+OH– and 91 at. % for G-NPr3+I–.
Table 3. Elemental Composition and sp2-Hybridized Carbon Proportion of All Investigated Graphene Samples Determined via XPS
  element [at. %]  
sample C O N I C-sp2 [at. %]
G-non 91 9     86
G-NPr3+I– 92 4 3 1 91
G-NPr3+OH– 92 4 4   72
Raman spectroscopy was performed and analyzed according to Sadezky et al. (42) to distinguish the differences in the microstructure, lattice disorder, and short-range order. The Raman spectra (see Table 4 and Figure 3) reveal that nonfunctionalized graphene (G-non) has fewer structural defects, shown by the lower intensity of the disordered band D1 (layer edge disorder) of 27% and the higher intensity of the ideal graphite band G of 69% compared to those of covalently functionalized graphene. Covalently functionalized graphene exhibits an integrated intensity of D1 of up to 40% for G-NPr3+OH– and 44% for G-NPr3+I–. The intensity of D2 is shown to be similar, within a ±1% range for all three samples.

Figure 3

Figure 3. Raman spectra of (a) all investigated graphene samples and (b) nonfunctionalized graphene (G-non); first-order curve fitted with band combination according to Table 1 (λ0 = 633 nm).

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Table 4. Proportional Intensities of Fitted First-Order Raman Impulses (G, D1, and D2) According to Sadezky et al. (42) and Ratios of the Raman Band Intensity of the Disordered to the Ideal Graphitic Lattice (D/G) of All Investigated Graphene Samples
  proportional intensity of fitted bands [%]
sample G D1 D2 D/G
G-non 69 27 4 0.45
G-NPr3+I– 51 44 4 0.94
G-NPr3+OH– 57 40 3 0.75
Additionally, TEM measurements were performed to determine the morphology of the particles. The images reveal flakes with diameters of up to 400 nm and with up to 7 layers (see Figure 4) for all three graphene samples. Individual sheets of G-non, however, show additional accumulation, forming larger “fluffy” aggregates.

Figure 4

Figure 4. TEM images of graphene samples investigated: (a) nonfunctionalized graphene (G-non) indicates flakes with diameters of up to 400 nm and with up to 7 layers (46) and (b) covalently functionalized graphene (G-NPr3+I– and G-NPr3+OH–) shows the same layer size and thickness as its nonfunctionalized precursor G-non but also shows individual sheets accumulating into larger “fluffy” aggregates.

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Graphene Oxides

Graphene oxides show a broader variety of INA than graphene (see Figure 2). The ns values of the chemically most similar graphene oxide samples GO-DE and GO-SA show a deviation of 2 orders of magnitude but an increase at a similar rate over the entire temperature window. The ns value of GO-SA increases from 3 × 103 cm–2 at −25 °C to 105 cm–2 at −35 °C and that of GO-DE increases from 20 cm–2 at −25 °C to 7 × 102 cm–2 at −35 °C. GO-nano, on the other hand, initiates the ice nucleation process at a range similar to GO-DE at −27.5 °C, with a ns value of 130 cm–2. The ns value, however, rises more steeply until it reaches the same value as GO-SA of 3 × 104 cm–2 at −32.5 °C. The functionalized graphene oxide sample (GO-NH2) shows the highest INA of all samples investigated over the entire freezing process, revealing ns values between 104 cm–2 at −25 °C and 3 × 105 cm–2 at −35 °C.
XPS measurements show a similar composition among all graphene oxide samples, that is, of approximately 67–73 at. % carbon and 23–33 at. % oxygen (see Table 5). GO-nano is composed of an increased amount of oxygen (33 at. %) and a consequently decreased proportion of carbon (67%). GO-NH2 additionally consists of approximately 3 at. % nitrogen due to the ammonia functionalization. The proportion of sp2-hybridized carbon lies between 19 at. % for GO-nano and 45 at. % for GO-DE.
Table 5. Elemental Composition and Proportion of sp2-Hybridized Carbon (C-Sp2) of All Investigated Graphene Oxide Samples Determined via XPS
  element [at. %]  
sample C O N C-sp2 [at. %]
GO-SA 71 28 <1 29
GO-DE 72 27 <1 45
GO-nano 67 33 <1 19
GO-NH2 73 23 3 42
Furthermore, Raman spectroscopy reveals distinctions in lattice orders (see Table 6 and Figure 5). In contrast to graphene, the graphene oxide samples show a more complex composition of lattice disorders. The D/G ratio is a suitable indicator of the degree of disorder, which increases from GO-SA (4.82) to GO-NH2 (9.0). The D value summarizes the integral intensities of all D-bands (D1–D4): edge (D1) and surface (D2) disorders, amorphous graphene oxide features (D3), and ionic impurities/polyene disorders (D4). GO-DE exhibits an increased ratio of integrated intensities of D3 (7%) and D4 (4%) compared to the chemically most similar sample, GO-SA. The Raman spectrum of GO-nano reveals a disordered lattice with an integrated intensity of amorphous disorder of 11%, making this sample the most amorphous of all samples. Nevertheless, GO-NH2 exhibits the more intense disorder, which is evident in the lowest integrated intensity of the ideal lattice of 10%.

Figure 5

Figure 5. Raman spectra of (a) all investigated graphene oxide samples and (b) GO-NH2; first-order curve fitted with band combination according to Table 1 (λ0 = 633 nm).

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Table 6. Proportional Intensities of Fitted First-Order Raman Impulses (G, D1, and D2) According to Sadezky et al. (42) and Ratios of the Raman Band Intensity of the Disordered to the Ideal Graphitic Lattice (D/G) of All Investigated Graphene Oxide Samples
  proportional intensity of fitted bands [%]
sample G D1 D2 D3 D4 D/G
GO-SA 17 68 7 5 2 4.82
GO-DE 14 69 7 7 4 6.21
GO-nano 14 64 6 11 5 6.14
GO-NH2 10 70 8 8 4 9.0
TEM analysis of GO-SA, GO-DE, and GO-NH2 reveal similar large flakes of several μm in diameter and a thickness of 2–7 layers. GO-nano, on the other hand, consists of particles of varying shapes and sizes of up to 200 nm and thicknesses of at least 3 nm (see Figure 6).

Figure 6

Figure 6. TEM images of the samples investigated: (a) nonfunctionalized (GO-SA and GO-DE) and ammonia-functionalized graphene oxides (GO-NH2) reveal large flakes of approximately 5 nm thickness and several micrometers in diameter, and the thickness of the sheets and number of signals in the corresponding electron diffraction pattern indicate multi-layer graphene composed of 2–7 layers, while (b) GO-nano consists of particles of varying shapes with sizes of up to 200 nm and thickness of at least 3 nm.

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Discussion

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Graphene

In Figure 2, the functionalized graphene samples show a similar INA, with slightly increased ns values for G-NPr3+OH– between −30 and −36.5 °C. In contrast, nonfunctionalized graphene (G-non) shows an increased INA above −28 °C compared to the functionalized samples. TEM analyses indicate that the flake and layer size of functionalized graphene stay nearly the same as that of nonfunctionalized graphene. Differences in composition revealed by XPS might influence the INA because of the introduction of additional functional sites that are able to interact with water molecules and trigger ice formation. This would be consistent with the classical chemical-bonding requirement stated by Pruppacher and Klett. (3) The Raman data revealed that covalently functionalized graphene (G-NPr3+I– and G-NPr3+OH–) exhibits an increased integrated intensity of lattice disorders. With a decrease in the D/G ratio of functionalized graphene, the INA decreases at a similar rate (see Table 4). The functionalization process seems to have a major influence on the INA. The ordering process of water molecules at the water–graphene interface supports heterogeneous ice nucleation and depends on the lattice features. Disorientations of the lattice disturb the interaction with liquid water and therefore lower the INA of graphene. Thus, the graphene lattice is a significant parameter influencing the INA of graphene and is also responsible for the INA of soot particles. This is consistent with calculations of Lupi et al., (26) Lupi and Molinero, (21) and Bi et al. (22) and the laboratory work of Whale et al., (25) which revealed that the ordering of liquid water on an ideal graphitic lattice plays an important role in the heterogeneous ice nucleation mechanism and any oxidation, roughness, or curvature was found to decrease the observed nucleation temperature. Nevertheless, accumulations of G-NPr3+I– and G-NPr3+OH– flakes into larger aggregates, as demonstrated in Figure 4, may reduce the INA by reducing the available active surface area, which needs to be considered. According to the data obtained in this study, it can be stated that the lattice conditions have an impact on the INA of graphene, yet the influence of agglomeration and functionalization cannot be excluded. However, more graphene species need to be investigated to state a significant trend and distinguish the relevance of each influence.

Graphene Oxides

The INA of graphene oxide appears to be more complex. In contrast to graphene, the graphene oxide samples not only show significant differences in composition but also experience additional lattice disorder. Because of oxidation, the C-sp2 proportions of the graphene oxides were cut by one-half compared to the graphene samples because of an increased amount of carbon-containing contaminants (see Tables 3 and 5). The ns values of the chemically most similar graphene oxide samples, GO-DE and GO-SA, show a deviation of 2 orders of magnitude but increase at a similar rate over the entire temperature window. Furthermore, a consistent chemical composition and particle form was shown for both samples. In contrast, the lattice of GO-DE features an increased portion of structural disorder (D/G of 6.21) compared to GO-SA (D/G of 4.82). Because of the similarity in composition and particle shape, the significant differences in lattice order of GO-DE and GO-SA may account for the activity difference observed for the graphene samples. However, the observed dependence of INA on the lattice order cannot be applied to all graphene oxide samples investigated. In particular, GO-nano initiates ice nucleation in the same range as GO-DE, but nucleation increases substantially more steeply until it reaches the same value as GO-SA at −32.5 °C (see Figure 2). The degree of graphitization, however, is in the same range as that of GO-DE and GO-SA, with an amorphous proportion of 11% being the highest of all samples (see Table 6). GO-nano shows an increased amount of oxygen (33 at. %) and a corresponding decreased proportion of carbon (see Table 5). Nevertheless, GO-nano consists of significantly smaller particles of varying shapes and sizes of up to 200 nm and thicknesses of at least 3 nm (see Figure 6). On the basis of the data, three features may account for the increased INA of GO-nano: (i) the particle shape of GO-nano may cause an increase in the INA because of the beneficial arrangement of functional sites on the surface, (ii) additional oxygen groups act as functional sites and improve the interaction of the graphene oxide interface with water molecules because of a possible increase in hydrogen bonds, and (iii) the increased proportion of oxygen increases the hydrophilicity of graphene, reduces agglomeration, and hence increases the surface area. However, the influence of hydrophilicity and the resulting agglomeration is not clear. Biggs et al. (27) reported an increase in the INA due to a decrease in hydrophilicity. The resulting agglomeration may have led to a favorable positioning of the functional site and therefore to an increase in the INA, even though a decrease in the surface area occurs.
XPS measurements of GO-NH2 revealed a composition of 73 at. % carbon, 23 at. % oxygen, and 3 at. % nitrogen due to functionalization. GO-NH2 exhibits the highest integrated intensity of disorder (G <10%) and the highest INA of all samples investigated. Amines are known to be more hydrophilic than comparable organic hydrocarbons because of their polarity and basicity. (47) They therefore interact more easily with other polar groups, such as water molecules, via hydrogen bonds and may act as functional sites, increasing the INA. However, very few proteins show INA, despite containing lysine, an amino-group-containing amino acid, and instead are known to act as antifreeze. (48,49) The influence of increased hydrophilicity and therefore reduced agglomeration of G-NH2 flakes in aqueous suspension may lead to an increased INA and cannot be excluded. Exfoliation can lead to an increase in the surface area and hence may increase the INA.

Summary

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In this work, we investigated the INA of different types of graphene and graphene oxides. Immersion drop freezing experiments as well as additional analytical analyses such as X-ray photoelectron spectroscopy, Raman spectroscopy, and transmission electron microscopy were performed to gain insight into the surface chemistry, micromorphology, and nanomorphology of the INPs. The investigation of graphene and graphene oxides show that the lattice order can have a major impact on the INA. The introduction of different kinds of disorders (layer edges, amorphousness, impurities, etc.) can influence the ability to perform heterogeneous ice nucleation. The ordering of water molecules at the interface to perform heterogeneous ice nucleation seems to depend on the graphitic lattice. Disorders in the lattice disturb the interactions with liquid water and therefore lower the INA of graphene. However, the observed dependence of the INA on the lattice order cannot be applied to all investigated graphene oxide samples. In particular, GO-NH2 exhibits the highest proportion of disorder (G <10%) and revealed the highest INA of all samples investigated. Functionalization with amines influences the INA by increasing the number of functional sites and/or by increasing the hydrophilicity. In general, two other INP characteristics in addition to the lattice order were shown to influence the INA of graphene and graphene oxides: (i) the particle size, in particular that within the nanometer range, may cause an increase in the INA due to the beneficial arrangement of functional sites on the surface and (ii) the degree of oxidation, which influences the hydrophilicity, reduces agglomeration, and hence increases the surface area, as well as generates functional sites.
On the basis of this work, the impact of the lattice order was demonstrated. Additionally, differences in structure, size, and functionalization between the investigated samples are shown. More species with closely controlled differences need to be investigated to state a firm experimental conclusion about the effect of each feature on the INA. Therefore, declarations of the most decisive ice nucleation feature cannot be made. A variety of features relevant to ice nucleation were shown to be essential when describing the ice-nucleating behavior of graphene and graphene oxides.

