Enhancement of the photocatalytic activity of ZnO nanoparticles by silver doping for the degradation of AY99 contaminants

Photocatalytic activity of commercial zinc oxide nanoparticles (ZnO) has been investigated and its photocatalytic efficiency improved by loading silver (Ag/ZnO) using UV light. Ag-doping onto ZnO, various mole % (1, 3, 5, 7 and 9) of silver has been investigated for the photoactivity of the doped material in acid yellow 99 (AY99) degradation. The effect of operation parameters such as pH, catalyst dosage, and initial dye concentration was estimated. The optical band gap of the samples was found to be 3.36 eV for ZnO and 3.34 eV for Ag/ZnO (7%), which proves the change in the acceptor level induced by the Ag atoms. Optimal experimental conditions on catalysts amount, pH value, illumination time, and dye concentration have been determined. These catalysts were characterized for surface area, particle size and crystallinity. The mineralization of AY99 has been confirmed by Chemical Oxygen Demand measurements. Furthermore, the kinetics and scavengers of the reactive species during the degradation were also investigated. It was found that the degradation of AY99 fitted the pseudo first-order kinetics and OH center dot radicals were the main species. Formation of OH center dot free radicals during irradiation is established by photoluminescence studies using terephthalic acid as examination molecule. (C) 2019 Elsevier B.V. All rights reserved.