Polymer-assisted freeze-drying synthesis of Ag-doped ZnO nanoparticles with enhanced photocatalytic activity

Ag-doped ZnO nanoparticles with high and stable photocatalytic activity were prepared by polymer-assisted freeze-drying method with simple process and without organic solvents used. The structural morphology and optical properties of Ag-doped ZnO nanoparticles were characterized by X-ray Diffraction (XRD), Inductive Coupled Plasma Optical Emission Spectrometry (ICP-OES), Field Emission Scanning Electron Microscopy (FESEM), Transmission Electron Microscopy (TEM) and high resolution TEM (HRTEM) with energy dispersive Xray spectroscopy, Ultraviolet-visible Diffuse Reflectance Spectroscopy (UV-vis DRS), X-ray Photoelectron Spectroscopy (XPS) and Fourier Transmission Infrared Spectroscopy (FTIR). Moreover, the thermoanalytical measurements (TGA-DTG) analysis is carried out for proper calcination temperature. XRD results show that Ag nanoparticles were successfully doped into ZnO lattice, and UV vis DRS results indicate that the doped Ag nanoparticles result in ZnO exhibiting enhanced light trapping capability in the 400 nm and 600 nm range. The photocatalytic activity of Ag-doped ZnO was examined by analyzing the degradation of methyl orange (MO) and methylene blue (MB) dyes under UV light and solar light irradiation, and the results show that all Ag-doped ZnO nanoparticles exhibit better photocatalytic activity than those of pure ZnO nanoparticles at the same degradation conditions; especially the synthesized Ag-ZnO nanoparticles are easy to be recycled and have high photocatalytic stability. Based on the experimental results, the photocatalytic electron transfer path and the photocatalytic mechanism of Ag-ZnO nanoparticles under UV and solar irradiation conditions are explained and clarified.