Green synthesis and characterization of zinc oxide nanoparticles using leaf extract of Thryallis glauca (Cav.) Kuntze and their role as antioxidant and antibacterial

The present work has reported a green chemistry-based approach for the synthesis of crystalline metal oxide nanoparticle using plant extract to reduce metal ions. It demonstrated the efficient synthesis of Zinc oxide nanoparticles (ZnO NPs) using aqueous leaf extract of Thryallis glauca (Cav.) Kuntze with a focus on minimizing toxic reactants and byproducts. The physicochemical characterizations by standard methods and the mechanism of action were presented. The UV-Vis absorption peak of the annealed ZnO NPs appeared at a 359 nm wavelength. The calculated direct band-gap energy was 3.6 eV. The peak at 567 nm in the visible region in the photoluminescence spectra indicated surface defects from oxygen vacancy, and the vibrational peak also indicated it at 582 cm-1 in Raman spectra. FTIR spectroscopy showed the possible involvement of proteins, aromatic compounds, and alcohols as reducing agents in the reaction. X-ray diffraction analysis revealed that pure crystalline ZnO NPs have structural properties as hexagonal wurtzite below 50 nm size. Antioxidant analysis by DPPH assay illustrated an excellent free radical scavenging activity. The prepared ZnO NPs tested against pathogenic Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus, and Bacillus subtilis did not show any antibacterial activity. HIGHLIGHTS: Renewable, eco-friendly plant material was used to synthesize Zinc Oxide nanoparticles (NPs). Synthesis of thermally stable, pure crystalline NPs with good optical properties. The synthesized NPs showed excellent free radical scavenging activity. ZnO NPs exhibited antibacterial resistance at the test concentrations.