Green Synthesis of ZnO and CuO Nanoparticles Using Macadamia Nut Shell Extracts: Photocatalytic and Antibacterial Activities

Green synthesis methods have garnered significant attention as eco-friendly alternatives to conventional chemical approaches, which often involve hazardous substances. In this study, macadamia nut shell extract was used as a natural stabilizing and capping agent for the sustainable and environmentally friendly synthesis of zinc oxide nanoparticles (ZnO-NPs) and copper oxide nanoparticles (CuO-NPs). The natural compounds present in the macadamia nut shell extract facilitate the formation of these nanoparticles. The synthesized ZnO and CuO NPs were confirmed by various types of spectroscopic and microscopic techniques. XRD analysis confirmed that ZnO NPs exhibit a hexagonal wurtzite structure, while CuO NPs display a face-centered cubic lattice structure. The green-synthesized nanoparticles demonstrated excellent antioxidant and antimicrobial properties against both Gram-positive and Gram-negative bacteria. Moreover, the photocatalytic efficiency of the nanoparticles was assessed by examining the degradation of tetracycline, with ZnO demonstrating superior performance compared to CuO. The antimicrobial activity of ZnO and CuO NPs was tested against Staphylococcus aureus (strain 902), Escherichia coli (strain 443), Aspergillus niger , and Candida albicans , showing promising results. Furthermore, both ZnO and CuO NPs exhibited synergistic effects when combined with antibiotics. The newly developed green-synthesized ZnO and CuO NPs proved to be simple, cost-effective, and environmentally friendly, and utilized for various applications, including food packaging, biosensors, and catalysis in pharmaceutical reactions.