Ag co-catalyst prepared by ultrasonic reduction method for efficient photocatalytic conversion of CO2 with H2O using ZnTa2O6 photocatalyst

Towards the realisation of carbon neutrality by utilising renewable energy sources, the photocatalytic conversion of CO2 with H2O-known as artificial photosynthesis-is important because H2O is non-toxic or non-hazardous, and an abundant source of protons for CO2 reduction. Many studies on the photocatalytic conversion of CO2 have revealed that Ag nanoparticles are an effective co-catalyst for the selective conversion of CO2 to CO in water. To improve the activity of the photocatalytic conversion of CO2 in water, modifying the surface of the photocatalyst is essential to load small Ag nanoparticles with high dispersity, which is difficult to achieve using conventional methods. In this study, ultrasonic reduction (USR) was used as an advanced modification method for photocatalysts with an Ag co-catalyst. Ag/ZnTa2O6 prepared using the USR method exhibited good selectivity towards CO (>90%) evolution and a higher CO formation rate compared to those prepared using the conventional modification methods. High-resolution transmission electron microscopy images of the Ag co-catalyst revealed that Ag nanoparticles with a size of a single nanometre were loaded onto the surface of ZnTa2O6 by the USR method, whereas much larger Ag particles loaded onto it were observed in the case of other methods. Accordingly, a small Ag co-catalyst with a single nanometre size exhibits superior activity towards the selective conversion of CO2 to CO. Thus, we successfully achieved a high CO formation rate with high selectivity using a Ag/ZnTa2O6 photocatalyst prepared via USR.