Light-induced super-hydrophilicity and photocatalytic activity of mesoporous TiO₂ thin films

Transparent mesoporous TiO₂ (MTiO₂) and TiO₂ nanometer thin films were prepared on fused quartz via the modified reverse micellar and so-gel methods. The MTiO₂ and TiO₂ 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 MTiO₂ thin films at 500 °C showed higher photocatalytic activity and better light-induced hydrophilicity than the TiO₂ thin films. This is attributed to the following reasons: (1) MTiO₂ 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 MTiO₂ particles was beneficial to the transfer and separation of photo-generated electrons and holes inside of and on the surface of TiO₂ particles, and reduced the combination of photo-generated electrons and holes. At 900 °C, the MTiO₂ and TiO₂ 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. Copyright © 2002 Elsevier Science B.V. All rights reserved.