Microwave-assisted Au-doped ZnO nanostructures with enhanced charge separation for highly efficient rhodamine 6G...

Microwave-assisted hydrothermal Au-doped ZnO nanostructures (1-5 wt% Au) were synthesized using CTAB as a rapid and scalable route to multifunctional nanomaterials. Comprehensive advanced characterization (XRD, XPS, UV-Vis DRS, PL, FE-SEM/TEM, and BET) confirmed phase-pure wurtzite ZnO with successful Au incorporation and Au-driven modulation of the crystallite size, defect density, and surface texture. The optimized 1 wt% Au-ZnO exhibited a reduced crystallite size (38.82 nm) with an increased dislocation density, a slightly tuned band gap (3.17 eV), and an enhanced specific surface area among the series, enabling improved charge separation through the Schottky junction. As a result, 1 wt% Au-ZnO delivered the best photocatalytic performance toward rhodamine 6G, achieving 99.25% degradation within 60 min and an apparent rate constant of 4.85 × 10^-2 min^-1, while maintaining high activity over three reuse cycles. The same composition also exhibited enhanced chemiresistive NO₂ sensing, with a maximum response at 250 °C, fast response time (10 s at 5 ppm), and a monotonic, near-linear increase in sensitivity up to 94 at 40 ppm NO₂. The enhanced performance is attributed to the synergistic effects of Au-induced interfacial band bending, increased oxygen-vacancy-related adsorption/activation, and improved surface reaction kinetics, establishing Au-ZnO as a stable dual-functional platform for integrated dye degradation and NO₂ detection.