Yu.I. Tarasevich

Hydrophilicity- Hydrophobicity Characteristics of Solid Surfaces and the State of Water near Surfaces of a Various Nature

Values for the surface tension, π, of 85 mJ/m2 and for the contact angle of wetting by water as its saturated vapour, θV, of 75° are proposed as criteria for distinguishing between hydrophilic and hydrophobic solid surfaces. It is shown that the water boundary layers at hydrophilic surfaces are more ordered while those at hydrophobic surfaces are less ordered relative to the situation in the bulk water structure. The localised model can be used to describe the state of motion of water molecules at a hydrophilic surface, while the motion of water molecules near a hydrophobic surface conforms to the non-localised model.

Application of natural adsorbents and adsorption-active materials based thereon in the processes of water purification

Publisher Summary This chapter demonstrates that natural sorbents of various types and adsorption-active materials based thereon can readily be used for the removal of three groups of impurities from water. The three main types of natural sorbents can be distinguished with respect to the features of their structure, chemical composition, porosity, and physicochemical properties: silica, layer and layer-ribbon silicates, and framework aluminosilicates (zeolites). Dispersed impurities—clay particles, humic substances, bacteria and viruses, finely emulsified oil, and petroleum products—are removed from water using filtration, coagulation, flocculation, and flotation methods. One common method of water purification from dispersed particles is filtration through a porous medium; natural sorbents are efficiently applied for this purpose. Layer silicates montmorillonite, and kaolinite—although among dispersed impurities that should be removed from drinking water—rather paradoxically can be used to purify drinking and waste water from suspended particles. Combined use of these minerals with flocculants or small amounts of coagulants is recommended for more intensive and complete precipitation of dispersed silicate particles with bacteria and viruses adhered to them.

Effect of the carbonaceous matter deposition on the textural and surface properties of complex carbon-mineral adsorbents prepared on the basis of palygorskite

Abstract Natural palygorskite spent in adsorption process of paraffin purification was used for the preparation of carbon-mineral adsorbents. The waste material containing 10.88% w/w carbonaceous matter was treated in three ways: (1) direct pyrolysis at 400°C with a suitable temperature programme; (2) preliminary hydrothermal modification (200°C, 8 h, 13.5 atm.) and then thermal treatment as in method 1 and (3) preliminary thermal (400°C) and then chemical treatments (boiling in 3% Na 2 CO 3 solution), next heating at 500°C (10 min). The carbon-mineral adsorbents prepared in this way included 3.07, 3.47 and 2.18% C w/w, respectively. These were determined the following characteristics of the prepared adsorbents: porous and crystal structure parameters, as well as, chemical composition, carbon deposit topography on the mineral matrix surface and adsorption heat of the test substances. It was stated that thermal and hydrothermal treatments did not cause significant changes in the parameters of natural palygorskite porous structure. Such changes are caused by the presence of carbon deposit on the mineral matrix whose topography and morphology depend on the type of treatment used for the prepared palygorskite. Carbon deposit is located mainly in mesopores diminishing their volume. At the same time, a number of narrow pores of a radius equal to about 1.9 nm increases compared with the initial palygorskite. Carbon deposit blocks the strongest adsorption/catalytic centres partially or completely and as a result adsorption heat of the test substances ( n -hexane, dichloromethane, tetrachloromethane) on the carbonised adsorbents decrease with the increase of carbon deposit amount in the complex adsorbent.

Chapter 2.9 Molecular statistic and gas chromatographic study of hydrocarbons adsorption on the modified layer silicates and silica in the Henry region

Publisher Summary The studies presented in this chapter are based essentially on the principle of comparison of the thermodynamic characteristics of adsorption measured on a number of organoderivatives of layer silicates and silica, with the data obtained from the molecular statistic calculations involving the portions of surface, which model the real surface of the materials studied. These surface portions are chosen on the basis of the adsorbent structure analysis and complex physico-chemical studies of the modifying layers structure. When performing the studies summarized in the chapter, also the principle of structural chemical modeling is extensively used, which imply the comparison of the results of chromatographic experiments on the adsorbents possessing predicted separation centers with those on the adsorbents that have only a small number of such centers, if any. The identification of the portions of chromatographic materials, on which the adsorption and separation processes take place, has formed a scientific background for the development of new efficient adsorbents and supports for the chromatography. This chapter reviews the results of the studies mentioned above.

