Electron energy factors in photocatalytic methylviologen reduction in the presence of semiconductor nanocrystals

Abstract

A linear relationship between the conduction band potential of a number of semiconductor nanocrystals (Cd x Zn 1− x S, CdSe, CdTe, ZnO) and the quantum efficiency of the photocatalytic methylviologen (MV 2+) reduction was found. It reflects dependence between the rate of photoinduced electron transfer from a semiconductor nanophotocatalyst to methylviologen and the overpotential of this process and is not affected by variations in chemical composition of the photocatalytic system. Cadmium selenide nanocrystals were found to have photocatalytic properties in the MV 2+ reduction by sodium sulfite. Differences in the photoprocess kinetics observed for CdSe and Cd x Zn 1− x S nanocrystals indicate that simultaneous photocatalytic reduction of MV + to MV 0 takes place in the case of cadmium selenide. Low efficiency of this process for Cd x Zn 1− x S nanocrystals was interpreted as a result of lowering of the energy of photogenerated electrons due to the surface trapping. The results presented show that the availability, nature, and depth of surface charge traps of a nanophotocatalyst should be taken into consideration when interpreting the kinetics of photocatalytic processes with the participation of semiconductor nanocrystals.