Adsorption of Dihydrogen on Mesoporous Materials at 77 K

The adsorption of dihydrogen at 77 K is studied on a series of oxide materials including silica, pure titania and alumina, and mixed oxides. The experimental data obtained suggest that the sorption properties per unit area of mesopore surface depend on both the texture and chemical composition of the sample. A comparative procedure for the analysis of dihydrogen adsorption isotherms is considered.__________Translated from Kinetika i Kataliz, Vol. 46, No. 4, 2005, pp. 642–647.Original Russian Text Copyright © 2005 by Gavrilov.     

Structure and Adsorption Properties of Nanocrystalline Silicon

The structure of the particles of nanocrystalline silicon synthesized in argon plasma with added oxygen is studied. An amorphous shell composed of silicon oxide is formed on the surface of silicon nanoparticles. The particles form clusters with a fractal structure. The adsorption of nitrogen on a powder of nanocrystalline silicon at 77 K is studied, and adsorption isotherms obtained for nanocrystalline silicon and nonporous silica adsorbents with identical specific surface areas are compared. The values of surface fractal dimension of powdered nanocrystalline silicon are calculated using the Frenkel-Halsey-Hill equation for multilayer adsorption under the dominant contribution of van der Waals or capillary forces. It is shown that surface fractal dimension is a structure-sensitive parameter characterizing both the morphology of clusters and the structure (roughness) of the surface of particles and their aggregates.__________Translated from Kolloidnyi Zhurnal, Vol. 67, No. 4, 2005, pp. 541–547.Original Russian Text Copyright © 2005 by Tutorskii, Belogorokhov, Ishchenko, Storozhenko.     

Material Balance Study of Adsorption of Organic Compounds

It was shown that the structure of a surface complex and the nature of an adsorption bond can be determined from the material balance of adsorption of H⁺and OH^–ions and organic compound. A calculation procedure was considered using adsorption of benzoic acid on silica gel and zirconia as examples. It was established that adsorption of benzoic acid on silica gel was accompanied by the release of H⁺ions resulted from the formation of surface hydrogen bonds, whereas adsorption on zirconia, by the substitution of OH^–ions in coordination sphere of Zr(IV).     

FTIR Studies of the Adsorption of Acetic Acid on Silicas

A range of cesium doped silica samples (0.15 – 0.90 mmol g^–1) have been characterized using a combination of deuterium exchange and adsorption of acetic acid. FTIR results show a strong correlation between the carboxylate formation on acetic acid adsorption and catalyst activity. Cesium loadings of > 0.3 mmol g^–1 do not give any increased acetic acid adsorption, suggesting a saturation of the silica exchange capacity. Deuterium exchange studies demonstrate that 35% of the surface silanol groups on the fresh silica are rapidly exchanged with deuterated water at room temperature.     

Adsorption of Nitrogen,Oxygen, and Argon Vapors on Fine-Pore Oxide Materials

A comparative study of the adsorption of N₂, O₂, and Ar vapors on supermicroporous and fine-mesopore silica at 77 K is carried out. The oxygen sorption properties of these silica materials, like those of tin oxide and zirconia (earlier studied materials), are affected by supermicropores. Argon sorption is insensitive to the presence of supermicropores. Fine mesopores also have an effect on the oxygen sorption properties of silica.__________Translated from Kinetika i Kataliz, Vol. 46, No. 3, 2005, pp. 430–433.Original Russian Text Copyright © 2005 by Gavrilov.     