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The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.jpcc.7b10675.

  • Synthesis and characterization of functionalized graphene samples (G-NPr3+X–); visual comparison of graphene and graphene oxide suspensions after sonication and after settling for 30 min; refreezing experiments of G-non; and XPS-determined C 1s components of all samples (PDF)

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Acknowledgments

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We thank the Austrian Science Fund (FWF) for the financial support (project number P26040). XPS measurements were carried out using facilities of the “Analytical Instrumentation Center”, TU Wien, Austria. TEM measurements were performed at the University Service Centre for Transmission Electron Microscopy (USTEM, TU Wien).

References

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    Angewandte Chemie, International Edition (2002), 41 (1), 48-76CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH)
    A review. The hydrogen bond is the most important of all directional intermol. interactions. It is operative in detg. mol. conformation, mol. aggregation, and the function of a vast no. of chem. systems ranging from inorg. to biol. Research into hydrogen bonds experienced a stagnant period in the 1980s but re-opened around 1990, and has been in rapid development since then. In terms of modern concepts, the hydrogen bond is understood as a very broad phenomenon, and it is accepted that there are open borders to other effects. There are dozens of different types of X-H···A hydrogen bonds that occur commonly in the condensed phases, and in addn. there are innumerable less common ones. Dissocn. energies span more than two orders of magnitude (about 02.-40 kcal mol-1). Within this range, the nature of the interaction is not const., but its electrostatic, covalent, and dispersion contributions vary in their relative wts. The hydrogen bond has broad transition regions that merge continuously with the covalent bond, the van der Waals interaction, the ionic interaction, and also the cation-π interaction. All hydrogen bonds can be considered as incipient proton transfer reactions, and for strong hydrogen bonds, this reaction can be in a very advanced state. In this review, a coherent survey is given on all these matters.
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  25. 25
    Whale, T. F.; Rosillo-Lopez, M.; Murray, B. J.; Salzmann, C. G. Ice Nucleation Properties of Oxidized Carbon Nanomaterials. J. Phys. Chem. Lett. 2015, 6, 3012– 3016,  DOI: 10.1021/acs.jpclett.5b01096
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    25
    Ice Nucleation Properties of Oxidized Carbon Nanomaterials
    Whale, Thomas F.; Rosillo-Lopez, Martin; Murray, Benjamin J.; Salzmann, Christoph G.
    Journal of Physical Chemistry Letters (2015), 6 (15), 3012-3016CODEN: JPCLCD; ISSN:1948-7185. (American Chemical Society)
    Heterogeneous ice nucleation is an important process in many fields, particularly atm. science, but is still poorly understood. All known inorg. ice nucleating particles are relatively large in size and tend to be hydrophilic. Hence it is not obvious that carbon nanomaterials should nucleate ice. However, in this paper we show that four different readily water-dispersible carbon nanomaterials are capable of nucleating ice. The tested materials were carboxylated graphene nanoflakes, graphene oxide, oxidized single walled carbon nanotubes and oxidized multiwalled carbon nanotubes. The carboxylated graphene nanoflakes have a diam. of ∼30 nm and are among the smallest entities obsd. so far to nucleate ice. Overall, carbon nanotubes were found to nucleate ice more efficiently than flat graphene species, and less oxidized materials nucleated ice more efficiently than more oxidized species. These well-defined carbon nanomaterials may pave the way to bridging the gap between exptl. and computational studies of ice nucleation.
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  26. 26
    Lupi, L.; Hudait, A.; Molinero, V. Heterogeneous Nucleation of Ice on Carbon Surfaces. J. Am. Chem. Soc. 2014, 136, 3156– 3164,  DOI: 10.1021/ja411507a
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    26
    Heterogeneous Nucleation of Ice on Carbon Surfaces
    Lupi, Laura; Hudait, Arpa; Molinero, Valeria
    Journal of the American Chemical Society (2014), 136 (8), 3156-3164CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
    Atm. aerosols can promote the heterogeneous nucleation of ice, impacting the radiative properties of clouds and Earth's climate. The exptl. study of heterogeneous freezing of water droplets by carbonaceous particles reveals widespread ice freezing temps. It is not known which structural and chem. characteristics of soot account for the variability in ice nucleation efficiency. Here the authors use mol. dynamics simulations to study the nucleation of ice from liq. water in contact with graphitic surfaces. Atomically flat carbon surfaces promote heterogeneous nucleation of ice, while molecularly rough surfaces with the same hydrophobicity do not. Graphitic surfaces and other surfaces that promote ice nucleation induce layering in the interfacial water, suggesting that the order imposed by the surface on liq. water may play an important role in the heterogeneous nucleation mechanism. The authors study a large set of graphitic surfaces of various dimensions and radii of curvature and find that variations in nanostructures alone could account for the spread in the freezing temps. of ice on soot in expts. A characterization of the nanostructure of soot is needed to predict its ice nucleation efficiency.
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  27. 27
    Biggs, C. I.; Packer, C.; Hindmarsh, S.; Walker, M.; Wilson, N. R.; Rourke, J. P.; Gibson, M. I. Impact of Sequential Surface-Modification of Graphene Oxide on Ice Nucleation. Phys. Chem. Chem. Phys. 2017, 19, 21929– 21932,  DOI: 10.1039/c7cp03219f
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    27
    Impact of sequential surface-modification of graphene oxide on ice nucleation
    Biggs, Caroline I.; Packer, Christopher; Hindmarsh, Steven; Walker, Marc; Wilson, Neil R.; Rourke, Jonathan P.; Gibson, Matthew I.
    Physical Chemistry Chemical Physics (2017), 19 (33), 21929-21932CODEN: PPCPFQ; ISSN:1463-9076. (Royal Society of Chemistry)
    Base-washed graphene-oxide which has been sequentially-modified by thiol-epoxy chem., results in materials with ice-nucleation activity. The role of hydrophilic and hydrophobic grafts and polymers was evaluated with the most potent functioning at just 0.25 wt.%. These 2D hybrid materials may find use in cryopreservation and fundamental studies on ice formation.
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  28. 28
    Behera, S. N.; Sharma, M. Investigating the Potential Role of Ammonia in Ion Chemistry of Fine Particulate Matter Formation for an Urban Environment. Sci. Total Environ. 2010, 408, 3569– 3575,  DOI: 10.1016/j.scitotenv.2010.04.017
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    28
    Investigating the potential role of ammonia in ion chemistry of fine particulate matter formation for an urban environment
    Behera, Sailesh N.; Sharma, Mukesh
    Science of the Total Environment (2010), 408 (17), 3569-3575CODEN: STENDL; ISSN:0048-9697. (Elsevier B.V.)
    To assess the potential role of NH3 in ion chem. of PM2.5 aerosols, measurements of PM2.5 (particulate matter with aerodynamic diam. <2.5 μm) along with its ionic speciation and gaseous pollutants (SO2, NOx, NH3, HNO3) were made in summer and winter, 2007-2008, at 4 sample sites in Kanpur, an urban-industrial city in the Ganga Basin, India. Mean concns. of water-sol. ions were obsd. in the following order: summer: SO42-, 26.3 μg/m3 > NO3-, 16.8 μg/m3 > NH4+, 15.1 μg/m3 > Ca2+, 4.1 μg/m3 > Na+, 2.4 μg/m3 > K+, 2.1 μg/m3; and winter: SO42-, 28.9 μg/m3 > NO3-, 23.0 μg/m3 > NH4+, 16.4 μg/m3 > Ca2+, 3.4 μg/m3 > K+, 3.3 μg/m3 > Na+, 3.2 μg/m3. The mean molar NH4+:SO42- molar ratio, 2.8 ± 0.6 (mostly >2), indicated the abundance of NH3 to neutralize H2SO4. Excess NH4+ was inferred to be assocd. with NO3- and Cl-. A higher S (Fs, 58%) vs. N conversion ratios (Fn: 39%) indicated SO42- were the preferred secondary species to NO3-. The charge balance for the PM2.5 ion chem. showed that compds. formed from an NH3 precursor were (NH4)2SO4, NH4NO3, and NH4Cl. Results conclusively established that while there are higher contributions of NH4+ and SO42- to PM2.5 in summer, particulate NO3- have higher winter contributions, crit. due to low temp.-driven reactions between NH3 and HNO3 in a forward direction for enhanced NO3- formation. Inorg. secondary aerosol formation accounted for 30% of the PM2.5 mass; thus, any particulate control strategy should include optimal control of primary precursor gases including NH3.
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  29. 29
    Pandolfi, M.; Amato, F.; Reche, C.; Alastuey, A.; Otjes, R. P.; Blom, M. J.; Querol, X. Summer Ammonia Measurements in a Densely Populated Mediterranean City. Atmos. Chem. Phys. 2012, 12, 7557– 7575,  DOI: 10.5194/acp-12-7557-2012
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    29
    Summer ammonia measurements in a densely populated Mediterranean city
    Pandolfi, M.; Amato, F.; Reche, C.; Alastuey, A.; Otjes, R. P.; Blom, M. J.; Querol, X.
    Atmospheric Chemistry and Physics (2012), 12 (16), 7557-7575CODEN: ACPTCE; ISSN:1680-7316. (Copernicus Publications)
    Real-time measurements of ambient concns. of gas-phase ammonia (NH3) were performed in Barcelona (NE Spain) in summer between May and Sept. 2011. Two measurement sites were selected: one in an urban background traffic-influenced area (UB) and the other in the historical city center (CC). Levels of NH3 were higher at CC (5.6 ± 2.1 μg m-3 or 7.5 ± 2.8 ppbv) compared with UB (2.2 ± 1.0 μg m-3 or 2.9 ± 1.3 ppbv). This difference is attributed to the contribution from non-traffic sources such as waste containers, sewage systems, humans and open markets more dense in the densely populated historical city center. Under high temps. in summer these sources had the potential to increase the ambient levels of NH3 well above the urban-background-traffic-influenced UB measurement station. Measurements were used to assess major local emissions, sinks and diurnal evolution of NH3. The measured levels of NH3, esp. high in the old city, may contribute to the high mean annual concns. of secondary sulfate and nitrate measured in Barcelona compared with other cities in Spain affected by high traffic intensity. Ancillary measurements, including PM10, PM2.5, PM1 levels (Particulate Matter with aerodynamic diam. smaller than 10 μm, 2.5 μm, and 1 μm), gases and black carbon concns. and meteorol. data, were performed during the measurement campaign. The anal. of specific periods (3 special cases) during the campaign revealed that road traffic was a significant source of NH3. However, its effect was more evident at UB compared with CC where it was masked given the high levels of NH3 from non-traffic sources measured in the old city. The relationship between SO2-4 daily concns. and gas-fraction ammonia (NH3/(NH3 + NH+4)) revealed that the gas-to-particle phase partitioning (volatilization or ammonium salts formation) also played an important role in the evolution of NH3 concn. in summer in Barcelona.
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  30. 30
    Phan, N.-T.; Kim, K.-H.; Shon, Z.-H.; Jeon, E.-C.; Jung, K.; Kim, N.-J. Analysis of Ammonia Variation in the Urban Atmosphere. Atmos. Environ. 2013, 65, 177– 185,  DOI: 10.1016/j.atmosenv.2012.10.049
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    30
    Analysis of ammonia variation in the urban atmosphere
    Phan, Nhu-Thuc; Kim, Ki-Hyun; Shon, Zang-Ho; Jeon, Eui-Chan; Jung, Kweon; Kim, Nam-Jin
    Atmospheric Environment (2013), 65 (), 177-185CODEN: AENVEQ; ISSN:1352-2310. (Elsevier Ltd.)
    Long-term monitoring of NH3 concn. and other trace gases was made at hourly intervals along with meteorol. parameters in Seoul, Korea for a 1-yr period (1 Sept. 2010-23 August 2011). The mean NH3 concns. measured at 2 sites (Gwang-Jin (GJ) and Gang-Seo (GS) districts) were 10.9 ± 4.25 and 12.3 ± 4.23 ppb, resp. A comparison of the seasonal data shows its relative dominance at both GJ and GS sites during the warm period (summer and spring) over the cool period (winter and fall). Likewise, over the diurnal scale, relative dominance during daytime was also apparent (p < 0.05). A comparison between different studies suggests that the long-term trend of NH3 levels should be tightly affected by an increasing no. of vehicles. As such, the results of the statistical anal. also point to the potentially significant role of traffic activities in the elevation of NH3 levels in urban areas.
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  31. 31
    Hauptmann, A.; Handle, K. F.; Baloh, P.; Grothe, H.; Loerting, T. Does the Emulsification Procedure Influence Freezing and Thawing of Aqueous Droplets?. J. Chem. Phys. 2016, 145, 211923,  DOI: 10.1063/1.4965434
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    Pummer, B. G.; Bauer, H.; Bernardi, J.; Bleicher, S.; Grothe, H. Suspendable Macromolecules Are Responsible for Ice Nucleation Activity of Birch and Conifer Pollen. Atmos. Chem. Phys. 2012, 12, 2541– 2550,  DOI: 10.5194/acp-12-2541-2012
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    32
    Suspendable macromolecules are responsible for ice nucleation activity of birch and conifer pollen
    Pummer, B. G.; Bauer, H.; Bernardi, J.; Bleicher, S.; Grothe, H.
    Atmospheric Chemistry and Physics (2012), 12 (5), 2541-2550CODEN: ACPTCE; ISSN:1680-7316. (Copernicus Publications)
    The ice nucleation of bioaerosols (bacteria, pollen, spores, etc.) is a topic of growing interest, since their impact on ice cloud formation and thus on radiative forcing, an important parameter in global climate, is not yet fully understood. Here we show that pollen of different species strongly differ in their ice nucleation behavior. The av. freezing temps. in lab. expts. range from 240 to 255 K. As the most efficient nuclei (silver birch, Scots pine and common juniper pollen) have a distribution area up to the Northern timberline, their ice nucleation activity might be a cryoprotective mechanism. Far more intriguingly, it has turned out that water, which has been in contact with pollen and then been sepd. from the bodies, nucleates as good as the pollen grains themselves. The ice nuclei have to be easily-suspendable macromols. located on the pollen. Once extd., they can be distributed further through the atm. than the heavy pollen grains and so presumably augment the impact of pollen on ice cloud formation even in the upper troposphere. Our expts. lead to the conclusion that pollen ice nuclei, in contrast to bacterial and fungal ice nucleating proteins, are non-proteinaceous compds.
