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

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 N-2 atmosphere, the results showed that the electron relaxation mainly occurs through the transfer to the residual O-2, and the Ag nanoparticles form a fast electron transfer pathway. It was seen that the apparent activation energy of the electron transfer to O-2 was greatly reduced by the Ag decoration. In the methanol-containing N-2 atmosphere, the electron relaxation can still occur via the transfer to residual O-2 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 O-2 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 O-2. The increased electron transfer to O-2 contributed to the recombination around the Ag/TiO2 perimeters, and the photocatalytic activities were decreased.

Automated summary

In this research, the effects of atmosphere on the electron relaxations of undecorated TiO2 and Ag-decorated TiO2 were studied using in situ photoconductance and diffuse reflection measurements. It was found that in a pure N-2 atmosphere, electron relaxation mainly occurred through transfer to residual O-2, with Ag nanoparticles forming a fast electron transfer pathway. The activation energy for electron transfer to O-2 was greatly reduced by Ag decoration. In an N-2 atmosphere containing methanol, the relaxation mechanism changed for Ag/TiO2 as the relaxations decreased with temperature, possibly due to methanol acting as a bridge for hole-electron recombination at the Ag/TiO2 perimeters. Reducing Ag nanoparticle size increased electron relaxations due to increased dispersion and interconnection. However, photocatalytic oxidations showed a decrease after Ag decoration, indicating that they were not limited by electron transfer to O-2.