Tuning the UV-Vis Light Shielding and Photocatalytic Activity of ZnO via Ag⁺/Fe³⁺ Doping and Annealing

ZnO exhibits good sunscreen properties; however, its effectiveness against UVA and visible light still requires improvement. In this study, a simple chemical precipitation method combined with annealing treatment and the introduction of silver ions (Ag⁺) and ferric ions (Fe³⁺) was employed to modify the structure of ZnO particles and evaluate their effects on UV-Vis light transmittance and photocatalytic activities. ZnO, Ag⁺-doped ZnO, and Fe³⁺-doped ZnO particles were prepared by varying the molar ratios of silver nitrate or iron sulfate to zinc hydroxide, followed by annealing at 70, 200, 300, 400, and 500 °C. X-ray diffraction (XRD) and Fourier-transform infrared (FTIR) spectroscopy analyses revealed changes in the crystal structure of ZnO after annealing and Ag⁺/Fe³⁺ doping. UV-Vis spectroscopy measurements showed that both annealing temperature and metal ion doping significantly reduced light transmittance. As the annealing temperature raised and the doping concentrations of Ag⁺ and Fe³⁺ increased, the light transmittance of ZnO particles decreased accordingly. In particular, Ag⁺-doped ZnO particles exhibited the best shielding performance against UVA, UVB, and visible light. Photocatalytic experiments using phenol as a model degradant revealed that appropriate Ag⁺ and Fe³⁺ doping reduced the photocatalytic activity of ZnO particles. In this study, ZnO particles annealed at 500 °C, along with Ag⁺-doped ZnO and Fe³⁺-doped ZnO prepared with optimal doping amounts of 2.81 wt % Ag⁺ and 3.63 wt % Fe³⁺, respectively, exhibited the lowest photocatalytic activity.