Mesoporous SiO2-Modified Nanocrystalline TiO2 with High Anatase Thermal Stability and Large Surface Area as Efficient Photocatalyst

Mesoporous SiO2-modified nanocrystalline TiO2 photocatalysts have been prepared by sol-hydrothermal processes, followed by post-treatment with appropriate amount of surfactant F127-modified silica sol. The resulting photocatalysts were also characterized by X-ray diffraction, Raman spectroscopy, Brunauer−Emmett−Teller spectroscopy, N2 adsorption−desorption, transmission electron microscopy, FT-IR, X-ray photoelectron spectroscopy, UV−vis diffuse reflectance spectroscopy, steady state surface photovoltage (SS-SPV), and transient state surface photovoltage (TS-SPV) techniques. The photocatalytic activities of the samples were evaluated by degrading rhodamine B solution under simulated solar illumination. The results show that the surface modification with mesoporous SiO2 greatly enhances the thermal stability of the nanocrystalline anatase TiO2, even still being with a main anatase phase after calcination at 900 °C, and the more is the amount of SiO2 used, the more obvious is the ehancement in the thermal stability. This enhancement is attributed to the effective inhibition of the direct contacts and the diffusions among anatase nanocrystals as well as to the retardation of the crystallite growth. Interestingly, the proper amount of mesoporous SiO2-modified nanocrystalline TiO2 samples by thermal treatment at high temperature can exhibit much higher photocatalytic activity than the commercial-available P25 TiO2, which is explained mainly by the high photoinduced charge carrier separation rate resulting from the high anatase crystallinity based on the analyses of SS-SPV and TS-SPV responses and the large surface area related to the small nanocrystallite size and mesoporous SiO2 as well as still possessing a certain amount of surface hydroxyl group.