Synthesis-Dependent Oxidation State of Platinum on TiO2 and Their Influences on the Solar Simulated Photocatalytic Hydrogen Production from Water

Platinized TiO 2 photocatalysts of different compositions of Pt 0 and PtO 2 were prepared by modifying the synthesis procedures. The physicochemical properties of the composite materials were characterized by X-ray photoelectron spectroscopy and high-resolution transmission electron microscopy. Energy dispersive X-ray spectroscopy measurements confirmed the presence of Pt species existing as PtO 2 and/or mixtures of Pt 0 and PtO 2 . The composite material, Pt–TiO 2 –2%H, contained a high amount of metallic Pt 0 and PtO 2 in close proximity with TiO 2 that promoted an enhanced photocatalytic hydrogen evolution activity under simulated solar light irradiation. Although Pt–TiO 2 –2%C and Pt–TiO 2 –2%T consisted of similar compositions of PtO 2, these oxidized platinum species seem to appear further apart from TiO 2 in Pt–TiO 2 –2%C than Pt–TiO 2 –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 prepared by the conventional photodeposition method was also prepared, characterized, and its photocatalytic activity assessed. This work provides an opportunity to understand the role of PtO 2 for photocatalytic production of hydrogen from platinized TiO 2 composites and the importance of heterojunctions in such photocatalysts for solar energy conversion.