Photocatalytic Activity of Ga₂O₃ Supported on Al₂O₃ for Water Splitting and CO₂ Reduction

Abstract

We have examined the photocatalytic activity of Ga₂O₃ supported on Al₂O₃ (Ga₂O₃/Al₂O₃ catalyst) without a noble metal cocatalyst for water splitting and reduction of CO₂ with water under UV light irradiation by changing the loading amount of Ga₂O₃. All prepared Ga₂O₃/Al₂O₃ catalysts show photocatalytic activities for both water splitting and CO₂ reduction, and their activities are significantly improved compared to those of nonsupported Ga₂O₃ and Al₂O₃. The water splitting is dominated for Ga₂O₃/Al₂O₃ with less than 1.0 vol % of Ga₂O₃ loaded, whereas the CO₂ reduction, for higher Ga₂O₃-loaded samples (2.6, 4.2 vol %). Crystalline structure characterizations of Ga₂O₃/Al₂O₃ catalysts indicate that active sites for both reactions are different. The water splitting proceeds on nanometer-sized Ga₂O₃ rods dispersed on an Al₂O₃ support consisting of a little distorted α-Ga₂O₃ phase. On the other hand, the CO₂ reduction proceeds on sub-micrometer-sized Ga₂O₃ particles consisting of mixed phases of α-Ga₂O₃ and γ-Ga₂O₃ or with appearance of boundaries between the α and γ phases, which plays a critical role. Al₂O₃ used as the support of the Ga₂O₃ particles does not seem to play an important role in the photocatalytic CO₂ reduction.