Green Synthesis and Antibacterial Activity of Zinc Oxide Nanoparticles Using Rosemary (<i>Salvia rosmarinus</i>) Extract

Background: Green synthesis by plants is a good alternative to conventional chemical methods, as it eliminates hazardous reagents and reduces environmental impacts. Objectives: This study aims to green synthesize zinc oxide nanoparticles (ZnO NPs) using rosemary as a natural reductant and stabilizer. Methods: The characterization of the biosynthesized ZnO NPs was conducted via UV-visible spectroscopy, Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), dynamic light scattering (DLS), zeta potential (ZP) analysis, scanning electron microscopy (SEM), and energy dispersive X-ray spectroscopy (EDX). The antibacterial activity was tested against both the representative gram-positive Staphylococcus aureus and gram-negative Escherichia coli bacteria. Results: The characterizations identified crystalline ZnO NPs with a hexagonal wurtzite structure and an average crystallite size of 46.14 nm. The DLS revealed a hydrodynamic size of 652.5 nm, coupled with a high negative ZP (-45.4 mV), indicating excellent colloidal stability. The FTIR and EDX results indicated phytochemical residues of rosemary on the surfaces of nanoparticles, thus confirming the dual role of the extract responsible for both reduction and capping. The SEM images revealed geometries ranging from spherical to hexagonally shaped and uniformly distributed, while EDX confirmed elemental purity. Conclusions: Plant-mediated green synthesis to fabricate functional zinc oxide (ZnO) nanomaterials with excellent antibacterial properties is feasible, as demonstrated in this work. The rosemary-mediated approach offers sustainable avenues for the application of antimicrobial therapy, biomedical devices, and environmental remediation. The dual functionality of rosemary extract as a reducing and stabilizing agent, coupled with synergistic antibacterial action, contributes to the advantages of green synthesis methods for nanotechnology applications.