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  33. 33
    Zolles, T.; Burkart, J.; Häusler, T.; Pummer, B.; Hitzenberger, R.; Grothe, H. Identification of Ice Nucleation Active Sites on Feldspar Dust Particles. J. Phys. Chem. A 2015, 119, 2692– 2700,  DOI: 10.1021/jp509839x
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    Identification of ice nucleation active sites on feldspar dust particles
    Zolles, Tobias; Burkart, Julia; Haeusler, Thomas; Pummer, Bernhard; Hitzenberger, Regina; Grothe, Hinrich
    Journal of Physical Chemistry A (2015), 119 (11), 2692-2700CODEN: JPCAFH; ISSN:1089-5639. (American Chemical Society)
    Mineral dusts originating from Earth's crust are known to be important atm. ice nuclei. In agreement with earlier studies, feldspar was found as the most active of the tested natural mineral dusts. Here we investigated in closer detail the reasons for its activity and the difference in the activity of the different feldspars. Conclusions are drawn from SEM, X-ray powder diffraction, IR spectroscopy, and oil-immersion freezing expts. K-feldspar showed by far the highest ice nucleation activity. Finally, we give a potential explanation of this effect, finding alkali-metal ions having different hydration shells and thus an influence on the ice nucleation activity of feldspar surfaces.
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  34. 34
    Johnson, D. W.; Dobson, B. P.; Coleman, K. S. A Manufacturing Perspective on Graphene Dispersions. Curr. Opin. Colloid Interface Sci. 2015, 20, 367– 382,  DOI: 10.1016/j.cocis.2015.11.004
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    A manufacturing perspective on graphene dispersions
    Johnson, David W.; Dobson, Ben P.; Coleman, Karl S.
    Current Opinion in Colloid & Interface Science (2015), 20 (5-6), 367-382CODEN: COCSFL; ISSN:1359-0294. (Elsevier Ltd.)
    Harnessing the exceptional phys. properties of graphene often requires its dispersion into aq. or org. media. Dispersion must be achieved at a concn. and stability appropriate to the final application. However, the strong interaction between graphene sheets means it disperses poorly in all but a few high boiling org. solvents. This review presents an overview of graphene dispersion applications and a discussion of dispersion strategies: in particular the effect of shear, solvent and chem. modification on the dispersion of graphene (including graphene oxide and reduced graphene oxide). These techniques are discussed in the context of manufg. and commercialization.
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    Konios, D.; Stylianakis, M. M.; Stratakis, E.; Kymakis, E. Dispersion Behaviour of Graphene Oxide and Reduced Graphene Oxide. J. Colloid Interface Sci. 2014, 430, 108– 112,  DOI: 10.1016/j.jcis.2014.05.033
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    Dispersion behaviour of graphene oxide and reduced graphene oxide
    Konios, Dimitrios; Stylianakis, Minas M.; Stratakis, Emmanuel; Kymakis, Emmanuel
    Journal of Colloid and Interface Science (2014), 430 (), 108-112CODEN: JCISA5; ISSN:0021-9797. (Elsevier B.V.)
    The dispersion behavior of graphene oxide (GO) and chem. reduced GO (rGO) has been investigated in a wide range of org. solvents. The effect of the redn. process on the GO soly. in eighteen different solvents was examd. and analyzed, taking into consideration the solvent polarity, the surface tension and the Hansen and Hildebrand soly. parameters. rGO concns. up to ∼9 μg/mL in chlorinated solvents were achieved, demonstrating an efficient solubilization strategy, extending the scope for scalable liq.-phase processing of conductive rGO inks for the development of printed flexible electronics.
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  36. 36
    Broadley, S. L.; Murray, B. J.; Herbert, R. J.; Atkinson, J. D.; Dobbie, S.; Malkin, T. L.; Condliffe, E.; Neve, L. Immersion Mode Heterogeneous Ice Nucleation by an Illite Rich Powder Representative of Atmospheric Mineral Dust. Atmos. Chem. Phys. 2012, 12, 287– 307,  DOI: 10.5194/acp-12-287-2012
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    Immersion mode heterogeneous ice nucleation by an illite rich powder representative of atmospheric mineral dust
    Broadley, S. L.; Murray, B. J.; Herbert, R. J.; Atkinson, J. D.; Dobbie, S.; Malkin, T. L.; Condliffe, E.; Neve, L.
    Atmospheric Chemistry and Physics (2012), 12 (1), 287-307CODEN: ACPTCE; ISSN:1680-7316. (Copernicus Publications)
    Atm. dust rich in illite is transported globally from arid regions and impacts cloud properties through the nucleation of ice. We present measurements of ice nucleation in water droplets contg. known quantities of an illite rich powder under atmospherically relevant conditions. The illite rich powder used here, NX illite, has a similar mineralogical compn. to atm. mineral dust sampled in remote locations, i.e. dust which has been subject to long range transport, cloud processing and sedimentation. Arizona Test Dust, which is used in other ice nucleation studies as a model atm. dust, has a significantly different mineralogical compn. and we suggest that NX illite is a better surrogate of natural atm. dust. Using optical microscopy, heterogeneous nucleation in the immersion mode by NX illite was obsd. to occur dominantly between 246 K and the homogeneous freezing limit. In general, higher freezing temps. were obsd. when larger surface areas of NX illite were present within the drops. Homogenous nucleation was obsd. to occur in droplets contg. low surface areas of NX illite. We show that NX illite exhibits strong particle to particle variability in terms of ice nucleating ability, with ∼1 in 105 particles dominating ice nucleation when high surface areas were present. In fact, this work suggests that the bulk of atm. mineral dust particles may be less efficient at nucleating ice than assumed in current model parameterisations. For droplets contg. ≤2 × 10-6 cm2 of NX illite, freezing temps. did not noticeably change when the cooling rate was varied by an order of magnitude. The data obtained during cooling expts. (surface area ≤2 × 10-6 cm2) is shown to be inconsistent with the single component stochastic model, but is well described by the singular model (ns(236.2 K ≤T ≤247.5 K) = exp(6.53043 × 104 - 8.2153088 × 102T + 3.446885376T2 - 4.822268 × 10-3T3). However, droplets continued to freeze when the temp. was held const., which is inconsistent with the time independent singular model. We show that this apparent discrepancy can be resolved using a multiple component stochastic model in which it is assumed that there are many types of nucleation sites, each with a unique temp. dependent nucleation coeff. Cooling rate independence can be achieved with this time dependent model if the nucleation rate coeffs. increase very rapidly with decreasing temp., thus reconciling our measurement of nucleation at const. temp. with the cooling rate independence.
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    Connolly, P. J.; Möhler, O.; Field, P. R.; Saathoff, H.; Burgess, R.; Choularton, T.; Gallagher, M. Studies of Heterogeneous Freezing by Three Different Desert Dust Samples. Atmos. Chem. Phys. 2009, 9, 2805– 2824,  DOI: 10.5194/acp-9-2805-2009
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    Studies of heterogeneous freezing by three different desert dust samples
    Connolly, P. J.; Mohler, O.; Field, P. R.; Saathoff, H.; Burgess, R.; Choularton, T.; Gallagher, M.
    Atmospheric Chemistry and Physics (2009), 9 (8), 2805-2824CODEN: ACPTCE; ISSN:1680-7316. (Copernicus Publications)
    We present results of expts. at the aerosol interactions and dynamics in the atm. (AIDA) chamber facility looking at the freezing of water by three different types of mineral particles at temps. between -12 and -33°C. The three different dusts are Asia Dust-1 (AD1), Sahara Dust-2 (SD2) and Arizona test Dust (ATD). The dust samples used had particle concns. of sizes that were log-normally distributed with mode diams. between 0.3 and 0.5 μm and std. deviations, σg, of 1.6-1.9. The results from the freezing expts. are consistent with the singular hypothesis of ice nucleation. The dusts showed different nucleation abilities, with ATD showing a rather sharp increase in ice-active surface site d. at temps. less than -24°C. AD1 was the next most efficient freezing nuclei and showed a more gradual increase in activity than the ATD sample. SD2 was the least active freezing nuclei. We used data taken with particle counting probes to derive the ice-active surface site d. forming on the dust as a function of temp. for each of the three samples and polynomial curves are fitted to this data. The curve fits are then used independently within a bin microphys. model to simulate the ice formation rates from the expts. in order to test the validity of parameterizing the data with smooth curves. Good agreement is found between the measurements and the model for AD1 and SD2; however, the curve for ATD does not yield results that agree well with the observations. The reason for this is that more expts. between -20 and -24°C are needed to quantify the rather sharp increase in ice-active surface site d. on ATD in this temp. regime. The curves presented can be used as parameterizations in atm. cloud models where cooling rates of approx. 1 °C min-1 or more are present to predict the concn. of ice crystals forming by the condensation-freezing mode of ice nucleation. Finally a polynomial is fitted to all three samples together in order to have a parameterization describing the av. ice-active surface site d. vs. temp. for an equal mixt. of the three dust samples.
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  38. 38
    DeMott, P. J. Quantitative Descriptions of Ice Formation Mechanisms of Silver Iodide-Type Aerosols. Atmos. Res. 1995, 38, 63– 99,  DOI: 10.1016/0169-8095(94)00088-u
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    Quantitative descriptions of ice formation mechanisms of silver iodide-type aerosols
    DeMott, P.J.
    Atmospheric Research (1995), 38 (1-4), 63-99CODEN: ATREEW; ISSN:0169-8095. (Elsevier)
    Lab. and numerical cloud model expts. were designed to obtain quant. data describing ice formation by two specific aerosols used operationally for cloud modification. Exptl. methodologies and a quant. framework for predicting ice formation by these silver iodide-based aerosols were based on four currently accepted nucleation mechanisms (modes) and their inherent dependencies on the varied temp., pressure, humidity, and cloud conditions that can be encountered in the atm. The processes considered were deposition, condensation freezing, contact freezing and immersion freezing nucleation. Particle size dependencies were also quantified. The Colorado State University dynamic (controlled expansion) cloud chamber was used to reproduce atm. cloud conditions exptl. An adiabatic cloud model was adapted for equiv. simulation of cloud chamber expts. Hydrophobic AgI-AgCl and hygroscopic AgI-AgCl-4NaCl aerosols were found to function by some combination of all four nucleation mechanisms. AgI-AgCl aerosols were found to be potentially most efficient as contact freezing nuclei, but slow collision rates between IN and cloud droplets permit deposition and condensation freezing nucleation to become important for many cloud conditions. Condensation freezing was seen to progressively dominate ice formation when AgI-AgCl aerosols were exposed to increasing supersatn. with respect to water in the typical atm. range (up to 1%). Immersion freezing nucleation was always less efficient than contact freezing. The hygroscopic AgI-AgCl-4NaCl aerosols displayed deposition and condensation freezing active site densities about one order of magnitude higher than the AgI-AgCl aerosols, while contact freezing activity was not discernable. Immersion freezing could be as important or more important than condensation freezing nucleation for these hygroscopic aerosols depending on cloud characteristics and how aerosols are released into cloud. Instantaneous exposure of either ice nucleus aerosol to high water supersaturations caused the dominance of the immersion freezing mechanism. Quant. results were formulated for use in numerical cloud modeling. Ice crystal formation subsequently predicted in cloud model simulations showed good agreement with ice formation measured in cloud chamber simulations of relevant cloud seeding methodologies.
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    Niedermeier, D.; Hartmann, S.; Shaw, R. A.; Covert, D.; Mentel, T. F.; Schneider, J.; Poulain, L.; Reitz, P.; Spindler, C.; Clauss, T. Heterogeneous Freezing of Droplets with Immersed Mineral Dust Particles—Measurements and Parameterization. Atmos. Chem. Phys. 2010, 10, 3601– 3614,  DOI: 10.5194/acp-10-3601-2010
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    Edwards, G. R.; Evans, L. F.; La Mer, V. K. Ice Nucleation by Monodisperse Silver Iodide Particles. J. Colloid Sci. 1962, 17, 749– 758,  DOI: 10.1016/0095-8522(62)90049-1
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    Ice nucleation by monodisperse silver iodide particles
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    Ice nucleation was studied by using monodisperse AgI sols. prepd. by the decompn. of the complex formed by dissolving AgI in strong aq. solns. of KI. Microscopic observations were made of the temp. at which 50% of the droplets had frozen, and of the no. of AgI particles in contact with each droplet. The nucleation temp. depended on the no. of particles in contact with the drop, indicating that particles of one size and crystal form are not equally active as freezing nuclei, but that the frequency of occurrence of nucleating sites on a given particle is proportional to the surface area. It is proposed that the activity of various AgI prepns. should be quoted in terms of the probability that a given nucleation site should occur on a particle of given size.
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    A technique for quantifying heterogeneous ice nucleation in microlitre supercooled water droplets
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  • Abstract

