Abstract:The photo-induced hydrophilicity of SiO₂overlayer on TiO₂films prepared by sol-gel method was investigated by means of soak angle measurement, XPS, UV-VIS and FTIR spectra. The results show that, compared with the TiO₂ film without SiO₂overlayer, when the TiO₂film is thoroughly covered by SiO₂overlayer, the hydrophilicity and the sustained effect are enhanced. It is found that the significant growth of the OH-group occurs in the surface of SiO₂overlayer. The different mechanism of enhanced hydrophilicity between SiO₂ overlayer on TiO₂films and TiO₂/ SiO₂mixing films was analyzed. The result suggests that the photo-generated electrons created in the interface between TiO₂ and SiO₂ tendto reduce the Ti(Ⅳ) cation to the Ti(Ⅲ) state, and the photogenerated holes transmit through the SiO₂ layer to upper most surface efficiently. Once the holes go up to the surface, they tend to make the surface hydrophilic. The stable hydrophilicity of SiO₂ overlayer which adsorbs more stable OH groups, enhances the sustained effect, i.e. the super-hy drophilic state can be maintained for a long time in dark place.

Key words: TiO₂; SiO₂; super-hydrophilic property; overlayer films; sol-gel method