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Thin films of various metal oxides were prepared on glass substrates by a wet process to determine their photocatalytic ability to decompose adsorbed dye and to evaluate their photoinduced hydrophilicity under UV illumination. The metal oxides used in this study are classified into four categories based on their behavior over the two photochemical reaction: (1) active in both photocatalytic oxidation and photoinduced hydrophilicity (TiO2, SnO2, ZnO); (2) only active in photocatalytic oxidation (SrTiO3); (3) only active in photoinduced hydrophilicity (WO3, V2O5); (4) and inactive over both processes (CeO2, CuO, MoO3, Fe2O3, Cr2O3, In2O3). X-ray photoelectron spectroscopy revealed that oxygen defect sites were produced by Ar+ bombardment on the surface of metal oxides, showing photoinduced hydrophilicity. These results indicate that photoinduced hydrophilicity is not induced by the photocatalytic oxidation of organic compounds adsorbed on the surface, but is based on structural changes of the metal oxide surfaces.
Miyauchi et al. (Wed,) studied this question.