Development of visible light sensitive metal oxide photocatalysts having a functional accumulation properties by controlling surface structure

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A new method to dope Fe^<3+> ions only onto the surface of S-or N-doped TiO_2 is proposed. The photocatalytic activities of Fe^<3+> ions adsorbed on S-or N-doped TiO_2 photocatalysts for oxidation of 2-propanol are markedly improved compared to those of S-or N-doped TiO_2 without treatment of Fe^<3+> ions under a wide range of incident light wavelengths, including UV light and visible light. When the amount of Fe^<3+> ions adsorbed on S-doped TiO_2 particles was 0.90 wt%, photocatalytic activity reached maximum. In the case of N-doped TiO_2 with Fe^<3+> ions, the optimum amount of Fe^<3+> ions was 0.36 wt%. The photocatalytic activities of Fe^<3+> ions adsorbed on S-or N-doped TiO_2 photocatalysts decreased gradually when the amount of Fe^<3+> ions was greater than 1.0 wt%. In addition, when S-or N-doped TiO_2 photocatalysts adsorbed with Fe^<3+> ions was observed after reduction by NaBH_4 followed by air oxidation, further improvement in their photocatalytic activities were observed. … More In this case, the optimum amounts of Fe^<3+> adsorbed on the surfaces of S-and N-doped TiO_2 photocatalysts were 2.81 and 0.88 wt%, respectively. During the treatment, Fe^<3+> ions adsorbed on S-or N-doped TiO_2 were reduced to generate metal Fe, and Fe was reoxidized again to form Fe^<3+> ions under an aerated condition. After the treatment, the crystal structure of Fe^<3+> ions adsorbed on S-doped TiO_2 and adsorbtivity of 2-propanol on the photocatalyst were changed.Surfaces of SiO_2-covered TiO_2 photocatalysts (SiO_2-TiO_2) were modified with alkylsilyl groups such as hydrocarbon, fluorocarbon, and phenyl groups. Oxidation of propanal, hexanal, nonanal, pentafuluorobenzaldehyde, and benzaldehyde proceeded much more efficiently on the surface-modified SiO_2-TiO_2 particles than on SiO_2-TiO_2 photocatalysts without surface modification. In the case of SiO_2-TiO_2 photocatalysts modified with hydrocarbon chains, one of most important factors for improvement of the photocatalytic activities of surface-modified TiO_2 photocatalysts is the hydrophobic interaction between substrates and alkylsilyl groups introduced onto SiO_2-TiO_2 photocatalysts. SiO_2-TiO_2 modified with phenyl groups is more active in the photocatalytic oxidation of benzaldehyde than SiO_2-TiO_2-C_6. Furthermore, oxidation of pentafluorobenzaldehyde proceeded more favorably on SiO_2-TiO_2-C_8(F) chains than on SiO_2-TiO_2-C_8. These results indicated that the functional groups introduced onto the surface of SiO_2-TiO_2 play an important role in showing selectivity for photocatalytic oxidation of organic compounds. Less