Enhanced visible-light photocatalysis by Au and Ag decorated ZnO for the simultaneous degradation of tetracycline and methylene blue

Pristine and noble metal-decorated ZnO nanostructures were synthesized <i>via</i> a simple chemical reduction approach using hydrazine hydrate to deposit silver (Ag) and gold (Au) nanoparticles. Comprehensive characterization using PXRD, FESEM, HRTEM, XPS, FTIR, Raman, BET, and UV-vis spectroscopy revealed high-surface-area nanostructures with enhanced optical properties. Photocatalytic evaluation demonstrated that Au- and Ag-decorated ZnO exhibited significantly improved degradation efficiencies compared to bare ZnO under visible-light irradiation, attributed to improved charge carrier separation and extended visible-light absorption <i>via</i> plasmonic resonance effects. Notably, the catalysts showed excellent reusability over multiple cycles. Most significantly, the as-synthesized nanocomposite exhibited remarkable capability for the simultaneous co-degradation of two structurally and chemically distinct pollutants: tetracycline (TC, pharmaceutical antibiotic) and methylene blue (MB, textile dye). Under identical visible-light conditions at pH 7, Au-ZnO achieved 95% degradation of TC (2.0 × 10^-3 M) and 80% degradation of MB (1.0 × 10^-5 M) within 120 min using only 20 mg catalyst. This simultaneous removal of pharmaceuticals and dyes in a single photocatalytic process demonstrates the potential of dual-pollutant degradation. The single-platform capability for degrading structurally diverse pollutants suggests that noble metal-modified ZnO warrants further investigation as a multifunctional photocatalyst for treating complex wastewater containing mixed organic contaminants.