Biogenic synthesis of ZnO NPs, CuO NPs, and ZnO/CuO nanocomposites for facile degradation of organic pollutants and biomedical applications

The continuous increase in population and industrial activity in several areas, including textiles, leather, plastics, cosmetics, and food processing, produces harmful organic pollutants such as azo dyes, which are harmful to aquatic life and cause water pollution. The remediation of these dyes using photo-responsive metallic nanoparticles (NPs) has become a viable technique for the purification of water. This study synthesized ZnO NPs, CuO NPs, and ZnO/CuO nanocomposites using <i>A. nilotica</i> leaf extract. The NPs and NCs were characterized by UV-Vis spectroscopy, FTIR, SEM, EDX, ZP, and PXRD. All the nanomaterials showed energy bandgap in the UV and visible light region (2.15-3.00 eV) evidenced by Tauc's plots, successful capping of NPs by organic moieties, identified by FTIR, and crystallite size in the range of 13.72-16.82 nm, calculated by the PXRD data utilizing the Debye-Scherrer equation and quasi spherical shape analyzed by SEM. Compared to ZnO NPs and CuO NPs, ZnO/CuO NCs showed significantly increased photocatalytic performance of 96% for MB dye degradation and 93% for MO dye degradation in 100 min with rate constant (<i>k</i>) values of about 3.35 × 10^-2 min^-1 and 2.65 × 10^-2 min^-1, respectively. The effect of catalyst dose, pH, water composition, and radical scavengers was also evaluated to optimize the conditions and propose a degradation mechanism and p-n heterojunction with Fermi level shifting for improved exciton generation. The biomedical importance of the ZnO/CuO NCs was assessed by the disc diffusion assay to check the antibacterial potential, and DPPH assay, TFC assay and TPC assay for antioxidant potential. All these studies, along with the reusability of the catalyst, demonstrated the appreciable catalytic efficacy of ZnO/CuO NCs for the water purification of industrial effluents.