Low-temperature synthesis and characterization of TiO2 and TiO2–ZrO2 photocatalytically active thin films

Transparent TiO2 and TiO2–ZrO2 (molar ratio Zr/Ti = 0.1) thin films were produced by low-temperature sol–gel processing from nanocrystalline aqueous based solutions. The structural features and compositions of the films treated at room temperature, 100 °C and 500 °C were investigated by X-ray diffraction, X-ray photoelectron spectroscopy and thermal analysis. Addition of zirconia increased specific surface area (140–230 m2 g−1) and hindered the growth of anatase crystallites, exhibiting a constant size of 6–7 nm in the whole temperature range. These significant changes with respect to pure TiO2 in anatase crystalline form did not result in significantly and systematically different photocatalytic activity, which was evaluated in terms of aqueous pollutant degradation (azo-dye in water) and self-cleaning ability (fatty contaminant deposit). The films treated at only 100 °C showed excellent photocatalytic activity towards azo-dye degradation. Contact angle measurements of aged and contaminated surfaces revealed a fast or sharp hydrophilicity gain under UVA illumination. Accordingly, the results of this study confirmed the potential application of advantageous low-temperature films in water treatment as well as for self-cleaning surfaces.