Optimization and characterization of peanut shell extract mediated green synthesis of ZnO nanoparticles for enhanced antimicrobial and photocatalytic applications

Zinc oxide nanoparticles (ZnO NPs) were biosynthesized with aqueous peanut shell extract (PSE), an agro-waste-derived reducing and capping agent, offering a cost-efficient and eco-compatible substitute to conventional chemical synthesis routes. Response surface methodology (RSM) was used to optimize three key synthesis parameters, namely, temperature, pH, and extract-to-salt (E/S) ratio, with respect to the nanoparticle yield. Accordingly, a two-factor interaction (2FI) model was found to be the best for describing the process, and numerical optimization identified 79.4 °C, pH 8.95, and an E/S ratio of 1.81 as the optimal conditions, yielding 13.32 g of PSE-ZnO NPs. GC-MS profiling of the extract confirmed the presence of phenolic and flavonoid constituents, notably luteolin, which is responsible for bioreduction. The synthesized nanoparticles were characterized with UV-Vis spectroscopy, XRD, FESEM, TEM, EDX, FTIR, and zeta potential analysis. The PSE-ZnO NPs exhibited concentration-dependent antibacterial activity against Staphylococcus haemolyticus and Escherichia coli, alongside notable photocatalytic degradation of Rhodamine B dye, following pseudo-first-order kinetics, with hydroxyl radicals identified as the dominant reactive species. The NPs retained approximately 89% of their initial photocatalytic activity after five reuse cycles, demonstrating good operational stability. These findings establish peanut shell extract as an effective and sustainable biotemplate for producing multifunctional ZnO nanostructures with promising antimicrobial and environmental remediation applications.