Green synthesis, characterization, and antibacterial efficiency of copper oxide nanoparticles using Mitragyna speciosa (Korth.) Havil leaf extract

Copper oxide nanoparticles (CuO NPs) possess versatile properties that make them valuable in various applications, including electronics, catalysis, sensing, and biomedical fields. However, conventional synthesis routes often require high energy input, hazardous chemicals, and generate environmentally problematic byproducts. In this work, CuO NPs were synthesized through an eco-friendly green method using Mitragyna speciosa (Korth.) Havil leaf extract, whose phytochemicals function as natural reducing and stabilizing agents. The nanoparticles were characterized using UV–visible spectroscopy, FESEM–EDS, and XRD. The optical spectrum exhibited an absorption maximum at $\sim$480 nm, and the corrected Tauc analysis yielded an indirect band gap of 1.57 eV. XRD analysis confirmed the formation of monoclinic CuO with crystallite sizes of 82--98 nm (Scherrer and Williamson–Hall methods), consistent with FESEM particle sizes of 50--80 nm. Antibacterial tests revealed activity against both Escherichia coli and Staphylococcus aureus, with minimum inhibitory concentrations (MICs) of 3.98 $\times$ 10$^{4}$ $\mu$g/mL and 1.00 $\times$ 10$^{5}$ $\mu$g/mL, respectively. These results demonstrate that M. speciosa-mediated synthesis offers a viable, cost-effective, and sustainable approach for producing functional CuO nanoparticles, thereby supporting their potential in future environmental and biomedical applications.