Hydrophilicity of anatase TiO2/Cr-doped TiO2 thin films with different band gaps

Based on the concept that the electron-hole separation effect caused by a different band-gap structure would improve its hydrophilicity, anatase-TiO2/Cr-doped TiO2 thin films were synthesized by DC magnetron sputtering. The optical band gaps of TiO2 thin films decreased from 3.23 to 2.95 eV with increasing Cr-doping content. Multilayer TiO2 thin films with different band gaps exhibited a superhydrophilicity under UV illumination. In particular, in anatase TiO2 (3.23 eV)/4.8% Cr-doped TiO2 (2.95 eV), the hydrophilicity, which indicated a contact angle of less than 20, lasted for 48 h in the dark after UV illumination was discontinued. This outstanding result has rarely been reported for TiO2 thin films, which confirmed that the prominent superhydrophilicity of anatase TiO2/Cr-doped TiO2/glass could be attributed to the retardation of electron-hole recombination caused by the band-gap difference. Crown Copyright (C) 2011 Published by Elsevier B.V. All rights reserved.