Sustainable synthesis of ZnO nanoparticles from melon (cucumis melo l.) by-products: RSM optimization, structural characterization, antioxidant activity, and photocatalytic performance

This study explores the eco-friendly synthesis of zinc oxide nanoparticles (ZnO-NPs) using polyphenol-rich extracts from melon (Cucumis melo L.) peel and seeds as naturalreducing and stabilizing agents. Optimization via response surface methodology (RSM) determined the ideal synthesis conditions at a 0.078 mol/L metal concentration, 14.73 mL extract, and pH 10.77. Characterization through XRD confirmed a hexagonal wurtzite crystal structure with an average size of 21.7 nm, while SEM and TEM imaging revealed predominantly spherical morphologies. UV–visible DRS analysis showed a 368 nm absorption edge with a calculated band gap of 3.21 eV. DLS measurements indicated a hydrodynamic diameter of 135.6 nm with a PDI of 0.206 and a zeta potential of −20.5 mV, confirming good colloidal stability. The resulting NPs exhibited strong antioxidant activity (IC50 = 40.7 µg/mL) and acted as effective heterogeneous photocatalysts for the degradation of organic dyes. Specifically, ZnO-NPs enabled the photodegradation of methyl orange (MO) and methylene blue (MB), achieving 63.56% degradation for 5 mg L−1 MO. These findings demonstrate that melon-waste-derived ZnO-NPs are sustainable and promising candidates for wastewater treatment and environmental remediation.