Photocatalysis and hydrophilicity of doped TiO2 thin films

TiO2 thin films were prepared using the dip-coating method with a polymeric sol including additives such as Al, W, and Al + W to examine two major properties: photocatalysis and hydrophilicity. W-doped films showed the best photocatalytic efficiency, while Al-doped film was poorer than undoped samples. However, good hydrophilicity in terms of saturation contact angle and surface conversion rate was found in Al- and (Al + W)-mixed-doped films. It was found that deep electron-hole traps and high surface acidity of W-doped TiO2 thin film were the major factors in high photocatalytic efficiency. In addition, low surface acidities of Al- and (Al + W)-doped films provided better hydrophilicity than W-doped ones. However, the amount of [Ti3+] point defects on the surface was another major factor, probably the most important, in getting the best hydrophilicity. Conclusively, it seemed that many parts of the photocatalysis mechanism depend more on bulk-related properties than do those of hydrophilicity, which can be defined as an interfacial (surface) or near-surface-restricted process. (C) 2003 Elsevier Inc. All rights reserved.