Yu. I. Tarasevich

Quantum Chemical Study of the Interaction of Water Molecules with a Partially Oxidized Graphite Surface

Quantum chemical (MNDO-PM3) and molecular mechanical calculations are presented for some models describing the interaction of water molecules with hydrophilic adsorption centres on the initial and oxidized basal surface of graphitized carbon black particles. The fact that the calculation results are in reasonable agreement with available experimental data indicates the capability of the methods used to describe the properties of such adsorption systems.

Complexing sorbents based on dispersed minerals for recovery of heavy metal ions from aqueous solutions

We have obtained sorbents for recovery of heavy metal ions from aqueous solutions by modification of kaolinite and metakaolinite, aluminum oxyhydroxide and aluminum hydroxide by polyphosphates. Using sorption of Ni2+, Co2+ and Cr3+ as an example, we have shown that the sorbents have high sorption capacity and distribution coefficient with respect to heavy metal ions. We have studied the composition of the complexes formed. We have developed methods for granulation of the sorbents with a binder and for regeneration of the sorbents.

Interaction of water and other polar substances with hydrophilic centres on the surface of hydrophobic adsorbents

The adsorption of water and other polar substances on to the surface of graphitized carbon black and macroporous silica modified by polymethylhydride silicone has been studied using gas chromatography. The adsorption heat values of the substances studied were determined and the concentration of surface hydrophilic centres estimated. Conclusions have been drawn concerning the number of water molecules adsorbed on to hydrophilic centres at low surface occupation values. In the case of water adsorption on the graphitized carbon black surface, the chromatographic data for the adsorption heat have been compared with the energy of water molecule interaction with the surface clusters modelling the micropores existing on the basal surface of carbon black particles as calculated using quantum chemical methods.

Study of the Structure of a Surface-porous Adsorbent using the Gas Chromatographic Version of the Molecular Probe method

Results are presented of structural studies of a silica-based surface-porous adsorbent. It is shown that a reliable estimate of the size of the surface micropores of this adsorbent can be obtained using the gas chromatographic version of the molecular probe method. This is based on a comparison of the thermodynamic properties for the adsorption of substances of known molecular size on the surface-porous adsorbent with those characteristic for the adsorption of the same substances on to a non-porous adsorbent of a similar chemical nature.

Non-Specific Adsorption of Hydrocarbons on Microporous Surfaces: A Comprehensive Molecular-Statistical/Chromatographic Approach

The results are presented of a series of investigations concerning the application of the molecular-statistical approach to the calculation of thermodynamic quantities for the adsorption of molecules in the Henry region on adsorbent surfaces possessing certain surface symmetry properties, and in particular for systems characterized by dispersion and polarization attraction and short-range atom-atom repulsion. Computational methods have been developed and the results for particular adsorption systems are presented with emphasis on the adsorption properties of layer silicates. Good correspondence between the calculated results and chromatographic data for a number of adsorbents strongly supports the view that the combination of chromatographic and molecular-statistical methods provides a powerful tool for the investigation of the structural and adsorption-selective characteristics of surface-porous adsorbents.

A calorimetric adsorption study on the interaction of water with hydroxylated surface of γ-Al2O3

The curve for the differential heat of adsorption of water on γ aluminum oxide has parts related to the interaction of the adsorbed water molecules with surface molecules of coordinated water and with acid and basic hydroxyl groups. Estimates have been made of the effective charges and hydration numbers for three of these adsorption centers. Textural changes have been observed in the γ-Al2O3 particles related to interplate swelling in the secondary sorbent packets into which the primary particles are linked.

Ion-exchange equilibria and exchange heats on clinoptilolite involving singly-charged cations

Isotherms and integral heats of exchange of alkali metal, ammonium, and silver cations on sodium clinoptilolite were measured. Exchange involving K+, NH4+, Cs+, and Ag+ displacing cations was found to be exothermic for all occupanciesθ of the clinoptilolite exchange sites. Exchange was exothermic for Li+ cations up toθ = 0.15. The dependence of the differential ion-exchange heats onθ was determined. Clinoptilolite was found to have two types of exchange sites with different heats of ion exchange. The experimental data were used to calculate the selectivity coefficients, thermodynamic constants, and ion-exchange entropy. These findings are discussed relative to the differences in the cation properties and structural features of clinoptilolite.

Modification of Natural Layered Silicates with Rigid Structure by Polyhexamethylene Guanidine

A new approach is proposed for creating modified materials entailing the selection of matrix-modifier pairs, in which the structural characteristics of the components, namely, the distance between the ion-exchange sites on the matrix surface and distance between the active groups in the modifier, are similar. A procedure was developed for the modification of layered silicates with rigid structure using polyhexamethylene guanidine without a greater-than-equivalent amount of modifier. It is shown that modifier is held firmly by inorganic matrix.

Physicochemical principles for developing new materials based on silicate dispersed minerals

We consider the physicochemical principles for obtaining effective new sorbents, catalysts, supports, and fillers made from natural dispersed minerals using heat treatment, modification by inorganic and organic compounds, stratification of carbon layers, introduction of inorganic and organic oligomers and polymers into the structure of the minerals. We discuss the properties and practical use of the new materials.

Current status and prospects for development of research on the hydrophilicity of disperse systems

The current status of research on the hydrophilicity of disperse systems was discussed. The criterial values of the surface pressure of the adsorbed water film, heat and contact angle of wetting with water which separate the hydrophilic and hydrophobic surfaces were determined. An analysis of the thermodynamic characteristics showed that the boundary layers of water are more ordered near a hydrophilic surface (mica, kaolinite) and less ordered near a hydrophobic surface (organokaolinite, graphite) in comparison to liquid water. The biexponential character of the change in the structural component of the disjoining pressure with the thickness of the water film was demonstrated for disperse materials with a hydrophilic surface (kaolinite). The classification of the forms of water bound by hydrophilic disperse materials was discussed. The changes in the thermodynamic functions of vermiculite in adsorption of water were found with complex adsorptioncalorimetric and dilatometric measurements. This adsorbent undergoes a first-order phase transition during adsorption. The prospects for use of the adsorption-calorimetric method for determining the amount and energy characteristics of hydrophilic sites was demonstrated for ZSM-5 hydrophobic zeolite.