Equilibrium and Dynamic Characteristics of Protein Adsorption Layers at Gas-Liquid Interfaces: Theoretical and Experimental Data

Within the framework of a nonideal two-dimensional solution model, equations are derived for the state of a surface layer, adsorption isotherms, and the distribution function of adsorbed protein molecules with respect to their states characterized by different molar surface areas. The derived equations satisfactorily describe the known experimental dependences obtained for equilibrium adsorption layers of some proteins (serum albumin, β-casein, and β-lactoglobulin): the dependences of the surface pressure on concentration and adsorption, the surface layer thickness on adsorption, and the limiting high-frequency elastic modulus of an adsorption layer on the surface pressure. All dependences for a given protein are described by the same set of parameters of the theoretical model. It is shown that the kinetics of protein adsorption studied by dynamic tensiometry, ellipsometry, and the radiotracer technique is consistent with the diffusion model comprising the Ward-Tordai equation and the set of equations describing the equilibrium. The kinetics of protein desorption from the adsorption layer at a liquid-fluid interface is analyzed. The kinetics of β-lactoglobulin desorption is shown to be described by the barrier mechanism.__________Translated from Kolloidnyi Zhurnal, Vol. 67, No. 4, 2005, pp. 437–449.Original Russian Text Copyright © 2005 by Fainerman, Miller.     

Characterisation of porous silica. 2. CPG-10 (VYCOR)

Porous silica CPG-10 has been characterised by adsorption of benzene before and after modification with trimethylchlorosilane. The Brunauer–Emmet–Teller (BET) specific surface areas were determined where possible. Modification of CPG-10 reduces its adsorption for benzene and hence reduces the BET specific surface area, with the extent of reduction depending on the extent of modification. For a fully modified sample with the highest surface concentration of trimethylsilyl groups, the adsorption isotherm changes from type IV of the unmodified sample to type V. The hysteresis loop size and position are also altered. A mechanism for multilayer adsorption and capillary condensation in modified porous silica is proposed.     

The adsorption of amino acids on the surface of highly dispersed silica

The adsorption of arginine, histidine, lysine, and ornithine on the surface of highly dispersed silica from aqueous solutions was studied as a function of pH. The equilibrium constants of the formation of surface complexes were calculated using the Stern model for the electrical double layer. It was shown that the possibility of adsorption of amino acids on the silica surface is determined by the presence of additional basic groups in their molecules.Translated from Kolloidnyi Zhurnal, Vol. 66, No. 6, 2004, pp. 733–738.Original Russian Text Copyright © 2004 by Vlasova, Golovkova.     

Thermal Transformations of Titanium Oxochloride Nanostructures on Silica Surface

The nature of thermal transformations of titanium oxochloride surface groups on dispersed silica in the temperature range 25–600°C, both in the course of TiCl₄ chemisorption and in subsequent thermal treatments, is considered.__________Translated from Zhurnal Prikladnoi Khimii, Vol. 78, No. 6, 2005, pp. 881–886.Original Russian Text Copyright © 2005 by Malkov, Sosnov, Malygin.     

31P NMR investigation of the structure of silica surfaces modified by phosphorus trichloride

The structure of the surface chemical compounds on modified pyrogenic silica has been studied in this work by ³¹P magic-angle-spinning NMR spectroscopy. It has been established that the surface silyl dichlorophospite groups (186 ppm) obtained as a result of the reaction of PCl³ with dehydrated silica are hydrolyzed upon the adsorption of water vapor with the formation of phosphorus acid. The thermal treatment of such samples in a vacuum is accompanied by the formation of condensed polyhydrophosphoryl structures.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 24, No. 5, pp. 629–633, September–October, 1988.     

Adsorption of Ethoxylated Alkyl Phenols on Silica Gel from Aqueous Micellar Solutions

Adsorption of ethoxylated nonylphenols (Neonols) from their micellar solutions on coarse-pore KSK silica gel was studied under static conditions. The energy of adsorption interaction between micelles and silica gel surface was determined using the Hill–de Boer isotherm. For the initial parts of the isotherms (from 1 to 6 CMC₁), it was equal to –15.8kT. The study of coadsorption of Neonols with dye methylene blue showed that the micellar adsorption layer is fragmentary and that the amount of the adsorbed surfactant is dependent on the conditions of the adsorption layer formation.     

