Infrared study of the adsorption of oleic and linolenic acids onto the surface of silica immersed in carbon tetrachloride

Abstract

The adsorption of oleic acid and linolenic acid onto silica from carbon tetrachloride solution has been studied by infrared spectroscopy. At the lowest surface coverages studied adsorption of acid monomer onto pairs of adjacent silanol groups occurred. As the concentration of acid in solution was increased adsorption of monomer onto isolated surface silanol groups became predominant. At high solute concentrations some evidence was also observed for adsorbed acid dimers. The primary adsorptive interaction involved the formation of hydrogen-bonds between surface hydroxyl groups and the carboxylic acid groups of the adsorbate molecules. However simultaneous interaction of the oxide surface with the alkene residues of the alkyl chains occurred. Evacuation and heat treatment of silica covered with an adsorbed layer of linolenic acid led to the elimination of molecular water and the formation of chemisorbed linolenate groups on the oxide surface.