Synthesis of nanometer-sized gallium oxide using graphene oxide template as a photocatalyst for carbon dioxide reduction

Abstract Since the activity of semiconductor photocatalysts for CO2 reduction with water is still low, it is necessary to improve their activity. To do this, the optimization of particle size and crystal structure of the photocatalysts is one of the promising ways. In previous studies, we have reported that micro-particulate Ga2O3 deposited on Al2O3 support significantly improves the photocatalytic activity of CO2 reduction. However, it is quite difficult to synthesize nano-particulate Ga2O3 with high crystallinity by calcination at higher temperatures. In this work, we have tried to synthesize sheet-like nano-particulate Ga2O3 using graphene oxide (GO) as a template for the first time. After loading gallium butoxide on GO, it was calcined to oxidize the gallium butoxide into Ga2O3 and also to remove GO. Various spectroscopic analyses revealed that the synthesized materials were planar aggregation of nanometer-sized Ga2O3 particles (nsGa2O3), of which sizes and crystallinity could be controlled with the calcination temperature. The nsGa2O3 calcined at 1123 K was well crystallized and showed β-phase with a quite large specific surface area. Furthermore, Ag loaded nsGa2O3 calcined at 1123 K (Ag/nsGa2O3(1123 K)) showed very high photocatalytic activity for CO production in the photocatalytic CO2 reduction test in aqueous solution including methanol under UV light irradiation. Thus, it is confirmed that the planar aggregation of nanometer-sized Ga2O3 significantly improves the photocatalytic activity of Ga2O3 on the CO2 reduction.