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

Toward the realization of carbon neutrality by utilizing renewable energy sources, photocatalytic conversion of CO2 with H2O, known as artificial photosynthesis, should be important because H2O is harmless and an abundant source of protons for CO2 reduction. Many researchers focusing on the photocatalytic conversion of CO2 have revealed that the Ag nanoparticle was an effective co-catalyst for the selective conversion of CO2 to CO in water. To improve the activity for the photocatalytic conversion of CO2 in water, it is important to modify the surface of the photocatalysts to load small Ag nanoparticles with high dispersity, which is difficult when using conventional methods. In this study, the ultrasonic reduction (USR) method was used as an advanced modification method of photocatalysts with the Ag co-catalyst. We found that Ag/ZnTa2O6 prepared by the USR method showed good selectivity toward CO (> 90 %) evolution and a higher formation rate of CO than those by conventional modification methods. High-Resolution Transmission Electron Microscopy (HR-TEM) images of the Ag co-catalyst clarified that Ag nanoparticles with the size of a single nanometer were loaded on the surface of ZnTa2O6 by the USR method, whereas much bigger Ag particles were observed in the case of the other methods. Accordingly, it can be noted that a small Ag co-catalyst with a single nanometer exhibits superior activity toward selective conversion of CO2 to CO. We herein successfully achieved a high formation rate of CO with high selectivity using the Ag/ZnTa2O6 photocatalyst prepared by the USR method.