Adsorption properties of bridged polysilylsesquioxane xerogels functionalized with amino, mercapto, and phosphonic groups

Abstract

Adsorption of nitrogen, n-hexane, and triethylamine molecules on polysilylsesquioxane sorbents with an ethylene bridge containing 3-aminopropyl, 3-mecaptopropyl, or simultaneously 3-aminopropyl and 3-mercaptopropyl groups, as well as phosphonic groups, is studied. The adsorption interactions between triethylamine and a sample that contains 3-aminopropyl groups are found to be determined by dispersion forces. Polysilylsesquioxane xerogels that contain either thiol groups solely or thiol and amine groups simultaneously manifest increased adsorptivity with respect to triethylamine molecules compared to n-hexane, which is determined by the formation of hydrogen bonds between adsorbed triethylamine molecules and both -SiOH and -(CH2)3SH surface groups. A very low adsorption of triethylamine is observed on samples that contain phosphonic groups. The corresponding isotherm lies close to P/Ps axis, which indicates the prevalence of repulsion forces between the surface and adsorbed triethylamine molecules. The absence of protondonating sites on the sample is attributed to the interaction of phosphonic groups with each other and with silanol surface groups determined by the globule skeleton structure.