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    Figure 1

    Figure 1. Representative chemical structures of the samples investigated: (a) nonfunctionalized graphene G-non, (44) (b) covalently functionalized graphene G-NPr3+X– (X = I and OH), (c) graphene oxide nanocolloids GO-nano, (d) graphene oxide GO-DE and GO-SA, (45) and (e) ammonia-functionalized graphene oxide GO-ammo. According to the provided datasheet of the purchased material from Sigma-Aldrich Chemistry.

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    Figure 2

    Figure 2. (a) Ratio of frozen droplets fice and (b) the ice nucleation active surface site density ns at a given temperature for all investigated samples. The ns value, the freezing temperature range, and the ns trend provide key information on the characteristics of the ice-nucleation-active samples of graphene or graphene oxides. Some droplets nucleate at about −36 °C, meaning that they do not contain INPs. Experimental uncertainty in the ns value was calculated by changes in the weight and droplet size.

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    Figure 3

    Figure 3. Raman spectra of (a) all investigated graphene samples and (b) nonfunctionalized graphene (G-non); first-order curve fitted with band combination according to Table 1 (λ0 = 633 nm).

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    Figure 4

    Figure 4. TEM images of graphene samples investigated: (a) nonfunctionalized graphene (G-non) indicates flakes with diameters of up to 400 nm and with up to 7 layers (46) and (b) covalently functionalized graphene (G-NPr3+I– and G-NPr3+OH–) shows the same layer size and thickness as its nonfunctionalized precursor G-non but also shows individual sheets accumulating into larger “fluffy” aggregates.

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    Figure 5

    Figure 5. Raman spectra of (a) all investigated graphene oxide samples and (b) GO-NH2; first-order curve fitted with band combination according to Table 1 (λ0 = 633 nm).

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    Figure 6

    Figure 6. TEM images of the samples investigated: (a) nonfunctionalized (GO-SA and GO-DE) and ammonia-functionalized graphene oxides (GO-NH2) reveal large flakes of approximately 5 nm thickness and several micrometers in diameter, and the thickness of the sheets and number of signals in the corresponding electron diffraction pattern indicate multi-layer graphene composed of 2–7 layers, while (b) GO-nano consists of particles of varying shapes with sizes of up to 200 nm and thickness of at least 3 nm.

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    This article references 49 other publications.

