Green Synthesis of Copper Oxide Nanoparticles Using Citrus sinensis Leaves: Effects of Experimental Parameters, Antimicrobial Evaluation and Development of Chitosan Composites

Copper oxide nanoparticles (CuONPs) have received considerable attention because of their wide range of applications, particularly in the development of antimicrobial materials for medical, environmental, and industrial purposes. However, conventional synthesis routes often involve the use of toxic chemicals and environmentally harmful conditions. To overcome these limitations, green synthesis strategies have been developed as sustainable alternatives through the use of natural reducing and stabilizing agents. In this study, <i>Citrus sinensis</i> leaf extract, which exhibits high antioxidant capacity, was investigated for green synthesis of CuONPs, followed by their subsequent incorporation into a chitosan polymeric matrix. The optimal synthesis conditions were achieved at a pH of 7.0 using copper(II) acetate monohydrate (Cu(CH₃COO)₂·H₂O) at a concentration of 10.0 g L^-1 and a calcination temperature of 300 °C. The resulting CuONPs exhibited a heterogeneous morphology, with average particle sizes ranging from 20 to 30 nm, and demonstrated satisfactory antimicrobial activity against <i>Escherichia coli</i> and <i>Staphylococcus aureus</i>. The incorporation of these NPs into chitosan yielded composite materials with enhanced antimicrobial performance, highlighting the added value of polymer-NP hybrid systems. Although these composite materials were not evaluated under realistic operational conditions, the optimized green protocol provides a robust methodological basis for future studies targeting water disinfection and other environmentally relevant technologies.