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Features of the benzene adsorption in polyfluoroalkyl layers of different structures grafted on surfaces of silica gel (SG) are studied using gas chromatography, static adsorption, and diffuse reflectance IR spectroscopy. After modification, Henry’s law constants determined from the gas chromatography data and the static benzene adsorption values fall in the order SG > SG–F(III) > SG–F > SG–iso-F(III), where samples SG–F(III), SG–F, and SG–iso-F(III) are produced using silanes n‑C6F13(CH2)2SiCl3, n‑C6F13(CH2)2Si(CH3)2Cl, and iso-C3F7(CH2)2SiCl3, respectively. It is found that the energy characteristics of adsorption of benzene and other hydrocarbons on the SG–F(III) sample with the linear trifunctional modifier are 3–7 kJ/mol higher than the respective characteristics determined on the initial support. The contact angles for nanoporous silica gels with polyfluoroalkyl layers are calculated from desorption data in the region of the capillary condensation hysteresis of the benzene adsorption isotherms.

The results from studying the physicochemical characteristics of the adsorption of n-alkanes, arenes, and acetonitrile on silicas of different origins, silica gels, and silochromes are presented. It is shown that increasing the concentration of silanol groups reduces the role of dispersion interactions accompanied by the intensification of specific interactions on silica gels, compared to silochromes. According to diffuse reflectance FTIR spectroscopy data, the acidity of silanol groups on silica gel is in this case less pronounced.

This is a comprehensive study of the physicochemical characterization of multicomponent aerosols in the smoky atmosphere of Moscow during the extreme wildfires of August 2010 and against the background atmosphere of August 2011. Thermal–optical analysis, liquid and ion chromatography, IR spectroscopy, and electron microscopy were used to determine the organic content (OC) and elemental content (EC) of carbon, organic/inorganic and ionic compounds, and biomass burning markers (anhydrosaccharides and the potassium ion) and study the morphology and elemental composition of individual particles. It has been shown that the fires are characterized by an increased OC/EC ratio and high concentrations of ammonium, potassium, and sulfate ions in correlation with an increased content of levoglucosan as a marker of biomass burning. The organic compounds containing carbonyl groups point to the process of photochemical aging and the formation of secondary organic aerosols in the urban atmosphere when aerosols are emitted from forest fires. A cluster analysis of individual particles has indicated that when the smokiest atmosphere is characterized by prevailing soot/tar ball particles, which are smoke-emission micromarkers.

Surface properties of silica gels modified by trifunctional polyfluorosilanes n-C6F13(CH2)2SiCl3 and iso-C3F7(CH2)2SiCl3 are studied using the methods of adsorption and gas chromatography with respect to nitrogen, hydrocarbon, and water molecules. It is shown that the branched structure of the grafted group and high concentration of grafted groups (2.7 nm–2) provide better screening of both residual silanols of the support and of additional hydroxyl groups formed in the course of synthesis as a result of hydrolysis. Comparison with the properties of silica gel with grafted monofunctional silane n-C6F13(CH2)2Si(CH3)2Cl shows that, in the case of an overall decrease in the adsorption values and considerable surface lyophobization, modification by trifunctional silanes irrespective of the modifier chain length allows obtaining adsorbents containing more polar centers than those in silica gel due to the possible participation in adsorption of additional silanols and a polar fragment of the grafted chain of–CH2–CF2–. A considerable difference in the course of isotherms of nitrogen and hexane adsorption–desorption is found in the range of capillary condensation hysteresis related to liophobicity of polyfluoroalkyl layers, a significant decrease in the pore wetting and the corresponding increase in wetting angle θ by hexane. Adsorption of water on fluorinated silicas is negligible and capillary condensation is not observed due to nonwettability of the pore surface by liquid adsorbate (θ > 90°).

Interaction between vapors of organic compounds and water with surfaces of mesoporous silica SBA-15 and silica SBA-15 modified with n-C6F13(CH2)2Si(CH3)2Cl via adsorption under static conditions is studied by means of gas chromatography and IR diffuse reflectance spectroscopy. It is shown that modification notably reduces the energy of disperse and specific interactions, along with the acidity of adsorption centers. Even low concentrations of the grafted groups (0.76 nm–2) allows us to obtain highly hydrophobic coatings on SBA-15 surfaces.

