Adsorption of benzoic and salicylic acids on modified silicas

To improve the sorbability of silica with respect to organic acids, it was proposed to chemically modify its surface with a nitrogen-containing organi c compound. Methods for chemically attaching imidazole and N-vinyl-2-pyrrol idone at the silica surface and for synthesizing multifunctional silica-bas ed sorbents were developed. The concentrations of protonated and deprotonat ed groups of various basicities at the surface of the synthesized organosil icas were calculated by the GRFIT program within the framework of the diffu sion-layer model. The adsorption values for benzoic and salicylic acids at the surface of hydroxylated amorphous silicas and silicas modified with N-v inyl-2-pyrrolidyl, imidazolyl, and aminopropyl groups were measured. The co ntributions from hydrophobic and electrostatic interactions to the adsorpti on of these organic acids were determined. It was established that the limi ting adsorption of the organic acids occurs at the pH value at which the as cending pH dependence of the concentration of organic acid anions and the d escending pH dependence of the concentration of protonated aminopropylsilic a functional groups intersect.