Statistical-mechanical derivation of generalised langmuir equation and its application for the interpretation of chromatographic data for the adsorption of water and methanol on non-porous carbon materials

The chromatographic method is applied to the study of water and methanol adsorption on non-porous carbon materials—graphitised carbon black and thermally expanded graphite. It is shown that the processing of the experimental isotherms in coordinates of the classic Langmuir equation results in their linearization in two ranges of relative pressure, indicating the presence of two types of adsorption centres on the surface, which can be identified as the carboxyl and phenolic hydroxyl groups, respectively. A generalised Langmuir equation based on a statistical-mechanical approach is proposed, capable for the description of both monomolecular and polymolecular adsorption on the surface. It is shown that this equation provides for a better description of the adsorption of polar molecules on non-porous carbon materials.

Gas chromatographic, quentum-chemical, and molecular statistical studies of cluster adsorption of water and methanol molecules on hydrophilic surface sites of hydrophobic adsorbents

The comprehensive theoretical and experimental study of the adsorption of water and methanol molecules on active sites (carboxyl and phenol hydroxyl groups) on the graphitized thermal carbon black is performed. It is shown that microclusters formed upon the adsorption of these molecules on such sites are characterized by the cyclic structure comprising 4–5 molecules similar to that whose existence was revealed previously in liquid water and on the surface of silver iodide. The analysis of the studied adsorption clusters demonstrated that the formation of such cycles is governed primarily by the hydrogen bonding; however, a definite role is played also by energy effects associated with the changes in the state of molecular motion during adsorption. It is shown that the generalized Langmuir equation derived from molecular statistical considerations provides for better reproducing of the experimental isotherm within a wider surface coverage range, thus making it possible to consistently interpret data on structural and energetic characteristics of adsorption systems obtained by gas chromatography and quentum-chemical method.

Calorimetric studies of ion-exchange equilibria on clinoptilolite involving unicharged cations

Abstract Isotherms and integral heats of exchange for alkali metals, ammonium, and silver cations on sodium clinoptilolite were studied. Exchange involving K+, NH4+, Cs+, and Ag+ cations was found to be exothermic for all occupation degrees θ of the clinoptilolite exchange sites, while for Li+ cations the exchange was exothermic up to θ ≈ 0.15. The dependence of the differential ion-exchange heats vs θ was studied. 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 results are discussed from the viewpoint of the differences in the cation properties and structural features of clinoptilolite.

Preparation of a Modified Adsorbent Based on Clinoptilolite and Its Application for The Removal of Iron and Manganese Ions from Artesian Water

A method is developed for the modification of the external surface of clinoptilolite grains by manganese dioxide. This modified clinoptilolite is shown to be an efficient material for the post-purification of artesian drinking water with respect to iron ions and the removal of Mn2+ ions from this water: 1 kg of adsorbent is capable for cleaning up to 600 dm3 of artesian water containing 1.2 - 1.4 mg/dm3 Mn2+ ions without regeneration. Optimum conditions for the regeneration of spent adsorbent by potassium permanganate are determined.

Quantum-chemical modeling of Li+ exchange ions of layer silicates

Through quantum-chemical modeling (MNDO method), a realistic description has been obtained for the structure of a section of the basal surface in a dioctahedral layer silicate without any isomorphous substitution, namely (SiO2H)6[Al(OH2)2OH]2OH, and with isomorphous substitutions Al → Si in the tetrahedral network and Mg → Al in the octahedral network, with compensation of unit negative charge by an Li+ cation that may be either anhydrous or hydrated with one to four water molecules. The positioning of a small trigonal cation in a ditrigonal hole on the surface of an anhydrous or partly dehydrated layer silicate is shown to be a property of a structure with nonstoichiometric isomorphism in the octahedral network rather than in the tetrahedral network. A study has been made of the interrelation between the positions of the exchange cation in the hole and the proton of the hydroxyl group forming the bottom of the hole. Values calculated for the enthalpy of hydration of the Li+ cation by three successive molecules of water are in satisfactory agreement with the experimental values.

Adsorption studies of organosubstituted laminated silicates

The hysteresis of sorptive deformation of sorbents has been studied for the first time. Based on the results obtained, it is assumed that the deformation of sorbents could be the universal reason for the sorptive hysteresis.