Hydrogen and Oxygen Photoproduction by Titanate Powders

Uncoated powders of TiO 2 or SrTiO 3 did not produce H 2 or O 2 on UV irradiation of aqueous suspensions of the powders. TiO 2 powders coated with platinum or rhodium photoproduced H 2 on irradiation (effective wavelengths 334 and 366 nm) and the reaction was stimulated by catalytic quantities of methyl viologen. The turnover numbers for H 2 production relative to TiO 2 were very low suggesting that the powders were not acting catalytically. Hydrogen production was never stoichiometric with respect to TiO 2 and the kinetics of H 2 production were first order, not zero order as would be expected for catalytic photolysis of water. Oxygen was never detected and it appears that H 2 did not arise from water photolysis but rather from oxidation of reduced sites in TiO 2 . A rhodium‐coated SrTiO 3 powder prepared photochemically produced both H 2 and O 2 on irradiation but the turnover numbers were very low. A Rh‐SrTiO 3 powder prepared thermally showed higher turnover numbers for H 2 photoproduction and may be acting catalytically. However, little O 2 was detected with this powder. When the turnover numbers for the different titanate powders were expressed with respect to the number of surface monolayer hydroxyl groups calculated from the surface area of the powders, some turnover numbers greater than one were obtained.