Transparent mesoporous nanocomposite films for self-cleaning applications

A versatile approach is studied for the elaboration of TiO₂ based photocatalytic coatings for self-cleaning applications on transparent substrates. The basic principle of the synthesis relies on the use of preformed TiO₂ colloidal particles that are further dispersed within a transparent silica binder with a mesoporous structure. Film porosity in the nanometer range is controlled by achieving the sol-gel silica condensation around self-organized micellar assemblies of a templating copolymer surfactant. The latter also acts as a stabilizer for the TiO₂ particles, thus preserving their high dispersion within the film so that excellent optical properties are maintained even for high TiO₂ loading (up to 50 %). Studies of photodegradation kinetics show that such mesoporous films are at least 15 times more active than films synthesized with a usual microporous silica binder. Moreover, the measured quantum-yield efficiency (1.1 %) is found to be among the highest reported up to now. Improved photoactivity of the films is discussed as resulting from the closer proximity between the organic molecules and the surface of the TiC₂ crystallites as well as the improved diffusion rate of water and oxygen through the interconnected pore network.