Ag species in the Ag loaded Ga₂O₃ (Ag/Ga₂O₃) photocatalysts were investigated with regard to changes in their structures and the chemical states before and after the photocatalytic CO₂ reduction with water. Ag clusters with the size of around one nanometer in as prepared 0.1 wt% Ag/Ga₂O₃ sample became larger metallic Ag nanoparticles with the size of several nanometers after the reaction. In the 1.0 wt% Ag/Ga₂O₃ sample, Ag nanoparticles having the AgGaO₂ interface structure decomposed to aggregated Ag metal particles after the reaction. Such transition in the morphology and chemical states of Ag species could explain the variations in photocatalytic activities of these samples during the reaction, and suggested that at least metallic Ag particles would function as effective co-catalysts.

In-situ FT-IR measurements of the Ag/Ga₂O₃ samples before and after the reaction, we could not detect CO₂ molecules adsorbing on metallic Ag nanoparticles in dark. Under light irradiation, however, the absorption bands originated from the photo-adsorbed CO₂ species on Ag metal nanoparticles appeared. Thus, we detected the interaction of CO₂ molecules and metallic Ag nanoparticles as the effective co-catalysts for CO₂ reduction.

研究了负载有Ag _2的Ga ₂ O ₃（Ag / Ga ₂ O ₃）光催化剂中的Ag种类，研究了其在结构上的变化以及在水催化还原CO ₂之前和之后的化学状态。在所制备的0.1重量％的Ag / Ga ₂ O ₃样品中，具有约1纳米的尺寸的Ag簇在反应后变成具有几纳米的尺寸的较大的金属Ag纳米颗粒。在1.0wt％的Ag / Ga ₂ O ₃样品中，具有AgGaO _2的Ag纳米颗粒反应后，界面结构分解为聚集的Ag金属颗粒。Ag物种的形态和化学状态的这种转变可以解释这些样品在反应过程中光催化活性的变化，并暗示至少金属Ag颗粒将充当有效的助催化剂。

反应前后对Ag / Ga ₂ O ₃样品进行原位FT-IR测量，我们无法在黑暗中检测到吸附在金属Ag纳米颗粒上的CO ₂分子。然而，在光照射下，出现了源自Ag金属纳米颗粒上的光吸附CO ₂物种的吸收带。因此，我们检测到CO ₂分子与金属Ag纳米颗粒的相互作用作为有效的CO ₂还原助催化剂。