Thermodynamics of adsorption of organic liquids on Ni-modified solid obtained from collodal silica

Abstract

In order to reduce the well known silica surface inhomogeneity and to get a material suitable for selective chromatographic separations, a modified variety of the material was prepared by a controlled sorption of Ni2+ ions at the solid surface; its adsorption properties were then investigated using the GSC method. Since the starting material was of very high purity, it was possible to follow the influence of Ni2+ ion on the adsorption of various organic liquids, including n-alkanes, cyclohexane, benzene and halomethanes. Adsorption experiments, spanning zero surface coverage and the finite concentration region, were performed in the temperature range from 333 to 443 K. Both the surface activity change resulting from the modification and the possible interactions between the organic substances and the prepared adsorbent were examined using the standard free energy change of adsorption in zero coverage conditions. The adsorption isotherms of all the adsorbates listed were obtained using the Elution by Characteristic Point (ECP) technique and the data were fitted to the BET equation. To get a better insight into the adsorption process in the finite concentration region, the thermodynamic parameters of adsorption were determined and are discussed in terms of surface coverage.