Impact of NiO concentration on the optical and biological properties of ZnO:NiO nanocomposites

ZnO:NiO semiconductor nanocomposites have garnered attention in numerous fields, not just antibacterial ones. The current study focuses on preparing pure ZnO (zinc oxide) and ZnO:NiO (nickel oxide) nanocomposites containing different amounts of (5% and 10%). These samples were synthesized utilizing an echo-friendly, cost-effective green approach that employs Phyllanthus emblica fruit extract as a reduction agent. The x-ray diffraction (XRD) peaks correspond to the hexagonal ZnO phase and the cubic NiO phase, with typical crystallite sizes of about 21 and 18nm, respectively. Energy-dispersive X-ray spectroscopy (EDS) confirms the presence of Zn, Ni, and O constituents in the nanocomposites. The field emission scanning electron microscopy (FESEM) image showed the mixed shape of ZnO:NiO nanocomposites, which was a mix of almost spherical and hexagonal forms. A spectral investigation of UV-visible revealed a redshift in the absorption band edge of pristine ZnO nanoparticles with increasing NiO content, indicating a progressive decrease in the optical band gap. ZnO:NiO nanocomposites have lower band gap energy due to crystal lattice strain. Photoluminescence tests revealed high levels of Ni2+ ions in ZnO:NiO nanocomposites, which improved distortion centers and lattice surface defects in ZnO, resulting in lower emissions-related defects. The antibacterial activity was evaluated against four bacterial strains: Escherichia coli, Staphylococcus aureus, Pseudomonas aeruginosa, and Bacillus subtilis using the well diffusion method. ZnO:NiO nanocomposites demonstrate superior bactericidal activity compared to pure ZnO NPs against specific bacterial species due to their augmented surface area, reduced crystalline size, and elevated the formation of reactive oxygen species after following Ni2+ ion alteration.ZnO:NiO nanocomposites have the potential to serve as bactericidal agents that are resistant to harmful bacterial species due to their strong bactericidal activity. Antioxidant activity was assessed through DPPH free radical scavenging, superoxide anion scavenging, and ABTS radical cation scavenging assays. The results revealed that the ZnO nanocomposites exhibited strong antioxidant properties, indicating their potential to neutralize free radicals and reduce oxidative stress. [Graphical Abstract]