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      Koop, T.; Luo, B.; Tsias, A.; Peter, T. Water Activity as the Determinant for Homogeneous Ice Nucleation in Aqueous Solutions. Nature 2000, 406, 611– 614,  DOI: 10.1038/35020537
      1
      Water activity as the determinant for homogeneous ice nucleation in aqueous solutions
      Koop, Thomas; Luo, Belping; Tsias, Athanaslos; Peter, Thomas
      Nature (London) (2000), 406 (6796), 611-614CODEN: NATUAS; ISSN:0028-0836. (Nature Publishing Group)
      The unique properties of water in the supercooled (metastable) state are not fully understood. In particular, the effects of solutes and mech. pressure on the kinetics of the liq.-to-solid phase transition of supercooled water and aq. solns. to ice have remained unresolved. Here we show from exptl. data that the homogeneous nucleation of ice from supercooled aq. solns. is independent of the nature of the solute, but depends only on the water activity of the soln. - i.e., the ratio between the water vapor pressures of the soln. and of pure water under the same conditions. In addn., the presence of solutes and the application of pressure have a very similar effect on ice nucleation. We present a thermodn. theory for homogeneous ice nucleation, which expresses the nucleation rate coeff. as a function of water activity and pressure. Recent observations from clouds contg. ice are in good agreement with our theory and our results should help to overcome one of the main weaknesses of numerical models of the atm., the formulation of cloud processes.
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      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD3cXmtFegtbo%253D&md5=43202e00c7d6c4919fe2743c963946b1
    2. 2
      Möhler, O.; Stetzer, O.; Schaefers, S.; Linke, C.; Schnaiter, M.; Tiede, R.; Saathoff, H.; Krämer, M.; Mangold, A.; Budz, P. Experimental Investigation of Homogeneous Freezing of Sulphuric Acid Particles in the Aerosol Chamber Aida. Atmos. Chem. Phys. 2003, 3, 211– 223,  DOI: 10.5194/acp-3-211-2003
      There is no corresponding record for this reference.
    3. 3
      Pruppacher, H. R.; Klett, J. D. Microphysics of Clouds and Precipitation; Kluwer Academic Publishers: Dordrecht, 1997.
      There is no corresponding record for this reference.
    4. 4
      Szyrmer, W.; Zawadzki, I. Biogenic and Anthropogenic Sources of Ice-Forming Nuclei: A Review. B. Bull. Am. Meteorol. Soc. 1997, 78, 209– 228,  DOI: 10.1175/1520-0477(1997)078<0209:baasoi>2.0.co;2
      There is no corresponding record for this reference.
    5. 5
      Murray, B. J.; O’Sullivan, D.; Atkinson, J. D.; Webb, M. E. Ice Nucleation by Particles Immersed in Supercooled Cloud Droplets. Chem. Soc. Rev. 2012, 41, 6519– 6554,  DOI: 10.1039/c2cs35200a
      5
      Ice nucleation by particles immersed in supercooled cloud droplets
      Murray, B. J.; O'Sullivan, D.; Atkinson, J. D.; Webb, M. E.
      Chemical Society Reviews (2012), 41 (19), 6519-6554CODEN: CSRVBR; ISSN:0306-0012. (Royal Society of Chemistry)
      A review. The formation of ice particles in the Earth's atm. strongly affects the properties of clouds and their impact on climate. Despite the importance of ice formation in detg. the properties of clouds, the Intergovernmental Panel on Climate Change (IPCC, 2007) was unable to assess the impact of atm. ice formation in their most recent report because our basic knowledge is insufficient. Part of the problem is the paucity of quant. information on the ability of various atm. aerosol species to initiate ice formation. Here we review and assess the existing quant. knowledge of ice nucleation by particles immersed within supercooled water droplets. We introduce aerosol species which have been identified in the past as potentially important ice nuclei and address their ice-nucleating ability when immersed in a supercooled droplet. We focus on mineral dusts, biol. species (pollen, bacteria, fungal spores and plankton), carbonaceous combustion products and volcanic ash. In order to make a quant. comparison we first introduce several ways of describing ice nucleation and then summarise the existing information according to the time-independent (singular) approxn. Using this approxn. in combination with typical atm. loadings, we est. the importance of ice nucleation by different aerosol types. According to these ests. we find that ice nucleation below about -15 °C is dominated by soot and mineral dusts. Above this temp. the only materials known to nucleate ice are biol., with quant. data for other materials absent from the literature. We conclude with a summary of the challenges our community faces.
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    6. 6
      Lin, R.-F.; Starr, D. O.; DeMott, P. J.; Cotton, R.; Sassen, K.; Jensen, E.; Kärcher, B.; Liu, X. Cirrus Parcel Model Comparison Project. Phase 1: The Critical Components to Simulate Cirrus Initiation Explicitly. J. Atmos. Sci. 2002, 59, 2305– 2329,  DOI: 10.1175/1520-0469(2002)059<2305:cpmcpp>2.0.co;2
      There is no corresponding record for this reference.
    7. 7
      Chang, S. G.; Novakov, T. Formation of Pollution Particulate Nitrogen-Compounds by No-Soot and Nh3-Soot Gas-Particle Surface-Reactions. Atmos. Environ. 1975, 9, 495– 504,  DOI: 10.1016/0004-6981(75)90109-2
      There is no corresponding record for this reference.
    8. 8
      Novakov, T.; Chang, S. G.; Harker, A. B. Sulfates as Pollution Particulates: Catalytic Formation on Carbon (Soot) Particles. Science 1974, 186, 259– 261,  DOI: 10.1126/science.186.4160.259
      8
      Sulfates as pollution particulates. Catalytic formation on carbon (soot) particles
      Novakov, T.; Chang, S. G.; Harker, A. B.
      Science (Washington, DC, United States) (1974), 186 (4160), 259-61CODEN: SCIEAS; ISSN:0036-8075.
      Exptl. evidence (obtained by electron spectroscopy for chem. anal.) is presented which shows that finely divided C (soot) particles may play a major role in the catalytic oxidn. of SO2 to sulfate in polluted atms. The results obtained with sulfates produced in the lab. by the oxidn. of SO2 on graphite particles and combustion-produced soot particles are compared with the properties and behavior of ambient sulfates. The proposed SO2 oxidn. mechanism is qual. consistent with field observation.
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    9. 9
      Rosen, H.; Hansen, A. D. A.; Dod, R. L.; Novakov, T. Soot in Urban Atmospheres: Determination by an Optical-Absorption Technique. Science 1980, 208, 741– 744,  DOI: 10.1126/science.208.4445.741
      There is no corresponding record for this reference.
    10. 10
      DeMott, P. J. An Exploratory-Study of Ice Nucleation by Soot Aerosols. J. Appl. Meteorol. 1990, 29, 1072– 1079,  DOI: 10.1175/1520-0450(1990)029<1072:aesoin>2.0.co;2
      There is no corresponding record for this reference.
    11. 11
      Dymarska, M.; Murray, B. J.; Sun, L.; Eastwood, M. L.; Knopf, D. A.; Bertram, A. K. Deposition Ice Nucleation on Soot at Temperatures Relevant for the Lower Troposphere. J. Geophys. Res.: Atmos. 2006, 111, D04204,  DOI: 10.1029/2005jd006627
      11
      Deposition ice nucleation on soot at temperatures relevant for the lower troposphere
      Dymarska, Magdalena; Murray, Benjamin J.; Sun, Limin; Eastwood, Michael L.; Knopf, Daniel A.; Bertram, Allan K.
      Journal of Geophysical Research, [Atmospheres] (2006), 111 (D4), D04204/1-D04204/9CODEN: JGRDE3 ISSN:. (American Geophysical Union)
      The ice nucleating efficiency of many important atm. particles remains poorly understood. Here we investigate the ice nucleation properties of a range of soot types including soot that has been treated with atmospherically relevant amts. of ozone. We focus on deposition nucleation below water satn. and at temps. ranging from 243 to 258 K. For our exptl. conditions, ice nucleation never occurred at temps. above 248 K and below water satn. Below 248 K, ice occasionally formed in our expts. with no indication of the formation of water droplets prior to ice formation. However, even at these temps. the relative humidity with respect to ice (RHi) was close to water satn. when ice nucleation was obsd., suggesting water nucleation may have occurred first followed by ice nucleation during the condensation process. We also performed a complimentary set of expts. where we held soot particles at 248 K and RHi = 124 ± 4%, which is just below water satn., for a period of 8 h. From these measurements we calcd. an upper limit of the heterogeneous ice nucleation rate coeff. of 0.1 cm-2 s-1. If the no. of soot particles is 1.5 × 105 L-1 in the atm. (which corresponds to urban-influenced rural areas), then the no. of ice particles produced below water satn. at these conditions is at most 0.1 particles L-1 on the basis of our upper limit. We conclude from our studies that deposition nucleation of ice on most types of soot particles is not important in the Earth's troposphere above 243 K and below water satn.
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    12. 12
      Friedman, B.; Kulkarni, G.; Beránek, J.; Zelenyuk, A.; Thornton, J. A.; Cziczo, D. J. Ice Nucleation and Droplet Formation by Bare and Coated Soot Particles. J. Geophys. Res.: Atmos. 2011, 116, D17203,  DOI: 10.1029/2011jd015999
      12
      Ice nucleation and droplet formation by bare and coated soot particles
      Friedman, Beth; Kulkarni, Gourihar; Beranek, Josef; Zelenyuk, Alla; Thornton, Joel A.; Cziczo, Daniel J.
      Journal of Geophysical Research: Atmospheres (2011), 116 (Sept.), D17203/1-D17203/11CODEN: JGRDE3 ISSN:. (American Geophysical Union)
      We have studied ice formation at temps. relevant to homogeneous and heterogeneous ice nucleation, as well as droplet activation and hygroscopicity, of soot particles of variable size and compn. Coatings of adipic, malic, and oleic acid were applied in order to span an atmospherically relevant range of soly., and both uncoated and oleic acid coated soot particles were exposed to ozone in order to simulate atm. oxidn. The results are interpreted in terms of onset ice nucleation, with a comparison to a mineral dust particle that acts as an efficient ice nucleus, and particle hygroscopicity. At 253 K and 243 K, we found no evidence of heterogeneous ice nucleation occurring above the level of detection for our exptl. conditions. Above water satn., only droplet formation was obsd. At 233 K, we observe the occurrence of homogeneous ice nucleation for all particles studied. Coatings also did not significantly alter the ice nucleation behavior of soot particles but aided in the uptake of water. Hygroscopicity studies confirmed that pure soot particles were hydrophobic, and coated soot particles activated as droplets at high water supersaturations. A small amt. of heterogeneous ice nucleation either below the detection limit of our instrument or concurrent with droplet formation and/or homogeneous freezing cannot be precluded, but we are able to set limits for its frequency. We conclude that both uncoated and coated soot particles comparable to those generated in our studies are unlikely to significantly contribute to the global budget of heterogeneous ice nuclei at temps. between 233 K and 253 K.
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    13. 13
      Kärcher, B.; Möhler, O.; DeMott, P. J.; Pechtl, S.; Yu, F. Insights into the Role of Soot Aerosols in Cirrus Cloud Formation. Atmos. Chem. Phys. 2007, 7, 4203– 4227,  DOI: 10.5194/acp-7-4203-2007
      There is no corresponding record for this reference.
    14. 14
      Knopf, D. A.; Wang, B.; Laskin, A.; Moffet, R. C.; Gilles, M. K. Heterogeneous Nucleation of Ice on Anthropogenic Organic Particles Collected in Mexico City. Geophys. Res. Lett. 2010, 37, L11803,  DOI: 10.1029/2010gl043362
      14
      Heterogeneous nucleation of ice on anthropogenic organic particles collected in Mexico City
      Knopf, D. A.; Wang, B.; Laskin, A.; Moffet, R. C.; Gilles, M. K.
      Geophysical Research Letters (2010), 37 (11), L11803/1-L11803/5CODEN: GPRLAJ; ISSN:0094-8276. (American Geophysical Union)
      This study reports on heterogeneous ice nucleation activity of predominantly org. (or coated with org. material) anthropogenic particles sampled within and around the polluted environment of Mexico City. The onset of heterogeneous ice nucleation was obsd. as a function of particle temp. (Tp), relative humidity (RH), nucleation mode, and particle chem. compn. which is influenced by photochem. atm. aging. Particle analyses included computer controlled SEM with energy dispersive anal. of X-rays (CCSEM/EDX) and scanning transmission X-ray microscopy with near edge X-ray absorption fine structure spectroscopy (STXM/NEXAFS). In contrast to most lab. studies employing proxies of org. aerosol, we show that anthropogenic org. particles collected in Mexico City can potentially induce ice nucleation at exptl. conditions relevant to cirrus formation. The results suggest a new precedent for the potential impact of org. particles on ice cloud formation and climate.
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    15. 15
      Pratt, K. A.; Heymsfield, A. J.; Twohy, C. H.; Murphy, S. M.; DeMott, P. J.; Hudson, J. G.; Subramanian, R.; Wang, Z. E.; Seinfeld, J. H.; Prather, K. A. In Situ Chemical Characterization of Aged Biomass-Burning Aerosols Impacting Cold Wave Clouds. J. Atmos. Sci. 2010, 67, 2451– 2468,  DOI: 10.1175/2010jas3330.1
      There is no corresponding record for this reference.
    16. 16
      Zuberi, B.; Johnson, K. S.; Aleks, G. K.; Molina, L. T.; Molina, M. J.; Laskin, A. Hydrophilic Properties of Aged Soot. Geophys. Res. Lett. 2005, 32, L01807,  DOI: 10.1029/2004gl021496
      There is no corresponding record for this reference.
    17. 17
      Cooper, D. R.; D’Anjou, B.; Ghattamaneni, N.; Harack, B.; Hilke, M.; Horth, A.; Majlis, N.; Massicotte, M.; Vandsburger, L.; Whiteway, E. Experimental Review of Graphene. ISRN Condens. Matter Phys. 2012, 2012, 1– 56,  DOI: 10.5402/2012/501686
      There is no corresponding record for this reference.
    18. 18
      Richter, H.; Howard, J. B. Formation of Polycyclic Aromatic Hydrocarbons and Their Growth to Soot—a Review of Chemical Reaction Pathways. Prog. Energy Combust. Sci. 2000, 26, 565– 608,  DOI: 10.1016/s0360-1285(00)00009-5
      18
      Formation of polycyclic aromatic hydrocarbons and their growth to soot - A review of chemical reaction pathways
      Richter, H.; Howard, J. B.
      Progress in Energy and Combustion Science (2000), 26 (4-6), 565-608CODEN: PECSDO; ISSN:0360-1285. (Elsevier Science Ltd.)
      The generation by combustion processes of airborne species of current health concern, such as polycyclic arom. hydrocarbons (PAH) and soot particles, necessitates a detailed understanding of chem. reaction pathways responsible for their formation. The present review with 257 refs. discusses a general scheme of PAH formation and sequential growth of PAH by reactions with stable and radical species, including single-ring aroms., other PAH and acetylene, followed by the nucleation or inception of small soot particles, soot growth by coagulation and mass addn. from gas phase species, and carbonization of the particulate material. Exptl. and theor. tools which have allowed the achievement of deeper insight into the corresponding chem. processes are presented. The significant roles of propargyl (C3H3) and cyclopentadienyl (C5H5) radicals in the formation of first arom. rings in combustion of aliph. fuels are discussed. Detailed kinetic modeling of well-defined combustion systems, such as premixed flames, for which sufficient exptl. data for a quant. understanding are available, is of increasing importance. Reliable thermodn. and kinetic property data are also required for meaningful conclusions, and computational techniques for their detn. are presented. Routes of ongoing and future research leading to more detailed exptl. data as well as computational approaches for the exploration of elementary reaction steps and the description of systems of increasing complexity are discussed.
