Synthesis of Ag nanoparticles prepared by a solution plasma method and application as a cocatalyst for photocatalytic reduction of carbon dioxide with water

Silver nanoparticles (Ag NPs) were synthesized by a solution plasma method (SPM) in an aqueous solution of ammonia. Optical emission spectra of the plasma revealed that Ag NPs are fabricated with the sputtering of Ag rods as electrode by the produced energetic plasma particles such as H, OH and O radicals. In-situ optical absorption measurements of the solution during the discharge directly presented the concerted formation and aggregation processes of the Ag NPs, which controlled the size of Ag NPs. The synthesized Ag NPs were loaded on gallium oxide (Ga2O3) photocatalyst, and the photocatalytic activities of the obtained Ag loaded Ga2O3 (Ag/Ga2O3) samples were evaluated. Although the photocatalytic reaction proceeded over all the samples to produce CO, the CO production rates decreased with the reaction time. Measurements of DR UV-vis spectra and TEM images revealed that a part of the Ag NPs migrated and aggregated on the photocatalyst surface to become larger particles during the photocatalytic reaction, which would be related to the decrease of the photocatalytic activity. It was also found that the photoirradiation treatment on the prepared Ag/Ga2O3 sample before the use for the photocatalytic reaction improves the photocatalytic performance.