Low-Temperature Synthesis of Mesoporous Titania-Silica Films with Pre-Formed Anatase Nanocrystals

Titania-silica composite films with a high content of crystalline titania phase and periodic mesoporous structure were fabricated by a low temperature "brick and mortar" approach. Pre-formed titania nanocrystals were fused with surfactant-templated sol-gel silica, which acts as a structure-directing matrix and as a chemical glue. The nature of the surfactant plays the decisive role in the mesostructure formation. Using Pluronic P123 as the structure-directing agent, the structure formation of the mesoporous silica is greatly disturbed as a result of the presence of titania nanoparticles. On the contrary, the use of Pluronic F127, whose molecules are larger and whose poly(ethylene oxide) blocks are more hydrophilic, enables the preparation of composite titania-silica mesoporous architectures that can accommodate up to 50 wt % of nanocrystals and yet retain the periodicity of the porous structure. In this way, films with a high degree of crystallinity were obtained at temperatures as low as 100-150 degrees C and employed as active layers for the photooxidation of NO. The surface of the titania particles is not deactivated with respect to their photocatalytic activity by the surrounding silica matrix or by covalently attached ligands. The "brick and mortar" approach results in periodic mesoporous nanocomposites with photocatalytically active sites leading to functional coatings that are processed at low temperatures and thus opens new perspectives for their applicability on a wide range of substrates.