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.