Role of surface nature of functional silicas in adsorption of monocarboxylic and bile acids

The chemical modification of silica surfaces by nitrogen-containing organic reagents (γ-aminopropyltriethoxysilane, imidazole, or N-vinyl-2-pyrrolidone) and also with hexamethyl disilazane and hydrocarbon oligomers was proposed to enhance the adsorptive capacity of silica with respect to monocarboxylic and bile acids. The calculation of the content of protonated and deprotonated groups on the surfaces of synthesized organosilicas with distinguished basicity of functional groups was performed using the program GRFIT for the model of a diffuse layer. The contribution of hydrophobic and electrostatic interactions to the adsorption of organic acids was revealed. It has been established that the maximum of organic acid adsorption coincides with the pH at which the curve of increasing concentration of the anion of an organic acid and the curve of decreasing concentration of the protonated functional groups of aminopropyl silica are intercrossed.