Towards thermally stable aerogel photocatalysts: TiCl4-based sol-gel routes for the design of nanostructured silica-titania aerogel with high photocatalytic activity and outstanding thermal stability

Despite their excellent textural/structural properties, usage of aerogels in photocatalytic applications is critically limited by the necessity of high temperature annealing procedures to improve crystallinity, which lead to drastically decrease in surface area and the undesirable phase transformations. In this study, we report two novel straightforward TiCl4-based sol-gel routes for synthesis of SiO2/TiO2 nanocomposite and SiO2@TiO2 core-shell aerogels with exceptional photocatalytic performance even after annealing at temperatures as high as 1000 degrees C. While core-shell aerogels prepared by thermo-induced deposition method show higher and unprecedented thermal stability, epoxide-assisted gelation method offers greater control over phase composition, allowing preparation of highly photoactive anatase/rutile bicrystalline silica-titania nanocomposite aerogels. The improved structural properties achieved result in an increase of photocatalytic activity of silica-titania aerogels after high temperature annealing at 1000 degrees C. Such unusually high thermal stabilities outperform those shown by previously reported titania and silica-titania materials, representing significant advance on the design of thermally stable photocatalysts for applications that require the catalyst to undergo high temperature processing or endure extreme operating conditions.