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    19. 19
      Böhm, H. P.; Clauss, A.; Fischer, G. O.; Hofmann, U. Das Adsorptionsverhalten Sehr Dünner Kohlenstoff-Folien. Z. Anorg. Allg. Chem. 1962, 316, 119– 127,  DOI: 10.1002/zaac.19623160303
      There is no corresponding record for this reference.
    20. 20
      Boehm, H.-P. Graphene-How a Laboratory Curiosity Suddenly Became Extremely Interesting. Angew. Chem., Int. Ed. 2010, 49, 9332– 9335,  DOI: 10.1002/anie.201004096
      20
      Graphene-How a Laboratory Curiosity Suddenly Became Extremely Interesting
      Boehm, Hanns-Peter
      Angewandte Chemie, International Edition (2010), 49 (49), 9332-9335CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)
      Once again, an allotrope of elemental carbon is at the center of intensive research. By graphene, one understands single-carbon hexagonal networks within the structure of graphite. The term was recommended by the relevant IUPAC commission on the suggestion of Eberhard Stumpp (TU Clausthal) and a subcommittee of the Working Group Carbon of the German Ceramic Society to enable characterization of the properties of single two-dimensional layers which exist independently of neighboring carbon layers. The older expression "graphite layers" is unsuitable in this respect, because a three-dimensionally arranged structure with an ABAB... stacking sequence of the layers is identified in "graphite". According to Recommended IUPAC Terminol. for the Description of Carbon as a Solid,61 the term "graphene" should only be used when reactions, structural relationships, and other properties of individual layers are discussed. However, the term "graphene" is today frequently applied to stacks of a few graphene layers, which often adhere to one another and are only partially overlapping. Graphene layers also occur in disordered carbons with turbo-static stacking, i.e., a random rotation and displacement of neighboring layers, for example, in active carbons. Similar to carbon fibers and carbon nanotubes, graphene has a very high tensile strength in the layer direction, which, together with a high flexibility, makes sharp folds in the layer possible. Their radius of curvature corresponds to that of carbon nanotubes. Interest in graphenes increased dramatically after Novoselov, Geim et al. reported on the unusual electronic properties of single layers of the graphite lattice, in other words graphene. Graphene is a semiconductor with a zero band gap and is characterized by an exceptionally high mobility of the charge carrier, a very high elec. conductance, and an unusual quantum Hall effect. It will certainly require more intensive research work before electronic components based on graphene find practical application. The prepn. of graphene layers by chem. synthesis from org. mols. that already contain condensed arom. rings (bottom-up method) promises to be an interesting development.
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    21. 21
      Lupi, L.; Molinero, V. Does Hydrophilicity of Carbon Particles Improve Their Ice Nucleation Ability?. J. Phys. Chem. A 2014, 118, 7330– 7337,  DOI: 10.1021/jp4118375
      21
      Does Hydrophilicity of Carbon Particles Improve Their Ice Nucleation Ability?
      Lupi, Laura; Molinero, Valeria
      Journal of Physical Chemistry A (2014), 118 (35), 7330-7337CODEN: JPCAFH; ISSN:1089-5639. (American Chemical Society)
      Carbonaceous particles account for 10% of the particulate matter in the atm. Atm. oxidn. and aging of soot modulates its ice nucleation ability. An increase in the ice nucleation ability of aged soot results from an increase in the hydrophilicity of the surfaces upon oxidn. Oxidn., however, also impacts the nanostructure of soot, making it difficult to assess the sep. effects of soot nanostructure and hydrophilicity in expts. Here we use mol. dynamics simulations to investigate the effect of changes in hydrophilicity of model graphitic surfaces on the freezing temp. of ice. Our results indicate that the hydrophilicity of the surface is not in general a good predictor of ice nucleation ability. We find a correlation between the ability of a surface to promote nucleation of ice and the layering of liq. water at the surface. The results of this work suggest that ordering of liq. water in contact with the surface plays an important role in the heterogeneous ice nucleation mechanism.
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    22. 22
      Bi, Y.; Cabriolu, R.; Li, T. Heterogeneous Ice Nucleation Controlled by the Coupling of Surface Crystallinity and Surface Hydrophilicity. J. Phys. Chem. C 2016, 120, 1507– 1514,  DOI: 10.1021/acs.jpcc.5b09740
      22
      Heterogeneous Ice Nucleation Controlled by the Coupling of Surface Crystallinity and Surface Hydrophilicity
      Bi, Yuanfei; Cabriolu, Raffaela; Li, Tianshu
      Journal of Physical Chemistry C (2016), 120 (3), 1507-1514CODEN: JPCCCK; ISSN:1932-7447. (American Chemical Society)
      Here we show, by advanced mol. simulations, that the heterogeneous nucleation of ice on graphitic surface is controlled by the coupling of surface crystallinity and surface hydrophilicity. Mol. level anal. reveals that the cryst. graphitic lattice with an appropriate hydrophilicity may indeed template ice basal plane by forming a strained ice layer, thus significantly enhancing its ice nucleation efficiency. Remarkably, the templating effect is found to transit from within the first contact layer of water to the second as the hydrophilicity increases, yielding an oscillating distinction between the cryst. and amorphous graphitic surfaces in their ice nucleation efficiencies. Our study sheds new light on the long-standing question of what constitutes a good ice nucleator.
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    23. 23
      Zheng, Y.; Su, C.; Lu, J.; Loh, K. P. Room-Temperature Ice Growth on Graphite Seeded by Nano-Graphene Oxide. Angew. Chem., Int. Ed. 2013, 52, 8708– 8712,  DOI: 10.1002/anie.201302608
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      Room-Temperature Ice Growth on Graphite Seeded by Nano-Graphene Oxide
      Zheng, Yi; Su, Chenliang; Lu, Jiong; Loh, Kian Ping
      Angewandte Chemie, International Edition (2013), 52 (33), 8708-8712CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)
      The Stenocara beetle in the Namib Desert collects drinking droplets from the morning mist using its waxy wings, which are tailored with sub-millimeter hydrophilic humps. Superhydrophilic graphene oxide nanoflakes are biomimetic analogs of these humps and can seed ice nucleation on hydrophobic graphite. Various ice solids can thus be grown at ambient conditions.
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    24. 24
      Steiner, T. The Hydrogen Bond in the Solid State. Angew. Chem., Int. Ed. 2002, 41, 48– 76,  DOI: 10.1002/1521-3773(20020104)41:1<48::aid-anie48>3.0.co;2-u
      24
      Reviews: The hydrogen bond in the solid state
      Steiner, Thomas
      Angewandte Chemie, International Edition (2002), 41 (1), 48-76CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH)
      A review. The hydrogen bond is the most important of all directional intermol. interactions. It is operative in detg. mol. conformation, mol. aggregation, and the function of a vast no. of chem. systems ranging from inorg. to biol. Research into hydrogen bonds experienced a stagnant period in the 1980s but re-opened around 1990, and has been in rapid development since then. In terms of modern concepts, the hydrogen bond is understood as a very broad phenomenon, and it is accepted that there are open borders to other effects. There are dozens of different types of X-H···A hydrogen bonds that occur commonly in the condensed phases, and in addn. there are innumerable less common ones. Dissocn. energies span more than two orders of magnitude (about 02.-40 kcal mol-1). Within this range, the nature of the interaction is not const., but its electrostatic, covalent, and dispersion contributions vary in their relative wts. The hydrogen bond has broad transition regions that merge continuously with the covalent bond, the van der Waals interaction, the ionic interaction, and also the cation-π interaction. All hydrogen bonds can be considered as incipient proton transfer reactions, and for strong hydrogen bonds, this reaction can be in a very advanced state. In this review, a coherent survey is given on all these matters.
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    25. 25
      Whale, T. F.; Rosillo-Lopez, M.; Murray, B. J.; Salzmann, C. G. Ice Nucleation Properties of Oxidized Carbon Nanomaterials. J. Phys. Chem. Lett. 2015, 6, 3012– 3016,  DOI: 10.1021/acs.jpclett.5b01096
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      Ice Nucleation Properties of Oxidized Carbon Nanomaterials
      Whale, Thomas F.; Rosillo-Lopez, Martin; Murray, Benjamin J.; Salzmann, Christoph G.
      Journal of Physical Chemistry Letters (2015), 6 (15), 3012-3016CODEN: JPCLCD; ISSN:1948-7185. (American Chemical Society)
      Heterogeneous ice nucleation is an important process in many fields, particularly atm. science, but is still poorly understood. All known inorg. ice nucleating particles are relatively large in size and tend to be hydrophilic. Hence it is not obvious that carbon nanomaterials should nucleate ice. However, in this paper we show that four different readily water-dispersible carbon nanomaterials are capable of nucleating ice. The tested materials were carboxylated graphene nanoflakes, graphene oxide, oxidized single walled carbon nanotubes and oxidized multiwalled carbon nanotubes. The carboxylated graphene nanoflakes have a diam. of ∼30 nm and are among the smallest entities obsd. so far to nucleate ice. Overall, carbon nanotubes were found to nucleate ice more efficiently than flat graphene species, and less oxidized materials nucleated ice more efficiently than more oxidized species. These well-defined carbon nanomaterials may pave the way to bridging the gap between exptl. and computational studies of ice nucleation.
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    26. 26
      Lupi, L.; Hudait, A.; Molinero, V. Heterogeneous Nucleation of Ice on Carbon Surfaces. J. Am. Chem. Soc. 2014, 136, 3156– 3164,  DOI: 10.1021/ja411507a
      26
      Heterogeneous Nucleation of Ice on Carbon Surfaces
      Lupi, Laura; Hudait, Arpa; Molinero, Valeria
      Journal of the American Chemical Society (2014), 136 (8), 3156-3164CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
      Atm. aerosols can promote the heterogeneous nucleation of ice, impacting the radiative properties of clouds and Earth's climate. The exptl. study of heterogeneous freezing of water droplets by carbonaceous particles reveals widespread ice freezing temps. It is not known which structural and chem. characteristics of soot account for the variability in ice nucleation efficiency. Here the authors use mol. dynamics simulations to study the nucleation of ice from liq. water in contact with graphitic surfaces. Atomically flat carbon surfaces promote heterogeneous nucleation of ice, while molecularly rough surfaces with the same hydrophobicity do not. Graphitic surfaces and other surfaces that promote ice nucleation induce layering in the interfacial water, suggesting that the order imposed by the surface on liq. water may play an important role in the heterogeneous nucleation mechanism. The authors study a large set of graphitic surfaces of various dimensions and radii of curvature and find that variations in nanostructures alone could account for the spread in the freezing temps. of ice on soot in expts. A characterization of the nanostructure of soot is needed to predict its ice nucleation efficiency.
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    27. 27
      Biggs, C. I.; Packer, C.; Hindmarsh, S.; Walker, M.; Wilson, N. R.; Rourke, J. P.; Gibson, M. I. Impact of Sequential Surface-Modification of Graphene Oxide on Ice Nucleation. Phys. Chem. Chem. Phys. 2017, 19, 21929– 21932,  DOI: 10.1039/c7cp03219f
      27
      Impact of sequential surface-modification of graphene oxide on ice nucleation
      Biggs, Caroline I.; Packer, Christopher; Hindmarsh, Steven; Walker, Marc; Wilson, Neil R.; Rourke, Jonathan P.; Gibson, Matthew I.
      Physical Chemistry Chemical Physics (2017), 19 (33), 21929-21932CODEN: PPCPFQ; ISSN:1463-9076. (Royal Society of Chemistry)
      Base-washed graphene-oxide which has been sequentially-modified by thiol-epoxy chem., results in materials with ice-nucleation activity. The role of hydrophilic and hydrophobic grafts and polymers was evaluated with the most potent functioning at just 0.25 wt.%. These 2D hybrid materials may find use in cryopreservation and fundamental studies on ice formation.
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    28. 28
      Behera, S. N.; Sharma, M. Investigating the Potential Role of Ammonia in Ion Chemistry of Fine Particulate Matter Formation for an Urban Environment. Sci. Total Environ. 2010, 408, 3569– 3575,  DOI: 10.1016/j.scitotenv.2010.04.017
      28
      Investigating the potential role of ammonia in ion chemistry of fine particulate matter formation for an urban environment
      Behera, Sailesh N.; Sharma, Mukesh
      Science of the Total Environment (2010), 408 (17), 3569-3575CODEN: STENDL; ISSN:0048-9697. (Elsevier B.V.)
      To assess the potential role of NH3 in ion chem. of PM2.5 aerosols, measurements of PM2.5 (particulate matter with aerodynamic diam. <2.5 μm) along with its ionic speciation and gaseous pollutants (SO2, NOx, NH3, HNO3) were made in summer and winter, 2007-2008, at 4 sample sites in Kanpur, an urban-industrial city in the Ganga Basin, India. Mean concns. of water-sol. ions were obsd. in the following order: summer: SO42-, 26.3 μg/m3 > NO3-, 16.8 μg/m3 > NH4+, 15.1 μg/m3 > Ca2+, 4.1 μg/m3 > Na+, 2.4 μg/m3 > K+, 2.1 μg/m3; and winter: SO42-, 28.9 μg/m3 > NO3-, 23.0 μg/m3 > NH4+, 16.4 μg/m3 > Ca2+, 3.4 μg/m3 > K+, 3.3 μg/m3 > Na+, 3.2 μg/m3. The mean molar NH4+:SO42- molar ratio, 2.8 ± 0.6 (mostly >2), indicated the abundance of NH3 to neutralize H2SO4. Excess NH4+ was inferred to be assocd. with NO3- and Cl-. A higher S (Fs, 58%) vs. N conversion ratios (Fn: 39%) indicated SO42- were the preferred secondary species to NO3-. The charge balance for the PM2.5 ion chem. showed that compds. formed from an NH3 precursor were (NH4)2SO4, NH4NO3, and NH4Cl. Results conclusively established that while there are higher contributions of NH4+ and SO42- to PM2.5 in summer, particulate NO3- have higher winter contributions, crit. due to low temp.-driven reactions between NH3 and HNO3 in a forward direction for enhanced NO3- formation. Inorg. secondary aerosol formation accounted for 30% of the PM2.5 mass; thus, any particulate control strategy should include optimal control of primary precursor gases including NH3.
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    29. 29
      Pandolfi, M.; Amato, F.; Reche, C.; Alastuey, A.; Otjes, R. P.; Blom, M. J.; Querol, X. Summer Ammonia Measurements in a Densely Populated Mediterranean City. Atmos. Chem. Phys. 2012, 12, 7557– 7575,  DOI: 10.5194/acp-12-7557-2012
      29
      Summer ammonia measurements in a densely populated Mediterranean city
      Pandolfi, M.; Amato, F.; Reche, C.; Alastuey, A.; Otjes, R. P.; Blom, M. J.; Querol, X.
      Atmospheric Chemistry and Physics (2012), 12 (16), 7557-7575CODEN: ACPTCE; ISSN:1680-7316. (Copernicus Publications)
