Direct Formation and Photocatalytic Performance of Anatase (TiO ₂ )/Silica (SiO ₂ ) Composite Nanoparticles

Anatase (TiO 2 )/silica (SiO 2 : 23.9–27.7 mol%) composite nanoparticles were directly synthesized from (i) the reaction of titanyl sulfate (TiOSO 4 ) and sodium metasilicate (Na 2 SiO 3 ) under mild hydrothermal conditions, (ii) the acidic precursor solutions of TiOSO 4 and tetraethylorthosilicate (TEOS) by thermal hydrolysis, and (iii) the metal alkoxides, i.e., tetraisopropoxide (TTIP) and TEOS, by the sol–gel method. Their photocatalytic activities were evaluated by measurements of the relative concentration of methylene blue after UV irradiation. The as‐prepared TiO 2 /SiO 2 composite nanoparticles showed far more improved photocatalytic activity than the pure anatase‐type TiO 2 . The composite nanoparticles formed from (i) TiOSO 4 and Na 2 SiO 3 as well as those from (ii) TiOSO 4 and TEOS showed fairly good photocatalytic activity, and it was better than that of those synthesized from (iii) the metal alkoxides, which was suggested to be due to the difference in crystallinity of the anatase.