Synthesis of Cobalt Oxide Nanoparticles Through Chemical and Biological Pathways for Antibacterial Activity

Green synthesis of nanoparticles (NPs) using different parts of plant extracts is a novel and environmentally benign method that can be used in numerous biomedical applications. In this study, cobalt oxide nanoparticles were synthesized through biological method using 0.2 M cobalt nitrate hexahydrate as a precursor salt and leaf extract of indigenous plant of Ethiopia called Phytolacca dodecandra as a reducing and capping agent. In addition to this, cobalt oxide nanoparticles were synthesized chemically by co-precipitation method from cobalt nitrate hexahydrate in the presence of sodium hydroxide as a precipitating agent. The synthesized Co3O4 NPs were characterized using X-Ray diffraction (XRD), scanning electron microscopy (SEM) coupled with energy dispersive spectroscopy (EDX), Ultraviolet-Diffuse Reflectance spectroscopy (UV-Vis-DRS) and Fourier transform infrared (FT-IR) spectroscopy. The average crystal size Co3O NPs were found to be 10.79 nm and 11.9 nm, having band gap energy of 3.35 eV and 3.18 eV for the biologically and chemically synthesized Co3O4 NPs, respectively. The shape and morphology of Co3O4 NPs synthesized in the two methods were found to be spherical. XRD and FT-IR analyses have confirmed the formation of Co3O4 NPs from its precursor salt in the presence of Phytolacca dodecandra leaf extract. The antibacterial activity of both the calcined and un-calcined biologically and chemically synthesized Co3O4 NPs were found in the range of 8.3-12.5 mm. As compared to the chemically synthesized Co3O4 NPs, biologically synthesized Co3O4 NPs shows high antibacterial activity due to the production of high reduced reactive oxygen species (ROS) because of the presence of Phytolacca dodecandra leaf extract and due to the relatively small average crystalline size as compared to chemically synthesized Co3O4 NPs.