Mesoporous Silica Modified with Titania: Structure and Thermal Stability

Mesoporous silica modified with titania was prepared using the sol−gel process. The structure of these composites was studied using infrared and UV−visible spectroscopies, thermogravimetry, nitrogen sorption measurements, and scanning and transmission electronic microscopies. In light of these results, a model of formation was proposed: the material is composed of a mesoporous silica matrix and small titania particles mainly located at the surface of pore walls. The thermal stability of these composites was investigated from 650 to 1000 °C. It was shown that the increase in temperature leads to the growth of titania nanoparticles associated with the shrinkage of the mesoporous structure. Nevertheless, the whole structure remains mesoporous until 850 °C; the thermal stability is thus improved compared to pure silica or pure titania. At 1000 °C, the composites are nonporous and contain crystallized anatase titania nanoparticles with a mean diameter between 5 and 10 nm embedded in the silica matrix.