Green synthesis, characterization and antimicrobial activity of ZnO and Co-doped ZnO nanoparticles obtained using aqueous extracts of Platycladus orientalis leaves

This study investigates the synthesis, structural characteristics, and antimicrobial applications of zinc oxide (ZnO) and cobalt-doped ZnO (Co-doped ZnO) nanoparticles synthesized via a green method utilizing Platycladus orientalis aqueous extract. Comprehensive characterization techniques, including x-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), UV–vis spectroscopy, and Fourier transformed infra-red (FTIR) spectroscopy, were employed to evaluate the structural, morphological, and optical properties. XRD analysis confirmed the hexagonal wurtzite structure of ZnO with successful Co-doping, evidenced by lattice distortion and reduced crystallite size. The estimated crystallite size and lattice microstrain of the ZnO and Co-doped ZnO nanoparticles were 26.9 and 19.0 nm, and 0.16% and 0.2%, respectively. Furthermore, the lattice parameters showed a significant distortion of the lattice along the c-axis in the Co-doped ZnO nanoparticles. SEM and TEM revealed improved particle uniformity and decreased agglomeration in Co-doped ZnO nanoparticles. UV–Vis spectroscopy demonstrated a narrowing of the optical band gap, enhancing visible light absorption. Antimicrobial studies showed significant concentration-dependent activity, with Co-doped ZnO nanoparticles exhibiting superior antibacterial and antifungal properties compared to pristine ZnO. Co-doped ZnO demonstrated enhanced inhibition zones against Listeria monocytogenes (13.50 mm), Escherichia coli (13.65 mm), and Enterococcus faecalis (14.05 mm), and also showed better minimum inhibitory concentrations (MICs) against fungal strains such as Mucor mucedo (0.05 mg/mL), Penicillium chrysogenum (0.05 mg/mL), and Aspergillus niger (0.03 mg/mL). The superior antimicrobial performance is attributed to modifications in particle size, morphology, and lattice defects induced by cobalt doping. These findings highlight the potential of Co-doped ZnO nanoparticles as advanced antimicrobial agents, suitable for applications in biomedical fields.