Synthesis of CoO and Co ₃O ₄ nanoparticles by salt-assisted combustion method

In the present study, CoO, which is hard to synthesize because of the chemical activity of cobalt metal, and the popular Co ₃O ₄ have been successfully controlled produced by a salt-assisted combustion method (SACM), in which Co(NO ₃) ₂·6H ₂O, polyethylene glycol (PEG2000) were chosen as oxidant and fuel respectively. The CoO and Co ₃O ₄ nanoparticles were investigated by high resolution transmission electron microscopy (HRTEM), selected area electron diffraction (SAED), x-ray diffraction (XRD), simultaneous thermogravimetric and differential thermal analysis (TG-DTA) and N ₂ adsorption. It is found that the pure CoO were obtained whatever adjusting the weight ratio of Co(NO ₃) ₂·6H ₂O and PEG2000 in the absence of inert salt. While, well-dispersed Co ₃O ₄ nanoparticles with a high specific surface area were successfully obtained with the introduction of NaCl or KCl in the system, which results from the fact that the introduction of inert inorganic salt as a agglomeration inhibitor into the redox mixture precursor led to the breakup of fractal nanocrystallite agglomerates. A mechanism was proposed to illustrate the possible formation processes and the role of the inert inorganic salt.