      Real-time measurements of ambient concns. of gas-phase ammonia (NH3) were performed in Barcelona (NE Spain) in summer between May and Sept. 2011. Two measurement sites were selected: one in an urban background traffic-influenced area (UB) and the other in the historical city center (CC). Levels of NH3 were higher at CC (5.6 ± 2.1 μg m-3 or 7.5 ± 2.8 ppbv) compared with UB (2.2 ± 1.0 μg m-3 or 2.9 ± 1.3 ppbv). This difference is attributed to the contribution from non-traffic sources such as waste containers, sewage systems, humans and open markets more dense in the densely populated historical city center. Under high temps. in summer these sources had the potential to increase the ambient levels of NH3 well above the urban-background-traffic-influenced UB measurement station. Measurements were used to assess major local emissions, sinks and diurnal evolution of NH3. The measured levels of NH3, esp. high in the old city, may contribute to the high mean annual concns. of secondary sulfate and nitrate measured in Barcelona compared with other cities in Spain affected by high traffic intensity. Ancillary measurements, including PM10, PM2.5, PM1 levels (Particulate Matter with aerodynamic diam. smaller than 10 μm, 2.5 μm, and 1 μm), gases and black carbon concns. and meteorol. data, were performed during the measurement campaign. The anal. of specific periods (3 special cases) during the campaign revealed that road traffic was a significant source of NH3. However, its effect was more evident at UB compared with CC where it was masked given the high levels of NH3 from non-traffic sources measured in the old city. The relationship between SO2-4 daily concns. and gas-fraction ammonia (NH3/(NH3 + NH+4)) revealed that the gas-to-particle phase partitioning (volatilization or ammonium salts formation) also played an important role in the evolution of NH3 concn. in summer in Barcelona.
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    30. 30
      Phan, N.-T.; Kim, K.-H.; Shon, Z.-H.; Jeon, E.-C.; Jung, K.; Kim, N.-J. Analysis of Ammonia Variation in the Urban Atmosphere. Atmos. Environ. 2013, 65, 177– 185,  DOI: 10.1016/j.atmosenv.2012.10.049
      30
      Analysis of ammonia variation in the urban atmosphere
      Phan, Nhu-Thuc; Kim, Ki-Hyun; Shon, Zang-Ho; Jeon, Eui-Chan; Jung, Kweon; Kim, Nam-Jin
      Atmospheric Environment (2013), 65 (), 177-185CODEN: AENVEQ; ISSN:1352-2310. (Elsevier Ltd.)
      Long-term monitoring of NH3 concn. and other trace gases was made at hourly intervals along with meteorol. parameters in Seoul, Korea for a 1-yr period (1 Sept. 2010-23 August 2011). The mean NH3 concns. measured at 2 sites (Gwang-Jin (GJ) and Gang-Seo (GS) districts) were 10.9 ± 4.25 and 12.3 ± 4.23 ppb, resp. A comparison of the seasonal data shows its relative dominance at both GJ and GS sites during the warm period (summer and spring) over the cool period (winter and fall). Likewise, over the diurnal scale, relative dominance during daytime was also apparent (p < 0.05). A comparison between different studies suggests that the long-term trend of NH3 levels should be tightly affected by an increasing no. of vehicles. As such, the results of the statistical anal. also point to the potentially significant role of traffic activities in the elevation of NH3 levels in urban areas.
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    31. 31
      Hauptmann, A.; Handle, K. F.; Baloh, P.; Grothe, H.; Loerting, T. Does the Emulsification Procedure Influence Freezing and Thawing of Aqueous Droplets?. J. Chem. Phys. 2016, 145, 211923,  DOI: 10.1063/1.4965434
      There is no corresponding record for this reference.
    32. 32
      Pummer, B. G.; Bauer, H.; Bernardi, J.; Bleicher, S.; Grothe, H. Suspendable Macromolecules Are Responsible for Ice Nucleation Activity of Birch and Conifer Pollen. Atmos. Chem. Phys. 2012, 12, 2541– 2550,  DOI: 10.5194/acp-12-2541-2012
      32
      Suspendable macromolecules are responsible for ice nucleation activity of birch and conifer pollen
      Pummer, B. G.; Bauer, H.; Bernardi, J.; Bleicher, S.; Grothe, H.
      Atmospheric Chemistry and Physics (2012), 12 (5), 2541-2550CODEN: ACPTCE; ISSN:1680-7316. (Copernicus Publications)
      The ice nucleation of bioaerosols (bacteria, pollen, spores, etc.) is a topic of growing interest, since their impact on ice cloud formation and thus on radiative forcing, an important parameter in global climate, is not yet fully understood. Here we show that pollen of different species strongly differ in their ice nucleation behavior. The av. freezing temps. in lab. expts. range from 240 to 255 K. As the most efficient nuclei (silver birch, Scots pine and common juniper pollen) have a distribution area up to the Northern timberline, their ice nucleation activity might be a cryoprotective mechanism. Far more intriguingly, it has turned out that water, which has been in contact with pollen and then been sepd. from the bodies, nucleates as good as the pollen grains themselves. The ice nuclei have to be easily-suspendable macromols. located on the pollen. Once extd., they can be distributed further through the atm. than the heavy pollen grains and so presumably augment the impact of pollen on ice cloud formation even in the upper troposphere. Our expts. lead to the conclusion that pollen ice nuclei, in contrast to bacterial and fungal ice nucleating proteins, are non-proteinaceous compds.
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    33. 33
      Zolles, T.; Burkart, J.; Häusler, T.; Pummer, B.; Hitzenberger, R.; Grothe, H. Identification of Ice Nucleation Active Sites on Feldspar Dust Particles. J. Phys. Chem. A 2015, 119, 2692– 2700,  DOI: 10.1021/jp509839x
      33
      Identification of ice nucleation active sites on feldspar dust particles
      Zolles, Tobias; Burkart, Julia; Haeusler, Thomas; Pummer, Bernhard; Hitzenberger, Regina; Grothe, Hinrich
      Journal of Physical Chemistry A (2015), 119 (11), 2692-2700CODEN: JPCAFH; ISSN:1089-5639. (American Chemical Society)
      Mineral dusts originating from Earth's crust are known to be important atm. ice nuclei. In agreement with earlier studies, feldspar was found as the most active of the tested natural mineral dusts. Here we investigated in closer detail the reasons for its activity and the difference in the activity of the different feldspars. Conclusions are drawn from SEM, X-ray powder diffraction, IR spectroscopy, and oil-immersion freezing expts. K-feldspar showed by far the highest ice nucleation activity. Finally, we give a potential explanation of this effect, finding alkali-metal ions having different hydration shells and thus an influence on the ice nucleation activity of feldspar surfaces.
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    34. 34
      Johnson, D. W.; Dobson, B. P.; Coleman, K. S. A Manufacturing Perspective on Graphene Dispersions. Curr. Opin. Colloid Interface Sci. 2015, 20, 367– 382,  DOI: 10.1016/j.cocis.2015.11.004
      34
      A manufacturing perspective on graphene dispersions
      Johnson, David W.; Dobson, Ben P.; Coleman, Karl S.
      Current Opinion in Colloid & Interface Science (2015), 20 (5-6), 367-382CODEN: COCSFL; ISSN:1359-0294. (Elsevier Ltd.)
      Harnessing the exceptional phys. properties of graphene often requires its dispersion into aq. or org. media. Dispersion must be achieved at a concn. and stability appropriate to the final application. However, the strong interaction between graphene sheets means it disperses poorly in all but a few high boiling org. solvents. This review presents an overview of graphene dispersion applications and a discussion of dispersion strategies: in particular the effect of shear, solvent and chem. modification on the dispersion of graphene (including graphene oxide and reduced graphene oxide). These techniques are discussed in the context of manufg. and commercialization.
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    35. 35
      Konios, D.; Stylianakis, M. M.; Stratakis, E.; Kymakis, E. Dispersion Behaviour of Graphene Oxide and Reduced Graphene Oxide. J. Colloid Interface Sci. 2014, 430, 108– 112,  DOI: 10.1016/j.jcis.2014.05.033
      35
      Dispersion behaviour of graphene oxide and reduced graphene oxide
      Konios, Dimitrios; Stylianakis, Minas M.; Stratakis, Emmanuel; Kymakis, Emmanuel
      Journal of Colloid and Interface Science (2014), 430 (), 108-112CODEN: JCISA5; ISSN:0021-9797. (Elsevier B.V.)
      The dispersion behavior of graphene oxide (GO) and chem. reduced GO (rGO) has been investigated in a wide range of org. solvents. The effect of the redn. process on the GO soly. in eighteen different solvents was examd. and analyzed, taking into consideration the solvent polarity, the surface tension and the Hansen and Hildebrand soly. parameters. rGO concns. up to ∼9 μg/mL in chlorinated solvents were achieved, demonstrating an efficient solubilization strategy, extending the scope for scalable liq.-phase processing of conductive rGO inks for the development of printed flexible electronics.
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    36. 36
      Broadley, S. L.; Murray, B. J.; Herbert, R. J.; Atkinson, J. D.; Dobbie, S.; Malkin, T. L.; Condliffe, E.; Neve, L. Immersion Mode Heterogeneous Ice Nucleation by an Illite Rich Powder Representative of Atmospheric Mineral Dust. Atmos. Chem. Phys. 2012, 12, 287– 307,  DOI: 10.5194/acp-12-287-2012
      36
      Immersion mode heterogeneous ice nucleation by an illite rich powder representative of atmospheric mineral dust
      Broadley, S. L.; Murray, B. J.; Herbert, R. J.; Atkinson, J. D.; Dobbie, S.; Malkin, T. L.; Condliffe, E.; Neve, L.
      Atmospheric Chemistry and Physics (2012), 12 (1), 287-307CODEN: ACPTCE; ISSN:1680-7316. (Copernicus Publications)
      Atm. dust rich in illite is transported globally from arid regions and impacts cloud properties through the nucleation of ice. We present measurements of ice nucleation in water droplets contg. known quantities of an illite rich powder under atmospherically relevant conditions. The illite rich powder used here, NX illite, has a similar mineralogical compn. to atm. mineral dust sampled in remote locations, i.e. dust which has been subject to long range transport, cloud processing and sedimentation. Arizona Test Dust, which is used in other ice nucleation studies as a model atm. dust, has a significantly different mineralogical compn. and we suggest that NX illite is a better surrogate of natural atm. dust. Using optical microscopy, heterogeneous nucleation in the immersion mode by NX illite was obsd. to occur dominantly between 246 K and the homogeneous freezing limit. In general, higher freezing temps. were obsd. when larger surface areas of NX illite were present within the drops. Homogenous nucleation was obsd. to occur in droplets contg. low surface areas of NX illite. We show that NX illite exhibits strong particle to particle variability in terms of ice nucleating ability, with ∼1 in 105 particles dominating ice nucleation when high surface areas were present. In fact, this work suggests that the bulk of atm. mineral dust particles may be less efficient at nucleating ice than assumed in current model parameterisations. For droplets contg. ≤2 × 10-6 cm2 of NX illite, freezing temps. did not noticeably change when the cooling rate was varied by an order of magnitude. The data obtained during cooling expts. (surface area ≤2 × 10-6 cm2) is shown to be inconsistent with the single component stochastic model, but is well described by the singular model (ns(236.2 K ≤T ≤247.5 K) = exp(6.53043 × 104 - 8.2153088 × 102T + 3.446885376T2 - 4.822268 × 10-3T3). However, droplets continued to freeze when the temp. was held const., which is inconsistent with the time independent singular model. We show that this apparent discrepancy can be resolved using a multiple component stochastic model in which it is assumed that there are many types of nucleation sites, each with a unique temp. dependent nucleation coeff. Cooling rate independence can be achieved with this time dependent model if the nucleation rate coeffs. increase very rapidly with decreasing temp., thus reconciling our measurement of nucleation at const. temp. with the cooling rate independence.
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    37. 37
      Connolly, P. J.; Möhler, O.; Field, P. R.; Saathoff, H.; Burgess, R.; Choularton, T.; Gallagher, M. Studies of Heterogeneous Freezing by Three Different Desert Dust Samples. Atmos. Chem. Phys. 2009, 9, 2805– 2824,  DOI: 10.5194/acp-9-2805-2009
      37
      Studies of heterogeneous freezing by three different desert dust samples
      Connolly, P. J.; Mohler, O.; Field, P. R.; Saathoff, H.; Burgess, R.; Choularton, T.; Gallagher, M.
      Atmospheric Chemistry and Physics (2009), 9 (8), 2805-2824CODEN: ACPTCE; ISSN:1680-7316. (Copernicus Publications)
      We present results of expts. at the aerosol interactions and dynamics in the atm. (AIDA) chamber facility looking at the freezing of water by three different types of mineral particles at temps. between -12 and -33°C. The three different dusts are Asia Dust-1 (AD1), Sahara Dust-2 (SD2) and Arizona test Dust (ATD). The dust samples used had particle concns. of sizes that were log-normally distributed with mode diams. between 0.3 and 0.5 μm and std. deviations, σg, of 1.6-1.9. The results from the freezing expts. are consistent with the singular hypothesis of ice nucleation. The dusts showed different nucleation abilities, with ATD showing a rather sharp increase in ice-active surface site d. at temps. less than -24°C. AD1 was the next most efficient freezing nuclei and showed a more gradual increase in activity than the ATD sample. SD2 was the least active freezing nuclei. We used data taken with particle counting probes to derive the ice-active surface site d. forming on the dust as a function of temp. for each of the three samples and polynomial curves are fitted to this data. The curve fits are then used independently within a bin microphys. model to simulate the ice formation rates from the expts. in order to test the validity of parameterizing the data with smooth curves. Good agreement is found between the measurements and the model for AD1 and SD2; however, the curve for ATD does not yield results that agree well with the observations. The reason for this is that more expts. between -20 and -24°C are needed to quantify the rather sharp increase in ice-active surface site d. on ATD in this temp. regime. The curves presented can be used as parameterizations in atm. cloud models where cooling rates of approx. 1 °C min-1 or more are present to predict the concn. of ice crystals forming by the condensation-freezing mode of ice nucleation. Finally a polynomial is fitted to all three samples together in order to have a parameterization describing the av. ice-active surface site d. vs. temp. for an equal mixt. of the three dust samples.
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    38. 38
      DeMott, P. J. Quantitative Descriptions of Ice Formation Mechanisms of Silver Iodide-Type Aerosols. Atmos. Res. 1995, 38, 63– 99,  DOI: 10.1016/0169-8095(94)00088-u
      38
      Quantitative descriptions of ice formation mechanisms of silver iodide-type aerosols
      DeMott, P.J.
      Atmospheric Research (1995), 38 (1-4), 63-99CODEN: ATREEW; ISSN:0169-8095. (Elsevier)
