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(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 N-2 adsorption-desorption measurements. All TiO2 powders prepared at 180 degrees 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 mu m. 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 degrees 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.