Selective Surface Modification of SiO2-TiO2 Supports with Phosphonic Acids

The selective surface modification by phosphonic acids of SiO2-TiO2 supports at the micrometer and molecular scale was investigated. Under aqueous conditions, phosphonic acids bind to TiO2 and not to SiO2 surfaces. A micropatterned support was prepared by electron beam microlithography and selectivity, of the surface modification was evidenced using scanning Auger electron spectroscopy (SAES). The second support was a mesoporous SiO2-TiO2 mixed oxide (10 mol % Ti) epoxidation catalyst prepared by sol-gel processing. Selectivity was deduced from the decrease of the catalytic activity upon modification and from chemical analysis; bonding modes to the surface were investigated using solid-state 29Si and 31P MAS NMR. The possibility to introduce different organic groups by successive treatments with a phosphonic acid and a silylating agent was illustrated in the case of the mixed oxide.