Surface modification of ZnO with Ag improves its photocatalytic efficiency and photostability

Ag/ZnO photocatalysts with different Ag loadings were prepared by photocatalytic reduction of Ag+ on ZnO with ethanol as hole scavenger. It was found that loading an appropriate amount of Ag on ZnO not only enhances its photocatalytic activity, but also improves its photostability. The Ag/ZnO photocatalysts were characterized with XRD, BET, DRUV–vis, Raman, PL, and photoelectrochemical measurement. No matter what the Ag loading is higher or low, silver exists in the form of metallic species in the Ag/ZnO photocatalysts. The enhancement of photocatalytic activity is due to the fact that the modification of ZnO with an appropriate amount of Ag can increase the separation efficiency of photogenerated electrons and holes in ZnO, and the improvement of photostability of ZnO is attributed to a considerable decrease of the surface defect sites of ZnO after the Ag loading. The chemisorption of molecular oxygen and the chemisorption of atomic oxygen on Ag in the Ag/ZnO photocatalysts were observed. It was found that the metallic Ag in the Ag/ZnO photocatalysts does play a new role of O2 chemisorption sites except for electron acceptor, by which chemisorbed molecular oxygen reacts with photogenerated electrons to form active oxygen species, and thus facilitates the trapping of photogenerated electrons and further improves the photocatalytic activity of the Ag/ZnO photocatalysts.