Direct Solvothermal Formation of Nanocrystalline TiO2 on Porous SiO2 Adsorbent and Photocatalytic Removal of Nitrogen Oxides in Air over TiO2–SiO2 Composites

Solvothermal decomposition of titanium(IV) tert-butoxide (TTB) in toluene at 573 K in the presence of silica gel (SiO2) with continuous stirring yielded a titanium(IV) oxide (TiO2)–SiO2 composite in which agglomerates of nanocrystalline TiO2 were deposited on the surfaces of SiO2 particles. Various TiO2–SiO2 composites having different TiO2 contents can be synthesized by changing the ratio of TTB and SiO2, and the composites had large surface areas corresponding to porous properties of SiO2. These TiO2–SiO2 composites were used for photocatalytic removal of nitrogen oxides in air and their photocatalytic performances were compared with those of other TiO2–SiO2 samples prepared by different methods. Solvothermally synthesized 74 wt.%TiO2–SiO2 composite exhibited excellent photocatalytic performance (almost stoichiometric removal of NO x (98%) and very low NO2 release (0.3%)) attributable to high photocatalytic activity of TiO2 and high adsorption property of SiO2. Lesser performance of 74 wt.%TiO2–SiO2 composites prepared by other methods suggested that pore-mouth plugging of SiO2 by TiO2 and lower level of mixing of TiO2 and SiO2 decreased photocatalytic performance of the composites.