Photocatalytic degradation of methyl orange using biogenic Ag–ZnO nanostructures derived from Searsia lancea

Abstract The uncontrolled discharge of synthetic dyes such as methyl orange (MO) into aquatic systems poses significant environmental and health challenges due to their persistence and resistance to conventional treatment methods. In this study, Ag-doped ZnO nanoparticles were synthesized via a green and sustainable route using Searsia lancea leaf extract, with Ag doping levels of 1, 5, 10, and 20%. The materials were characterized for their structural, morphological, and optical properties. A successful incorporation of Ag into the ZnO lattice was confirmed by X-ray diffraction (XRD), Fourier transform infrared (FTIR), and Ultraviolet-visible spectroscopy (UV-vis spectroscopy). Ag doping induced a surface plasmon resonance effect, reducing the bandgap and extending light absorption from the UV to the visible region. The bandgap energy decreased from 3.36 eV (pristine) to 3.29, 3.00, and 2.76 eV with 1, 5, and 10% Ag doping, respectively, indicating modified electronic properties. The photocatalytic activity of the green-synthesised ZnO and Ag-doped ZnO catalysts was evaluated for MO degradation under visible light irradiation over 120 min. Pristine ZnO achieved 61.35% degradation, while Ag/ZnO exhibited significantly enhanced performance, with 1, 5, 10, and 20% doping achieving 93.20, 98.06, 99.35, and 95.85% efficiencies, respectively. The optimal 10% Ag/ZnO catalyst was further tested for the degradation of other pollutants, including crystal violet and ibuprofen, yielding efficiencies of 84.9% and 83.3%. The results highlight green synthesis as a viable route for producing highly active Ag-doped ZnO photocatalysts with application in wastewater treatment.