Green Innovation: Multifunctional Zinc Oxide Nanoparticles Synthesized Using Quercus robur for Photocatalytic Performance, Environmental, and Antimicrobial Applications

Abstract

This study investigates the green synthesis of zinc oxide nanoparticles (ZnO NPs) using leaf extract as a natural reducing agent, evaluating their antimicrobial and photocatalytic properties. The nanoparticles were annealed at 320 °C and 500 °C, and the effects of leaf extract concentration and annealing temperature on their structural, morphological, and electronic properties were systematically explored. X-ray diffraction (XRD) analysis confirmed the hexagonal wurtzite structure of ZnO, with crystallite size and defect density being influenced by the concentration of the extract. Scanning electron microscopy (SEM) revealed the formation of smaller, spherical particles, with increased aggregation observed at higher extract concentrations. Fourier-transform infrared spectroscopy (FTIR) identified key functional groups, such as hydroxyl groups, C–O bonds, and metal–oxygen vibrations. UV–Vis spectroscopy showed a reduction in band gap energy and an increase in Urbach energy as the extract concentration and annealing temperature were increased. The antimicrobial activity of the ZnO NPs was evaluated against Gram-positive and Gram-negative bacteria as well as Candida albicans, demonstrating significant antibacterial efficacy. Photocatalytic degradation studies of methylene blue dye revealed a superior efficiency of up to 74% for the annealed samples, particularly at 500 °C. This research highlights the potential of green-synthesized ZnO NPs for a wide range of applications, including antimicrobial agents, water purification, and environmental catalysis. It contributes to the advancement of sustainable nanotechnology, offering promising solutions for both technological and ecological challenges.