Synthesis of Crystalline Copper Oxide (CuO) Nanoparticles via a Combined Polyol and Thermal Decomposition in Air

Copper(II) oxide (CuO) nanoparticles are of growing interest due to their versatility in catalysis, energy storage, and environmental remediation. In this work, a novel air-assisted polyol-thermal decomposition method was developed to synthesize crystalline CuO nanoparticles with a controlled size. The reaction used copper(II) acetate in 1,4-butanediol at 140 °C under varying airflow conditions and reaction times, followed by calcination at 400 °C in air. Continuous air bubbling minimized the formation of Cu₂O and metallic Cu, while maximizing the CuO yield with shortened reaction times. The optimal conditions involved a 4 h polyol reaction while purging air at 1800 cm³/min, followed by 4 h of calcination. This method resulted in polycrystalline monoclinic CuO nanoparticles with a size of 73 ± 32 nm, as observed by TEM and XRD. FT-IR and Raman spectroscopy verified the compositional purity of the nanoparticles. To enhance colloidal stability, a citrate coating reaction of CuO was optimized using sodium citrate dihydrate or citric acid in either water or 1,4-butanediol. The optimal coating conditions employed sodium citrate in water with bath sonication and overhead stirring, yielding a zeta potential of -40.6 ± 0.4 mV at pH 7. This work provides a practical and tunable method for producing high-quality CuO nanoparticles suitable for diverse applications.