Effect of Au nanoparticles and Au mesostars on the photocatalytic activity of ZnO nanorods

The major drawback of Zinc Oxide (ZnO) as a photocatalyst is high recombination rate. The composite ZnO nanorods (NRs) with noble metal particles is a promising structure for reduction of recombination rate. In this study, we compare the effect of Au nanoparticles (NPs) with a diameter of 20-40 nm and the Au mesostars (MSs) with a size of 100-500 nm on the photocatalytic properties of ZnO nanorods. The electron-rich sites in sharp branches of Au Mss are expected to increase the photocatalytic activity. The results show that the addition of Au NPs enhances the degradation rate of methylene blue from 30% to 40%, while the addition of Au MSs actually reduced the activity to 28%. It maybe due to the eroded ZnO NR's surface during the deposition of Au MSs, hence the whole of surface area of ZnO NRs is decreased. The electron transfer from ZnO to Au MSs indicated in PL spectrum does not seem to be enough to compensate the production of photogenerated electrons and holes in the sharp branches of Au mesostars.