Photocatalytic H2 evolution for α-, β-, γ-Ga2O3 and suppression of hydrolysis of γ-Ga2O3 by adjusting pH, adding a sacrificial agent or loading a cocatalyst

Abstract

In contrast to α- and β-Ga₂O₃ which have already been studied as photocatalysts for pure water splitting, there has been no report on the γ-phase. A comparative study on α-, β- and γ-Ga₂O₃ all prepared by a precipitation method was therefore performed. The as-prepared gallium oxides were phase-identified by powder X-ray diffraction, where γ-Ga₂O₃ possessed the most broad reflection peaks due to poor crystallization. Scanning electron microscopy and N₂ adsorption–desorption experiments confirmed the morphology, and the specific surface areas were 144.3, 30.7, and 77.3 m² g⁻¹ for γ-, β- and α-Ga₂O₃, respectively. Photocatalytic H₂ evolution efficiency in pure water was determined to be in the order of γ-Ga₂O₃ > α-Ga₂O₃ > β-Ga₂O₃, and the efficiencies were all much higher than that of P25–1 wt% Ag. A slight hydrolysis process was observed for γ-Ga₂O₃. Both lowering the pH value (∼4.5) by H₂SO₄ and adding sacrificial agent (CH₃OH) were applied to prohibit the hydrolysis completely. Eventually, 1 wt% Ag was loaded as a cocatalyst in order to not only improve the stability but also to increase the H₂ generation rate to 742 μmol h⁻¹ g⁻¹ in pure water. In addition, for this particular photocatalyst, the optimal apparent quantum yield achieved at 254 nm was 8.34%. Our work represents the first study of γ-Ga₂O₃ in the application of photocatalytic water splitting, and indeed it might have a high potential in solar energy conversion.