High-temperature calcination and hydrogen reduction of rutile TiO2: A method to improve the photocatalytic activity for water oxidation

• Particulate rutile TiO2 was calcined at 1100 °C.
• Subsequent H2 reduction at 700 °C improved the photocatalytic activity.
• The hydrogenated TiO2 induce photocatalytic water oxidation efficiently.
• The hydrogenation effect was obtained only for TiO2 calcined at high temperature.
• Oxygen vacancies increase the electron concentration of n-type TiO2.

Rutile titania (TiO2) is an efficient photocatalyst for oxidizing water to O2. The photocatalytic activity of particulate rutile for water oxidation was significantly improved by H2 reduction at 700 °C, after calcination at 1100 °C. The improved activity was due to an increase in crystalline size during calcination, and an increase in conduction band electron concentration by the creation of oxygen vacancies. In contrast to the consideration that oxygen vacancy increases the recombination of electron and holes, the hydrogenated TiO2 exhibited high apparent quantum efficiency for O2 evolution, 41% under irradiation at 365 nm. It was found that H2 treatment improved the photocatalytic activity per unit of surface area not only for O2 evolution but also for H2 evolution and acetic acid decomposition. The effect of H2 reduction treatment was obtained only if the rutile particle was previously calcined at temperatures higher than 1000 °C. This suggests that space charge layer in large crystalline particles is involved in the activation mechanism of hydrogenated rutile TiO2 particles.

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