Adsorption properties of the surface of Silochrome S-80 modified with aluminium alizarinate

Abstract

Silica-based materials are widely used in the processes of concentration and separation of various organic substances. Successful use of SiO2 is due to its chemical resistance, thermal stability, the nature and distribution of functional groups on the surface, as well as the possibility of creating materials based on it with certain textural characteristics, which are regulated by synthesis conditions and surface modification. For the solution of specific problems of chromatography, it is necessary to obtain new adsorbents with fixed functional groups, layers or elements, by varying which the number and types of adsorption centres of the original surface change. Chelate complexes of transition metals, including those deposited in the form of adsorption layers, are used as promising modifying additives of particular interest. In this work, SiO2 based on Silochrome S-80, modified with aluminium alizarinate was studied by physicochemical method. Using thermogravimetry it was established that aluminium alizarinate is stable up to 270 °C. Using adsorption porosimetry, it was shown that modification of silica leads to a decrease in the average diameters and total volumes of pores, and specific surface areas from 84 to 79 m²/g. Using IR and Raman spectroscopy, the fixation of chelates on the surface of Silochrome was proven. The gas chromatographic method was used to study the adsorption processes of organic compounds (n-alkanes, nitromethane, heptene-1, aromatic hydrocarbons, ketones and alcohols) capable of various types of intermolecular interactions. The modification of silica with an alizarin-containing complex contributes to a change in the Henry adsorption constants and the contributions of specific interactions to the heat of adsorption. In this case, the highest values of ∆ q̅dif,1(special) are characteristic of organic compounds prone to donor-acceptor and π-complex formation. According to the analysis of compensation thermodynamic dependencies q̅dif,1 - ∆S̅S1,c it was shown that entropy is the determining thermodynamic parameter during the adsorption of test compounds on the surface of the studied chromatographic materials.