Light-induced super-hydrophilicity and photocatalytic activity of mesoporous TiO 2 thin films

Abstract

Transparent mesoporous TiO 2 (MTiO 2) and TiO 2 nanometer thin films were prepared on fused quartz via the modified reverse micellar and sol–gel methods. The MTiO 2 and TiO 2 films were characterized by X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), X-ray diffraction (XRD), BET surface area and UV–Vis spectrophotometry. The photoinduced super-hydrophilicity and photocatalytic activity of the films were evaluated by the water contact angle measurement and photocatalytic oxidation of acetone in air, respectively. It was found that MTiO 2 thin films at 500 °C showed higher photocatalytic activity and better light-induced hydrophilicity than the TiO 2 thin films. This is attributed to the following reasons: (1) MTiO 2 thin films are composed of smaller monodisperse spherical particles about 15 nm diameter, and possess more mesopores between spherical particles and higher surface areas and surface roughness, (2) the monodispersity of MTiO 2 particles was beneficial to the transfer and separation of photo-generated electrons and holes inside of and on the surface of TiO 2 particles, and reduced the recombination of photo-generated electrons and holes. At 900 °C, the MTiO 2 and TiO 2 films appeared to be in the rutile phase, but showed photoinduced hydrophilicity and no photocatalytic activity. This confirmed that the mechanism of photoinduced super-hydrophilicity of the films is different from that of photocatalytic oxidation.