Anion-exchange material with pH-switchable surface charge prepared by sol-gel processing of an organofunctional silicon alkoxide

A novel organofunctional silica material has been prepared by sol-gel technology. The material incorporates an organic substituent, propyl-N,N,N-trimethylammonium, which is linked to the silica matrix covalently. This material is anion exchangeable and exhibits an improved selectivity toward chloride over more lipophilic anions. It is optically transparent and has been characterized by thermogravimetric analysis, infrared spectroscopy, nitrogen sorption analysis, capillary electrophoresis, cyclic voltammetry, and measurement of membrane potential. The material is porous, and almost all the covalently linked organic substituents are active in the pore space. The surface charge of this material is switchable in sign and its magnitude is dependent on pH and type of buffer. The potential of this material as a charged surface coating for capillary electrophoresis or an anion-exchange film for potentiometric sensors has been explored.