ZnS-Ag-ZnO as an Excellent UV-Light-Active Photocatalyst for the Degradation of AV 7, AB 1, RR 120, and RY 84 Dyes: Synthesis, Characterization, and Catalytic Applications

ZnS-loaded Ag-ZnO, synthesized by a precipitation thermal decomposition method, was used for the degradation of four toxic azo dyes, namely, Acid Violet 7 (AV 7), Acid Black 1 (AB 1), Reactive Red 120 (RR 120), and Reactive Yellow 84 CRY 84), under UV light irradiation. To determine the optimum amount of ZnS for the efficient removal of these dyes, the concentration of ZnS was varied with the optimum concentration of 2 wt % Ag. A concentration of 3 wt % ZnS-loaded Ag-ZnO was found to be most efficient in the degradation of these four azo dyes, and this catalyst was characterized by different techniques. Although XRD did not give a Ag peak, the presence of metallic silver was confirmed by XPS measurements. The photocatalytic activity of optimized ZnS-loaded Ag ZnO was compared with those of other catalysts for azo dye degradation. ZnS-Ag-ZnO was found to be more efficient than Ag ZnO, ZnS ZnO, commercial ZnO, prepared ZnO, TiO2, P25, and TiO2 for the degradation of azo dyes under UV light. The mineralization of these four dyes was confirmed by chemical oxygen demand (COD) measurements. A possible mechanism is proposed for the higher efficiency of ZnS Ag ZnO under UV light. This catalyst was found to be reusable and stable under UV light illumination.