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

A linear relationship between the conduction band potential of a number of semiconductor nanocrystals (CdxZn1−xS, CdSe, CdTe, ZnO) and the quantum efficiency of the photocatalytic methylviologen (MV2+) 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. m selenide nanocrystals were found to have photocatalytic properties in the MV2+ reduction by sodium sulfite. Differences in the photoprocess kinetics observed for CdSe and CdxZn1−xS nanocrystals indicate that simultaneous photocatalytic reduction of MV+ to MV0 takes place in the case of cadmium selenide. Low efficiency of this process for CdxZn1−xS 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.