Optimized wet-chemical synthesis of ultra-small CuO nanoparticles with high antibacterial activity

Copper oxide nanoparticles (CuO NPs) are attractive owing to their size- and shape-dependent properties, as well as their diverse applications. Therefore, the synthesis of environmentally friendly CuO NPs using low-toxicity reagents remains significant. In this study, a benign wet-chemical process was applied to synthesize CuO NPs in an alcohol-water mixture, employing copper acetate as the precursor and sodium oleate as the surfactant. Multiple experimental parameters, including water content, the molar ratio of sodium oleate to copper acetate, types of alcohols, and reaction temperature, were investigated to examine their effects on the formation and structures of the resulting products. Results from X-ray diffraction (XRD) and transmission electron microscopy (TEM) confirmed the monoclinic crystalline structure of CuO NPs with an ultra-small size of less than 3 nm. The size of CuO NPs can be easily adjusted by altering the water content, the molar ratio of precursor to surfactant, and other factors. The as-synthesized CuO NPs exhibited significantly enhanced antibacterial activity against Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus).