Synthesis-dependent oxidation state of platinum on TiO2 and their influences on the solar simulated photocatalytic hydrogen production from water.

Platinized TiO2 photocatalysts of different compns. of Pt0 and PtO2 were prepd. by modifying the synthesis procedures. The physicochem. properties of the composite materials were characterized by XPS and high-resoln. transmission electron microscopy. Energy dispersive X-ray spectroscopy measurements confirmed the presence of Pt species existing as PtO2 and/or mixts. of Pt0 and PtO2. The composite material, Pt-TiO2-2%H, contained a high amt. of metallic Pt0 and PtO2 in close proximity with TiO2 that promoted an enhanced photocatalytic hydrogen evolution activity under simulated solar light irradn. Although Pt-TiO2-2%C and Pt-TiO2-2%T consisted of similar compns. of PtO2, these oxidized platinum species seem to appear further apart from TiO2 in Pt-TiO2-2%C than Pt-TiO2-2%T. This caused dramatic variation in their optical behaviors such as strong fluorescence quenching and lower photocatalytic hydrogen evolution activity in the former photocatalyst. A photocatalyst prepd. by the conventional photodeposition method was also prepd., characterized, and its photocatalytic activity assessed. This work provides an opportunity to understand the role of PtO2 for photocatalytic prodn. of hydrogen from platinized TiO2 composites and the importance of heterojunctions in such photocatalysts for solar energy conversion. [on SciFinder(R)]