Effect of Ti3+ Ions and Conduction Band Electrons on Photocatalytic and Photoelectrochemical Activity of Rutile Titania for Water Oxidation

Although TiO2 is generally considered to be an oxygen deficient n-type compound, the role of oxygen vacancies and Ti3+ ions on its photocatalytic activity is not fully understood. In this study, we investigated the effects of high-temperature calcination and H2 reduction treatment on the water oxidation activity of rutile TiO2 under ultraviolet irradiation. Calcination above 900 °C decreased the photocatalytic activity of the TiO2 owing to strong oxidation, but its initial activity was restored by H2 treatment at above 500 °C. Electron spin resonance (ESR) spectra showed that the high-temperature calcination created O•– radicals (trapped hole in oxygen lattice site), while the H2 reduction treatment created Ti3+ ions (trapped electron in titanium lattice site) with oxygen vacancies. Diffuse reflectance ultraviolet–visible–near-infrared (UV–vis–NIR) spectroscopy indicated an increase in the amount of electrons in shallow traps and the conduction band with H2 treatment temperature. Measurements of the sheet...