Intermolecular interactions in liquid adsorption chromatography

Summary For the investigation of intermolecular interactions in adsorption from solution, which are the basis of selectivity in molecular liquid chromatography (LC), it is convenient to use the LC method itself. Using this method the Henry's constants, K₁, and other thermodynamic adsorption characteristics of hydrocarbons and of a series of polar substances on hydroxylated silica surface were determined from aqueous solutions. On the basis of the adsorption of hydrocarbons from water solutions the structure of the chemically modifying layers formed by different hydrocarbon groups on the silica surface is considered. The role of conformation ability of straight-chain bonded phases is demonstrated. Hydrocarbons are adsorbed on the hydroxylated silica surface more strongly from aqueous solutions than from solutions in saturated hydrocarbons and their retention increases with the increase in the number of carbon atoms in the molecule. The retention in LC is determined by the intermolecular interaction of the solute and solvent molecules with the adsorbent, as well by the contribution of the intermolecular interaction, between the solute and the solvent.The thermodynamic characteristics of adsorption of cymarin from water-ethanol solutions on hydroxylated silica gel and on silica gel surface modified by diphenylsilyl groups is compared. The solubility of silica gel modified by diphenylsilyl groups at different composition of water-ethanol eluent at different temperatures is investigated.Enlarged text of a paper presented at the Sixteenth International Symposium on Advances in Chromatography, Barcelona, Spain, September 28–October 1, 1981.     

Effect of preparation pH on pore structure of silica gels

Surface characterization of silica gels prepared at different gelation pH from water glass and sulphuric acid were made by argon adsorption at 77 K using continuous volumetric method. While microporous silica gels prepared in the pH range of 1–3 had BET surface areas of 504–571 m² g^–1, total pore volumes of 0.26–0.31 cm³ g^–1 and micropore volumes of 0.16–0.23 cm³ g^–1, mesoporous silica gels prepared in the pH range of 3.36–0.65 had BET surface areas of 374–530 m² g^–1 and pore volumes of 0.61–0.79 cm³ g^–1.     

Method for Thermodynamic Description of an Elastically Deformed Electrode, Based on Relating Its Extensive Surface Characteristics to a Strainless Electrode

A theoretical approach to thermodynamic describing elastically deformed electrodes made of isotropic materials is suggested. The approach is based on considering the surface of a strainless electrode as a reference one. A surface analog of the Lame elastic constants is introduced. Dependences of the Shuttleworth equation and the Gibbs adsorption equation on the Lame elastic constants characterizing the surface are found in an explicit form.__________Translated from Elektrokhimiya, Vol. 41, No. 8, 2005, pp. 993–996.Original Russian Text Copyright © 2005 by Grafov, Paasch.     

Conversions of ethanol in thermolysis of dyes adsorbed on a silica surface

Using thermal desorption measurements with mass spectrometric analysis of the gas phase, we have studied the characteristics of the interaction of ethanol molecules with the silica surface under conditions when some of the adsorption centers are occupied by molecules of a heteroaromatic dye. The characteristics of the thermal conversions of ethanol on the surface are described in terms of ideas concerning the nature of the active centers on a surface of dispersed silicon dioxide. We observed occurrence of the reaction of ethoxylation of the surface with an increase in temperature. The interaction between the ethanol molecules and the dye molecules occurs with formation of a complex in an excited state upon UV irradiation, which stimulates adsorption of the solvent in strongly bound forms with decomposition of the complex in the surface layer.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 28, No. 1, pp. 87–91, January–February, 1992.     

