A simple microplasma reactor paired with indirect ultrasonication for aqueous phase synthesis of cobalt oxide nanoparticles

Cobalt oxide nanoparticles are widely used owing to their distinct properties such as their larger surface area, enhanced reactivity, and their superior optical, electronic, and magnetic properties when compared to their bulk counterpart. The nanoparticles are preferably synthesized using a bottom-up approach in liquid as it allows the particle size to be more precisely controlled. In this study, we employed microplasma to synthesize Co 3 O 4 nanoparticles because it eliminates harmful reducing agents and is efficient and cost-effective. Microplasma reactors are equipped with copper wire electrodes to generate plasma and are simple to configure. The product was characterized using UV-Vis spectroscopy, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), field emission scanning electron microscopy (FESEM), and transmission electron microscopy (TEM). The experimental parameters that were varied for the synthesis were: with or without stirring, with or without indirect ultrasonication, and with or without capping agents (urea and sucrose). The results showed that the microplasma enabled Co 3 O 4 nanoparticles to be successfully synthesized, with particle sizes of 10.9-17.7 nm, depending on the synthesis conditions. The use of microplasma to synthesize Co 3 O 4 nanoparticles is a novel approach that eliminates the need for harmful reducing agents.