Defect Engineering of Pt/TiO<sub>2–<i>x</i></sub> Photocatalysts via Reduction Treatment Assisted by Hydrogen Spillover
Yukari Yamazaki, Kohsuke Mori, Yasutaka Kuwahara, Hisayoshi Kobayashi, Hiromi Yamashita
Abstract
Defect engineering of metal oxides is a facile and promising strategy to improve their photocatalytic activity. In the present study, Pt/TiO2–x was prepared by a reduction treatment assisted by hydrogen spillover to pure rutile, anatase, and brookite and was subsequently used for hydrogen production from an aqueous methanol solution. With increasing reduction temperature, the photocatalytic activity of the rutile Pt/TiO2–x increased substantially, whereas the activity of anatase Pt/TiO2–x decreased and that of brookite Pt/TiO2–x was independent of the treatment temperature. Electron-spin resonance analysis revealed that rutile and brookite possess similar defect sites (Ti3+ and concomitant oxygen vacancy) after the reduction at 600 °C, whereas different resonance signals were observed for anatase after the reduction at 600 °C. During the reduction process, electrons donated from spillover hydrogen migrate between the conduction band and the inherent midgap states. This research demonstrates that the depth of the inherent midgap states, depending on the crystal phases, influences the generation of defects, which play a key role in the photocatalytic performance of Pt/TiO2–x.