Self-assembly of titanias having surface organic moieties and development of visible-light responsible photocatalytic materials

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Thermal reaction of titanium tetraisopropoxide and tetraethyl orthosilicate in 1,4-butanediol (glycothermal method) afforded nanocrystalline silica-modified titanias having large surface area and superior thermal stability. In this study, the thus-obtained silica-modified titanias were treated in an NH_3 flow at high temperatures, and their physical and photocatalytic properties were investigated. Compared with NH_3-treated TiO_2 without silica modification, the NH_3-treated silica-modified titanias showed a stronger absorption in the visible region (400-500 nm) and had a larger peak at 396 eV in the N 1s XPS spectrum. These results indicate that a larger amount of nitrogen was stably doped in the silica-modified titania. The obtained products exhibited a high photocatalytic activity for degradation of Rhodamine B and decomposition of acetaldehyde under visible light irradiation. Nanocrystalline titanias modified with various elements (B, Mg, Al, P, Zn, and Ga) were also prepared by the glycothermal method and the obtained samples were nitrified in the same way. Among the six modifiers examined, addition of P was the most effective for photocatalytic decomposition of acetaldehyde under visible-light irradiation. After nitrification and annealing, the P-modified titania showed a strong absorption in the visible region (400-550 nm). It was found that the photocatalytic activity was related to the amount of nitrogen atoms doped in the anatase structure.