Stoichiometric decomposition of water by titanium(IV) oxide photocatalyst synthesized in organic media: Effect of synthesis and irradiation conditions on photocatalytic activity
Nano-sized anatase titanium(IV) oxide (TiO2) particles, synthesized by hydrothermal crystallization in organic media (HyCOM), were calcined, platinized, and then used as a photocatalyst for stoichiometric decomposition of liquid water to H2 and O2. The Pt-loaded HyCOM TiO2 photocatalysts showed superior ability to decompose water into H2 and O2 in a molar ratio of 2:1 when they were suspended in water, and their photocatalytic activity depended strongly on the post-calcination temperature (Tc) as well as on the direction of photoirradiation. When the suspension was photoirradiated from the side of a cell, the activity increased with increasing Tc, and HyCOM TiO2 of high crystallinity prepared by calcination at 1273 K exhibited a rate of H2 and O2 libration three-times higher than that of Degussa P-25, one of the most active TiO2s. In a top-irradiation system, the activity was much higher than that of the side-irradiation system and increased with increasing Tc up to 973 K but then decreased, suggesting that the dispersion of TiO2 powders in water, in addition to the crystallinity, is an important factor for stoichiometric water decomposition in this irradiation system.