Abstract
This study reports the green synthesis of zinc oxide nanoparticles (ZnO NPs) using an aqueous leaf extract of Senecio angulatus as a reducing and stabilizing agent, and evaluates how calcination temperature influences their physicochemical characteristics and biological activities. The biosynthesized NPs were calcined at 400, 450, and 500 °C and designated as ZnO(400), ZnO(450), and ZnO(500), respectively. X-ray diffraction confirmed the formation of phase-pure hexagonal wurtzite ZnO with average crystallite sizes of 26.9, 24.0, and 28.9 nm for the ZnO(400), ZnO(450), and ZnO(500), respectively. Fourier transform infrared spectroscopy spectra confirmed the presence of metal-oxygen vibrations associated with Zn–O bond formation (644–646 cm−1), while the UV–Vis spectroscopy showed absorption maxima between 369 and 373 nm. Optical band-gap energies of 3.60, 3.40, and 3.30 eV were obtained for ZnO(400), ZnO(450), and ZnO(500), respectively. The antioxidant potential, determined by DPPH assay, increased with calcination temperature, with ZnO(500) exhibiting the lowest IC50 (21.02 µg ml−1), approaching the activity of the reference antioxidant, ascorbic acid (17.58 µg ml−1). Antibacterial evaluation against Escherichia coli, Staphylococcus aureus, and Listeria monocytogenes demonstrated concentration-dependent inhibition, with ZnO(450) and ZnO(500) showing greater activity than ZnO(400). Similarly, antifungal activity against Mucor sp and Penicillium sp improved with increasing calcination temperature, and ZnO(500) achieved minimum inhibitory concentrations of 0.03 and 0.04 mg ml−1, respectively, comparable to Amphotericin B (0.025 mg ml−1). These results demonstrate that calcination temperature is an important parameter governing the structural, optical, antioxidant, and antimicrobial properties of S. angulatus-derived ZnO nanoparticles, highlighting their potential as multifunctional nanomaterials for biomedical and food preservation applications.