Hydrothermal Preparation and Photocatalytic Activity of Hierarchically Sponge-like Macro-/Mesoporous Titania

Trimodally sponge-like macro-/mesoporous titania was prepared by hydrothermal treatment of precipitates of tetrabutyl titanate (Ti(OC 4 H 9 ) 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 N 2 adsorption−desorption measurements. All TiO 2 powders prepared at 180 °C showed trimodal pore-size distributions in the macro-/mesoporous region: fine intraparticle mesopores with peak pore diameters of ca. 3.7−6.9 nm, larger interparticle mesopores with peak pore diameters of ca. 23−39 nm, and macropore with pore diameter of ca. 0.5−3 μm. With increasing hydrothermal time, crystallinity, and average anatase crystallite size, pore size and pore volume increased, while specific surface area decreased. The hierarchically porous titania prepared at 180 °C for 24 h 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. This trimodally sponge-like macro-mesostructured titania could find its varieties of potential applications in photocatalysis, catalysis, solar cell, and separation and purification processes. A new concept “biomemitic photocatalysis” has been proposed, which may provide new insight into preparation of advanced photocatalytic materials by mimicking surface structures of plant leaves.