Hydrothermal synthesis of titania photocatalyst under subcritical and supercritical water conditions

Hydrothermal synthesis of titania powders was carried out under various subcritical and supercritical water conditions using titanium(IV) tetraisopropoxide as a starting material. Characterization of these hydrothermally synthesized titania powders by XRD, TEM, and N-2 adsorption measurements revealed that mesoporous anatase powders can be obtained by simple hydrothermal processing. The average pore size of the titania powders increased from 4 to 25 nm with an increase in the crystallite size of the titania nanoparticles that aggregate to form the mesoporous structure. Based on TG-DTA and FTIR spectra, surface hydroxyl groups decreased with the hydrothermal temperature, indicating that the condensation of Ti-OH accelerates to form a strong network of Ti-O-Ti at higher hydrothermal temperature. The hydrothermally synthesized titania powders were used for photocatalytic hydrogen evolution in an aqueous methanol suspension. Photocatalytic activity of hydrothermally synthesized titania powders was found to be much higher in comparison with some commercial titania photocatalysts. Activities per unit surface area of more than 10 were obtained for the photocatalysts synthesized under subcritical water conditions and between 39 and 68 for those synthesized under supercritical water conditions. The crystallinity is responsible for the highly photocatalytic performance of the titania powders hydrothermally synthesized under supercritical water conditions.