Atmosphere-Dependent Electron Relaxation of the Ag-Decorated TiO2 and the Relations with Photocatalytic Properties

Abstract

In the current research, the atmosphere effects on the photoinduced electron relaxations of the undecorated TiO2 and Ag-decorated TiO2 (Ag/TiO2) were carefully studied by means of the in situ photoconductance and diffuse reflection measurements. In pure N2 atmosphere, the results showed that the electron relaxation mainly occurs through the transfer to the residual O2, and the Ag nanoparticles form a fast electron transfer pathway. It was seen that the apparent activation energy of the electron transfer to O2 was greatly reduced by the Ag decoration. In the methanol-containing N2 atmosphere, the electron relaxation can still occur via the transfer to residual O2 in the case of the undecorated TiO2, while the relaxation mechanism changes for the Ag/TiO2 as the relaxations are decreased with the temperatures. It is possible that the methanol molecule adsorbed on the Ag/TiO2 perimeters could act as the bridge for the recombination of the holes and the electrons stored in the Ag nanoparticles. Reducing the Ag nanoparticle size from 15 nm to 3 nm can greatly increase the electron relaxations due to the increase in Ag dispersion and Ag/TiO2 interconnection. Although the electron transfer to O2 was increased, both the photocatalytic oxidations of acetone and isopropanol showed a decrease after the Ag decoration. The results indicated that the photocatalytic oxidation was not limited by the electron transfer to O2. The increased electron transfer to O2 contributed to the recombination around the Ag/TiO2 perimeters, and the photocatalytic activities were decreased.