Synthesis of Defect-Rich ZnO/Cu Schottky Heterojunctions via Flux-Mediated Carbothermal Reduction for Enhanced and Antibacterial Photocatalytic Activity.

The fast recombination of photogenerated charge carriers and the inability to effectively harvest visible light are persistent bottlenecks in utilizing zinc oxide (ZnO) for heterogeneous photocatalysis. In this study, a defect-rich ZnO/Cu (A-ZnO/Cu) Schottky heterojunction was successfully synthesized via a green flux-mediated carbothermal reduction utilizing sodium borate as a flux and carbonized Garcinia mangostana pericarp extract as both a capping and reducing agent. Response surface methodology via a Box-Behnken design was applied to optimize the synthesis conditions. The resulting A-ZnO/Cu sample, synthesized with a ZnO/Cu ratio of 25.56 w/w, calcinated at 644°C for 1.3 h, achieves a malachite green removal efficiency of 99.25%. Comprehensive material characterization elucidated that the synergistic integration of metallic Cu0 structures significantly narrowed the band gap to 2.1 eV and established a robust interfacial Schottky barrier, thoroughly suppressing electron-hole recombination and enabling efficient visible-light-harvesting activity. Radical scavenging experiments confirmed that superoxide radicals and photogenerated holes are the principal reactive species driving the degradation kinetics. Furthermore, the dual-functional nanocomposite demonstrated potent antibacterial activity against Pseudomonas aeruginosa, Staphylococcus aureus, and Salmonella typhi, which was amplified under visible-light illumination. Retaining over 80% of its photocatalytic efficiency after ten cycles, the obtained A-ZnO/Cu heterojunction emerges as a highly durable and promising bimodal agent for environmental remediation and pathogen eradication.