Mesophase configurations and optical properties of mesoporous TiO2 thin films

Highly ordered mesoporous TiO2 thin films have been successfully synthesized via a copolymer templating sol-gel route. A configuration transition from hexagonal, to cubic, and then to a channel-like structure was observed when the copolymer-templated thin film was thermally annealed from 110 to 450 degrees C. In the mesoporous TiO2 film annealed at 450 degrees C, mesopores were merged in a preferential direction, forming a channel-like structure consisting of a semicrystalline (anatase) framework. These films exhibit excellent optical transparency with transmittance higher than 85% in the visible region. A blue shift in UV-Vis absorption onset was shown for the mesoporous TiO2 films, indicating a size quantization effect of nanocrystalline titania.