Using the static method and gas chromatography, the adsorption of nitrogen and hydrocarbons by SBA-15 silicas and commercially available silica gel (SG), as well as changes in the surface properties of these samples as a result of chemical modification with multifunctional perfluorohexylsilane ClSi(CH3)2(CH2)2(n-C6F13), are studied. The main factor that causes the high values of thermodynamic characteristics of adsorption on SBA-15 and its modified form is a relatively small pore size. The differences in the polarities of the samples testify to a high concentration of silanol groups on the initial and modified SG.

Lyophobized silicas containing relatively small numbers of grafted perfluorohexyl (1.1 nm−2) and perfluorobutyl (1.7 nm−2) groups are studied by means of gas chromatography, adsorption under static conditions, and IR spectroscopy. The results are compared to those obtained by us previously for a series of samples with dense polyfluoroalkyl monolayers (≥2.0 nm−2). Effects related to the influence of the grafting density and the size of fluorine-containing groups on the adsorption of polar compounds and the hydrophobicity of the surface are discussed.

The role of the grafting density of monofunctional polyfluoroalkylsilanes of the C n F2n − 1(CH2) m Si(CH3)2Cl general formula (where n = 3, 4, and 6; and m = 2 and 3) and their composition in intermolecular interactions of the molecules of saturated and aromatic hydrocarbons with a surface of chemically modified silica is studied by means of IR spectroscopy and adsorption-static and gas chromatography. It is shown that the higher the concentration and the shorter the length of the grafted chain, the greater (by a factor of 2 to 25) the drop in the adsorption values of hydrocarbons as a result of modifications, due to an increase in the degree of oleophobization of surface upon the formation of polyorganofluorine coatings. The high specificity of the surface with respect to benzene, which is due to the active participation of the polar fragment of a grafted chain in adsorption process, is related to the features of a relatively low-density sample with a concentration of grafted perfluorobutyl groups of 1.7 nm−2. It is shown that the thermodestruction of polyfluoroalkyl silica remains virtually unobserved upon heating to 523 K in an argon flow.

The influence of the modification of silica by octyltrichlorosilane with the formation of an oligomeric grafted layer (sample C8(II)) and additional silanization (sample C8(III)) on the thermodynamic adsorption characteristics (TACs) of different classes of organic compounds was investigated by gas chromatography. It was shown that the modification leads to decreased adsorption values for most of the investigated compounds (with the exception of alkanes, for which TACs on sample C8(II) approach the values observed on the initial support, due probably to additional interactions with silanol groups formed in modifying the surface with octyltrichlorosilane). It was established that blocking these silanol groups during additional silanization with trimethylsilane resulted in inert surfaces whose adsorption properties with respect to many compounds (including some capable of participating in strong specific interactions) approaches to the properties of octyl-silica with a close-packed grafted monolayer.

A number of samples that simulate the chemical composition of carbonaceous aerosols emitted by transport into the atmosphere have been synthesized using the method of deposition of organic compounds and sulfuric acid, which are identified in the particulate coverage of diesel and aircraft engine soot particles, onto the surface of elemental carbon. The analysis of water adsorption isotherms allows one to estimate the influence of the surface chemistry of particles on the degree of their hygroscopicity. Water adsorption measurements show that modification of a particle surface by nonpolar organics (aliphatic and aromatic hydrocarbons) leads to the hydrophobization of a soot surface. The impact of polar oxygen-containing organic compounds (ethers, ketones, aromatic, and aliphatic acids) on adsorption capacity with respect to the water of samples that they modify substantially depends on the nature and composition of the hydrophobic part of the molecules. Among the ionic compounds organic acid salts have the most hydrophilization effect, which is comparable with the adsorption capacity of soot with sulfuric acid deposited on its surface. This observation allows one to quantitatively define how the nature of chemical compounds on soot surface influences water adsorption and to estimate the interaction of water molecules with fossil fuel combustion particles in a humid atmosphere.

