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 techn ology. The material incorporates an organic substituent, propyl-N,N,N-trime thylammonium, which is linked to the silica matrix covalently. This materia l is anion exchangeable and exhibits an improved selectivity toward chlorid e over more lipophilic anions. It is optically transparent and has been cha racterized by thermogravimetric analysis, infrared spectroscopy, nitrogen s orption analysis, capillary electrophoresis, cyclic voltammetry, and measur ement of membrane potential. The material is porous, and almost all the cov alently linked organic substituents are active in the pore space. The surfa ce charge of this material is switchable in sign and its magnitude is depen dent 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.