Effects of Deposited Metallic Silver on Nano-ZnO for the Environmental Purification of Dye Pollutants

Abstract

Silver-deposited nano-ZnO samples with different Ag loadings were prepared by a one-pot solvothermal method. The structure, physico-chemical and optical properties of the products were characterized by using X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDS), diffuse reflectance spectroscopy (DRS) and photoluminescence spectra (PLS). The experimental results show that the prepared nanometer zinc oxide powders have a narrow size distribution of 40–60 nm, and their crystal forms can be assigned to hexagonal wurtzite structures. Moreover, the photocatalytic activity of the
samples was examined by using photocatalytic oxidation of methylene blue (MB), as a model reaction, and the effects of the noble metal content on the photocatalytic activity were investigated. The results indicate that the photocatalytic activity of the ZnO nanoparticles can be greatly improved by depositing appropriate amounts of noble metal on their surfaces. In addition, a mechanism was proposed in order to account for the enhanced activity. It is evident that the effective lifetime of photogenerated holes is prolonged by electron-trapping of the metallic silver on the surface of the ZnO nanoparticles. The metal deposits serve as electron sinks, which lead to an enhanced rate of dioxygen reduction, facilitating the generation of hydroxyl radicals, and thereby increasing the photocatalytic activity.

Keywords: Noble metal, electron scavengers, heterogeneous photocatalysis