The protective properties of lyophobic layers of various natures chemically grafted to a silica carrier were comparatively studied. The modifiers were silanes with the compositions CF3(CH2)2Si(CH3)2Cl (CF3), C8H17Si(CH3)2Cl (C8H17), and ClSi(CH3)2[OSi(CH3)2]2Cl (OMS). The differences between the surface properties of chemically modified silicas observed in adsorption, chromatographic, and IR spectroscopic measurements were shown to be related to a nonuniform electron density distribution in CF3 grafted radicals and the special features of the structure of CF3 and OMS grafted layers caused by the possibility of interaction between the terminal groups of these radicals and the surface of the carrier. Modified silicas possessed low surface energy and were superhydrophobic materials. The sample with grafted octyl groups C8H17 had the highest stability with respect to water.

By means of the gas chromatography and a static adsorption method, the extent of fluorination of the carrier surface, determined by the length of the grafted radical chain, affects the adsorption properties of silicas with perfluorohexyl, perfluoropropyl, and trifluoromethyl coatings. The analysis of data on the original carrier and chemically hydrophobized silicas, including a sample with grafted octyl groups used as the reference, shows that modification leads to the decrease in both the adsorption (a at 298 K and the Henry constants (K H ) in a wide temperature range for hexane and benzene. However, in contrast to silicas with perfluoropropyl or perfluorohexyl coatings, the a and K H values on trifluorometylsilica became equal (n-alkanes) or even somewhat lower (aromatic hydrocarbons) than those observed on the non-polar octylsilica surface. Irrespective of the degree of fluorination of the silica surface, the substitution and screening of silanol groups in silica lead to weakening the polarity of polyfluoroalkylsilicas as compared with the original carrier.

The effect of the functionality of modifiers on the adsorption of vapors of compounds capable of strong specific interactions, including water, diethyl ether, and acetonitrile, on silicas with chemically grafted perfluorohexylsilanes (RSi(CH3)3 −m Cl m , where m (functionality) is 1, 2, 3 and R is polyfluoroalkyl) was studied by adsorption under static conditions, gas chromatography, and IR spectroscopy. It was found that modification with monofunctional silane results in the most hydrophobic coating and a comparatively low-polarity surface with a strongly decreased contribution of specific interactions compared with other modifiers.

The chemistry of the surface and structural and adsorption properties of fluorinated carbon fiber were studied by IR spectroscopy, gas chromatography, and static adsorption of vapors and dyes from aqueous solutions. Also, the quantitative characteristics of the influence of a binder (polytetrafluoroethylene) used to prepare a granulated adsorbent on the basis of the fiber were determined. The functional properties of the adsorbent were found to be largely determined by the properties of the initial fluorocarbon fiber. Fluorocarbons were shown to possess a developed porous structure and highly hydrophobic chemically homogeneous nonpolar surface for the adsorption of most of the organic compounds studied.

Regardless of the nature of the modifier (mono-, bi-, and trichlorosilanes with perfluorohexyl groups or monochlorooctylsilane), the modification of silica decreased retention volumes and adsorption values of both n-alkanes and aromatic hydrocarbons. The entropy factor can play a key role in adsorption intermolecular interactions on the surface of chemically modified silicas. The modification of the surface with bi- and trichloroperfluorohexylsilanes caused the appearance of new centers more active compared with those of the initial carrier. The most oleophobic and nonpolar coatings were obtained using monochlorosilane with perfluorohexyl groups as a modifier.

Porous silica-based pyrocarbon adsorbents were studied using adsorption, gas and liquid chromatography. A more uniform deposition of pyrolysis products on the surface was observed at low benzene conversion rates, at pyrolysis temperatures below 850°C and when a more heat-resistant macroporous silica with pore diameter, d > 300 A was used as the support. Gas chromatography and adsorption studies have shown that silica modified with pyrocarbon has similar chromatographic properties to acetylene and thermal carbon blacks, but is less homogeneous both geometrically and chemically. The high affinity of carbosilica gel for polyaromatic hydrocarbons and its high sensitivity to the geometric (steric) structure of such molecules in liquid chromatography are described.

The particles of soot, formed in the combustion chamber of a jet engine under conditions typical of a cruising power mode, are capable of adsorbing a considerable amount of water vapor owing to their microcrystalline structure, microporosity, and chemically heterogeneous surface.