Microcalorimetric Study of Methanol Adsorption on Initial Silica and Silica Modified with Polyfluoroalkyl Groups

The adsorption of methanol on initial silica and modified silica samples containing large mesopores is studied by the adsorption–calorimetric method. The grafted tridecylfluoroalkyl groups have a tilted orientation on the silica and physically screen the part of the surface OH groups that have not been involved in the reaction with a modifier. Adsorbed methanol makes the modifying layer looser, thus facilitating the accessibility of methanol molecules to these hydrophilic adsorption sites. Concentrations of OH groups involved in the chemical interaction with molecules of the modifier, OH groups physically screened by its organofluoric radicals, and OH groups located on the surface areas free of the modifier are quantitatively estimated. An additional silanization of the modified silica leads to coverage of silica surface areas that are free of organofluoric modifier with trimethylsilyl radicals. The heat of interaction between the methanol molecules and silica surface hydroxyl groups is determined; it is equal to 60 kJ/mol. The structure of the modifying organofluoric layer and changes in this structure that resulted from additional silanization of the surface and from the methanol adsorption are discussed.     

Calculation of the Stoichiometric Composition of Nanostructures Synthesized by Molecular Layer Deposition on the Surface of Solid Matrices

Calculational formulas for determining from the results of chemical and thermogravimetric analyses the true relative contents of components in products formed in molecular layer deposition of nanostructures on the surface of solid matrices are suggested. The approaches considered are illustrated by the example of evaluation of the chemical composition of titanium oxide (nitrogen) and silicon-nitrogen nano-layers synthesized by molecular layer deposition on the silica surface.__________Translated from Zhurnal Prikladnoi Khimii, Vol. 78, No. 3, 2005, pp. 373–379.Original Russian Text Copyright © 2005 by Sosnov, Malkov, Malygin.     

Adsorption–Photometric Determination of Cationic Surfactant Traces

A procedure has been developed for the adsorption–photometric determination of cationic surfactants in natural water. The procedure is based on the adsorption preconcentration of the cationic surfactants on silica gel, the reaction of the concentrate with the anionic reagent bromothymol blue to form ion pairs on a solid surface, and the photometric determination of excess bromothymol blue in solution. The analytical range is (0.5–5) × 10^–5 M for a 50-mL sample.     

Adsorption of cationic and nonionic surfactants on a SiO<Subscript>2</Subscript> surface from aqueous solutions: 1. Adsorption of dodecylpyridinium bromide and Triton X-100 from individual solutions

Adsorption of cationic surfactant dodecylpyridinium bromide and nonionic surfactant Triton X-100 from aqueous solutions on the surface of SiO₂ particles is studied at various pH values (3.6, 6.5, and 10). The data on the adsorption are compared with the data on the wetting of quartz plates by solutions of these surfactants. Adsorption of both studied surfactants on the SiO₂ surface is greatly dependent on solution pH. The mechanism of adsorption of the cationic surfactant is shown to be changed when passing to the alkaline pH region. Triton X-100 does not demonstrate a substantial change in the adsorption mechanism in the pH range from 3.6 to 10.__________Translated from Kolloidnyi Zhurnal, Vol. 67, No. 2, 2005, pp. 274–280.Original Russian Text Copyright © 2005 by Kharitonova, Ivanova, Summ.     

Properties of Monolayers of Long-Chained Aliphatic Compounds Adsorbed at an Amalgamated Platinum Electrode

Electrochemical impedance spectra are obtained in a wide potential range for electrodes covered by monolayers of cetyl alcohol and stearic acid. The conditions for the determination of true values of the monolayer’s capacitance and ohmic resistance are found. It is shown that the restructuring of the stearic acid monolayer in alkaline solutions slightly increases its true resistance and consequently does not involve an increase in its dielectric constant. This validates the assumption on the thinning of the monolayer, which follows from the increase of its capacitance. The short-term adsorption of the above aliphatic compounds results in the formation of a monolayer whose chains are orientated parallel to the electrode surface while during the long-term adsorption, the chains are normal to the surface.__________Translated from Elektrokhimiya, Vol. 41, No. 7, 2005, pp. 872–877.Original Russian Text Copyright © 2005 by Evstefeeva, Khanova.