Photoluminescence Excitation Engineering of Gold Nanoparticle-Decorated Zinc Oxide Nanoflowers for Efficient Visible Photocatalytic Water Treatment

Plasmonic metal–semiconductor heterostructures represent an effective strategy for enhancing visible-light-driven photocatalysis and suppressing charge recombination in wide-bandgap oxides. Here, we report the synthesis of hierarchical Au nanoparticle-decorated ZnO nanoflowers (Au/ZnO NFs) and systematically investigate their plasmon-assisted photocatalytic mechanisms. Structural and compositional analyses confirm that Au nanoparticles are uniformly distributed on the ZnO NF surface without disrupting the wurtzite crystal structure. UV–Vis diffuse reflectance spectroscopy demonstrates enhanced visible-light absorption induced by the localized surface plasmon resonance of Au nanoparticles, while the intrinsic band gap of ZnO remains unchanged. Photophysical investigations using steady-state photoluminescence (PL), PL excitation, and time-resolved PL demonstrate that Au decoration significantly suppresses both near-band-edge and defect-related recombination. This suppression arises from plasmon-induced hot-electron generation, efficient interfacial electron transfer, and electron trapping at the Au–ZnO interface, resulting in prolonged carrier lifetimes and enhanced charge separation. These effects promote the generation of reactive oxygen species under visible-light irradiation. Consequently, the Au/ZnO NFs exhibit enhanced visible-light-driven photocatalytic degradation of methylene blue, achieving nearly complete dye removal within a short irradiation time of 30 min. This study proposes a mechanistic understanding of plasmon-enhanced charge-transfer processes in Au/ZnO heterostructures and establishes a promising strategy for designing efficient visible-light-driven photocatalysts for catalytic wastewater treatment.