Hydrothermal Preparation And Photocatalytic Activity Of Hierarchicall Sponge-like Macro/mesoporous Titania

To solve the increasingly serious problems of environmental pollution, various catalytic techniques are being applied in the fields of environmental protection. Oxide semiconductor photocatalysis is one technique that has great potential to control aqueous organic contaminates or air pollutants. Among various oxide semiconductors, TiO₂ has been proved to be the most suitable photocatalyst for its strong oxidizing power, nontoxicity and long-term stability against photo and chemical corrosion. In recent years, many attempts, such as finding new preparation methods and using modifications, have been made to improve the photocatalytic activity of TiO₂. However, the preparation of photocatalyst with highly photocatalytic activity, the immobilization of powder photocatalyst, and the improvement of photocatalyst performance are priorities to be considered. Herein, valuable explorations have been carried out on the synthesis of highly active TiO₂ photocatalysts. The main points could be summarized as follows:A new concept "biomemitic photocatalysis" has been proposed, which may provide new insight into preparation of advanced photocatalytic materials by mimicing surface structures of plant leaves. Trimodally sponge-like macro/mesoporous titania was prepared by hydrothermal treatment of precipitates of tetrabutyl titanate (Ti(OC₄H₉)₄) in pure water. Effects of hydrothermal time on the phase composition, porosity and photocatalytic activity of hierarchically porous titania were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM) and N₂ adsorption-desorption measurements. All TiO₂ powders prepared at 180℃showed trimodal pore-size distributions in the macro/mesoporous region. With increasing hydrothermal time, crystallinity, average anatase crystallite size, pore size and pore volume increased, while specific surface area decreased. The hierarchically porous titania prepared at 180℃for 24h displayed an especially high photocatalytic activity probably due to its special pore-wall structure and its photocatalytic activity was about three times higher than that of Degussa P-25. Highly photoactive nanocrystalline Au modified TiO₂ powders were prepared by impregnation method. The results showed that photocatalytic activity of the Au modified TiO₂ powders exceed that of pure P25. The photocatalytic activity of modified TiO₂ was strongly dependent on the Au dopant level. The P25 powders modified using 300μL 1mM Au colloids showed the highest photocatalytic activity. This was ascribed to the fact that an optimal amount of Au in the powders effectively reduced the recombination of photo-generated electron-hole pairs on the surface of TiO₂ powders.