      Lab. and numerical cloud model expts. were designed to obtain quant. data describing ice formation by two specific aerosols used operationally for cloud modification. Exptl. methodologies and a quant. framework for predicting ice formation by these silver iodide-based aerosols were based on four currently accepted nucleation mechanisms (modes) and their inherent dependencies on the varied temp., pressure, humidity, and cloud conditions that can be encountered in the atm. The processes considered were deposition, condensation freezing, contact freezing and immersion freezing nucleation. Particle size dependencies were also quantified. The Colorado State University dynamic (controlled expansion) cloud chamber was used to reproduce atm. cloud conditions exptl. An adiabatic cloud model was adapted for equiv. simulation of cloud chamber expts. Hydrophobic AgI-AgCl and hygroscopic AgI-AgCl-4NaCl aerosols were found to function by some combination of all four nucleation mechanisms. AgI-AgCl aerosols were found to be potentially most efficient as contact freezing nuclei, but slow collision rates between IN and cloud droplets permit deposition and condensation freezing nucleation to become important for many cloud conditions. Condensation freezing was seen to progressively dominate ice formation when AgI-AgCl aerosols were exposed to increasing supersatn. with respect to water in the typical atm. range (up to 1%). Immersion freezing nucleation was always less efficient than contact freezing. The hygroscopic AgI-AgCl-4NaCl aerosols displayed deposition and condensation freezing active site densities about one order of magnitude higher than the AgI-AgCl aerosols, while contact freezing activity was not discernable. Immersion freezing could be as important or more important than condensation freezing nucleation for these hygroscopic aerosols depending on cloud characteristics and how aerosols are released into cloud. Instantaneous exposure of either ice nucleus aerosol to high water supersaturations caused the dominance of the immersion freezing mechanism. Quant. results were formulated for use in numerical cloud modeling. Ice crystal formation subsequently predicted in cloud model simulations showed good agreement with ice formation measured in cloud chamber simulations of relevant cloud seeding methodologies.
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    39. 39
      Niedermeier, D.; Hartmann, S.; Shaw, R. A.; Covert, D.; Mentel, T. F.; Schneider, J.; Poulain, L.; Reitz, P.; Spindler, C.; Clauss, T. Heterogeneous Freezing of Droplets with Immersed Mineral Dust Particles—Measurements and Parameterization. Atmos. Chem. Phys. 2010, 10, 3601– 3614,  DOI: 10.5194/acp-10-3601-2010
      There is no corresponding record for this reference.
    40. 40
      Edwards, G. R.; Evans, L. F.; La Mer, V. K. Ice Nucleation by Monodisperse Silver Iodide Particles. J. Colloid Sci. 1962, 17, 749– 758,  DOI: 10.1016/0095-8522(62)90049-1
      40
      Ice nucleation by monodisperse silver iodide particles
      Edwards, G. R.; Evans, L. F.; La Mer, V. K.
      Journal of Colloid Science (1962), 17 (), 749-58CODEN: JCSCA7; ISSN:0095-8522.
      Ice nucleation was studied by using monodisperse AgI sols. prepd. by the decompn. of the complex formed by dissolving AgI in strong aq. solns. of KI. Microscopic observations were made of the temp. at which 50% of the droplets had frozen, and of the no. of AgI particles in contact with each droplet. The nucleation temp. depended on the no. of particles in contact with the drop, indicating that particles of one size and crystal form are not equally active as freezing nuclei, but that the frequency of occurrence of nucleating sites on a given particle is proportional to the surface area. It is proposed that the activity of various AgI prepns. should be quoted in terms of the probability that a given nucleation site should occur on a particle of given size.
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    41. 41
      Whale, T. F.; Murray, B. J.; O’Sullivan, D.; Wilson, T. W.; Umo, N. S.; Baustian, K. J.; Atkinson, J. D.; Workneh, D. A.; Morris, G. J. A Technique for Quantifying Heterogeneous Ice Nucleation in Microlitre Supercooled Water Droplets. Atmos. Meas. Tech. 2015, 8, 2437– 2447,  DOI: 10.5194/amt-8-2437-2015
      41
      A technique for quantifying heterogeneous ice nucleation in microlitre supercooled water droplets
      Whale, T. F.; Murray, B. J.; O'Sullivan, D.; Wilson, T. W.; Umo, N. S.; Baustian, K. J.; Atkinson, J. D.; Workneh, D. A.; Morris, G. J.
      Atmospheric Measurement Techniques (2015), 8 (6), 2437-2447CODEN: AMTTC2; ISSN:1867-8548. (Copernicus Publications)
      In many clouds, the formation of ice requires the presence of particles capable of nucleating ice. Ice-nucleating particles (INPs) are rare in comparison to cloud condensation nuclei. However, the fact that only a small fraction of aerosol particles can nucleate ice means that detection and quantification of INPs is challenging. This is particularly true at temps. above about -20 °C since the population of particles capable of serving as INPs decreases dramatically with increasing temp. In this paper, we describe an exptl. technique in which droplets of microlitre vol. contg. ice-nucleating material are cooled down at a controlled rate and their freezing temps. recorded. The advantage of using large droplet vols. is that the surface area per droplet is vastly larger than in expts. focused on single aerosol particles or cloud-sized droplets. This increases the probability of observing the effect of less common, but important, high-temp. INPs and therefore allows the quantification of their ice nucleation efficiency. The potential artifacts which could influence data from this expt., and other similar expts., are mitigated and discussed. Exptl. detd. heterogeneous ice nucleation efficiencies for K-feldspar (microcline), kaolinite, chlorite, NX-illite, Snomax and silver iodide are presented.
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    42. 42
      Sadezky, A.; Muckenhuber, H.; Grothe, H.; Niessner, R.; Pöschl, U. Raman Micro Spectroscopy of Soot and Related Carbonaceous Materials: Spectral Analysis and Structural Information. Carbon 2005, 43, 1731– 1742,  DOI: 10.1016/j.carbon.2005.02.018
      42
      Raman microspectroscopy of soot and related carbonaceous materials. Spectral analysis and structural information
      Sadezky, A.; Muckenhuber, H.; Grothe, H.; Niessner, R.; Poeschl, U.
      Carbon (2005), 43 (8), 1731-1742CODEN: CRBNAH; ISSN:0008-6223. (Elsevier Ltd.)
      Exptl. conditions and math. fitting procedures for the collection and anal. of Raman spectra of soot and related carbonaceous materials were investigated and optimized with a Raman microscope system operated at 3 different laser excitation wavelengths (514, 633, and 780 nm). Several band combinations for spectral anal. were tested, and a combination of 4 Lorentzian-shaped bands (G, D1, D2, D4) at about 1580, 1350, 1620, and 1200 cm-1, resp., with a Gaussian-shaped band (D3) at ∼1500 cm-1 was best suited for the 1st-order spectra. The 2nd-order spectra were best fitted with Lorentzian-shaped bands at about 2450, 2700, 2900, and 3100 cm-1. Spectral parameters (band positions, full widths at half max., and intensity ratios) are reported for several types of industrial C black (Degussa Printex, Cabot Monarch), diesel soot (particulate matter from modern heavy duty vehicle and passenger car engine exhaust, NIST SRM1650), spark-discharge soot (Palas GfG100), and graphite. Several parameters, in particular the width of the D1 band at ∼1350 cm-1, provide structural information and allow to discriminate the sample materials, but the characterization and distinction of different types of soot is limited by the exptl. reproducibility of the spectra and the statistical uncertainties of curve fitting. The results are discussed and compared with x-ray diffraction measurements and earlier Raman spectroscopic studies of comparable materials, where different measurement and fitting procedures was applied.
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      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD2MXltFGrtLc%253D&md5=045e6d9ee2eb3d84bd001fca25bc7f62
    43. 43
      Weast, C. R.; Astle, M. J. Crc Handbook of Chemistry; CRC Press: Boca Raton, FL, 1981.
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      Chakrabarti, M. H.; Low, C. T. J.; Brandon, N. P.; Yufit, V.; Hashim, M. A.; Irfan, M. F.; Akhtar, J.; Ruiz-Trejo, E.; Hussain, M. A. Progress in the Electrochemical Modification of Graphene-Based Materials and Their Applications. Electrochim. Acta 2013, 107, 425– 440,  DOI: 10.1016/j.electacta.2013.06.030
      44
      Progress in the electrochemical modification of graphene-based materials and their applications
      Chakrabarti, M. H.; Low, C. T. J.; Brandon, N. P.; Yufit, V.; Hashim, M. A.; Irfan, M. F.; Akhtar, J.; Ruiz-Trejo, E.; Hussain, M. A.
      Electrochimica Acta (2013), 107 (), 425-440CODEN: ELCAAV; ISSN:0013-4686. (Elsevier Ltd.)
      A review. Graphene is a 2D allotrope of carbon with exciting properties such as extremely high electronic cond. and superior mech. strength. It has considerable potential for applications in fields such as biosensors, electrochem. energy storage, and electronics. In most cases, graphene was functionalized and modified with other materials to prep. composites. This work reviews the electrochem. modification of graphene. Commencing with a brief history, a summary of several different means of modifying graphene to effect diverse applications is provided. This is followed by a discussion on different composite materials that were prepd. with reduced graphene oxide prior to moving onto a detailed consideration of six different methods of electrochem. modifying graphene to prep. composite materials. These methods involve cathodic redn. of graphene oxide, electrophoretic deposition, electrodeposition techniques, electrospinning, electrochem. doping, and electrochem. polymn. Finally a consideration on the applications of electrochem. modified graphene composite materials in various fields is presented prior to discussing some prospects in enhancing the electrochem. process to realize excellent and economic composite materials in bulk.
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      Gao, W.; Alemany, L. B.; Ci, L.; Ajayan, P. M. New Insights into the Structure and Reduction of Graphite Oxide. Nat. Chem. 2009, 1, 403– 408,  DOI: 10.1038/nchem.281
      45
      New insights into the structure and reduction of graphite oxide
      Gao, Wei; Alemany, Lawrence B.; Ci, Lijie; Ajayan, Pulickel M.
      Nature Chemistry (2009), 1 (5), 403-408, S403/1-S403/20CODEN: NCAHBB; ISSN:1755-4330. (Nature Publishing Group)
      Graphite oxide is one of the main precursors of graphene-based materials, which are highly promising for various technol. applications because of their unusual electronic properties. Although epoxy and hydroxyl groups are widely accepted as its main functionalities, the complete structure of graphite oxide has remained elusive. By interpreting spectroscopic data in the context of the major functional groups believed to be present in graphite oxide, we now show evidence for the presence of five- and six-membered-ring lactols. On the basis of this chem. compn., we devised a complete redn. process through chem. conversion by sodium borohydride and sulfuric acid treatment, followed by thermal annealing. Only small amts. of impurities are present in the final product (<0.5 wt% of sulfur and nitrogen, compared with ∼3 wt% with other chem. redns.). This method is particularly effective in the restoration of the π-conjugated structure, and leads to highly sol. and conductive graphene materials.
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      Shearer, C. J.; Slattery, A. D.; Stapleton, A. J.; Shapter, J. G.; Gibson, C. T. Accurate Thickness Measurement of Graphene. Nanotechnology 2016, 27, 125704,  DOI: 10.1088/0957-4484/27/12/125704
      46
      Accurate thickness measurement of graphene
      Shearer, Cameron J.; Slattery, Ashley D.; Stapleton, Andrew J.; Shapter, Joseph G.; Gibson, Christopher T.
      Nanotechnology (2016), 27 (12), 125704/1-125704/10CODEN: NNOTER; ISSN:1361-6528. (IOP Publishing Ltd.)
      Graphene has emerged as a material with a vast variety of applications. The electronic, optical and mech. properties of graphene are strongly influenced by the no. of layers present in a sample. As a result, the dimensional characterization of graphene films is crucial, esp. with the continued development of new synthesis methods and applications. A no. of techniques exist to det. the thickness of graphene films including optical contrast, Raman scattering and scanning probe microscopy techniques. Atomic force microscopy (AFM), in particular, is used extensively since it provides three-dimensional images that enable the measurement of the lateral dimensions of graphene films as well as the thickness, and by extension the no. of layers present. However, in the literature AFM has proven to be inaccurate with a wide range of measured values for single layer graphene thickness reported (between 0.4 and 1.7 nm). This discrepancy has been attributed to tip-surface interactions, image feedback settings and surface chem. In this work, we use std. and carbon nanotube modified AFM probes and a relatively new AFM imaging mode known as PeakForce tapping mode to establish a protocol that will allow users to accurately det. the thickness of graphene films. In particular, the error in measuring the first layer is reduced from 0.1-1.3 nm to 0.1-0.3 nm. Furthermore, in the process we establish that the graphene-substrate adsorbate layer and imaging force, in particular the pressure the tip exerts on the surface, are crucial components in the accurate measurement of graphene using AFM. These findings can be applied to other 2D materials.
      >> More from SciFinder ®
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      Watanabe, M.; Makino, T.; Okada, K.; Kara, M.; Watabe, S.; Arai, S. Alkylbenzyldimethylammonium Salts as Inhibitors for the Ice Nucleating Activity of Erwinia-Ananas. Agric. Biol. Chem. 1988, 52, 201– 206,  DOI: 10.1271/bbb1961.52.201
      48
      Alkylbenzyldimethylammonium salts as inhibitors for the ice nucleating activity of Erwinia ananas
      Watanabe, Michiko; Makino, Takahiro; Okada, Katsuhide; Hara, Morio; Watabe, Satoshi; Arai, Soichi
      Agricultural and Biological Chemistry (1988), 52 (1), 201-6CODEN: ABCHA6; ISSN:0002-1369.
      A variety of chem. compds. were examd. as to their abilities to inhibit the ice nucleating activity of E. ananas IN-10 cells and their outer membrane fraction. The nucleating activity of the outer membrane fraction was inhibited by many surface-active species among the compds. examd., whereas that of cells was inhibited only the amines and ammonium salts having amphiphilic structures. Ammonium salts with both an alkyl group have a carbon no. of >8 and a benzyl group were particularly effective in inhibiting the nucleating activity of the bacterial cells. The inhibitory ability of one of the amphiphilic ammonium salts was greater at 15° than at 4°. When a tea plant was sprayed with one of the effective ammonium salts prior to being kept at -3° overnight, it was possible to protect the plant from freeze-injury at the minimal concn. of 250 ppm.
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      Zachariassen, K. E.; Kristiansen, E. Ice Nucleation and Antinucleation in Nature. Cryobiology 2000, 41, 257– 279,  DOI: 10.1006/cryo.2000.2289
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      Ice Nucleation and Antinucleation in Nature
      Zachariassen, Karl Erik; Kristiansen, Erlend
      Cryobiology (2000), 41 (4), 257-279CODEN: CRYBAS; ISSN:0011-2240. (Academic Press)
      A review with 117 refs. Plants and ectothermic animals use a variety of substances and mechanisms to survive exposure to subfreezing temps. Proteinaceous ice nucleators trigger freezing at high subzero temps., either to provide cold protection from released heat of fusion or to establish a protective extracellular freezing in freeze-tolerant species. Freeze-avoiding species increase their supercooling potential by removing ice nucleators and accumulating polyols. Terrestrial invertebrates and polar marine fish stabilize their supercooled state by means of noncolligatively acting antifreeze proteins. Some organisms also depress their body fluid m.p. to ambient temp. by evapn. and/or solute accumulation. (c) 2000 Academic Press.
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    • Synthesis and characterization of functionalized graphene samples (G-NPr3+X–); visual comparison of graphene and graphene oxide suspensions after sonication and after settling for 30 min; refreezing experiments of G-non; and XPS-determined C 1s components of all samples (PDF)


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