Modulating the Hydrothermal Synthesis of Co₃O₄ and CoOOH Nanoparticles by H₂O₂ Concentration

The formation process and product control are very important in material synthesis. In this study, a facile one-pot hydrothermal method was used to prepare Co₃O₄ and CoOOH. H₂O₂ was used to modulate the formation process and control the final product by changing its concentration. The crystalline structures and morphologies of the as-prepared products were characterized by X-ray diffraction (XRD), Raman spectra, and scanning electron microscopy (SEM) techniques. It was found that the concentration of H₂O₂ influenced not only the phase of the final products but also their morphologies. The influences of H₂O₂ concentration on the precursor formation and the reaction path have been revealed. At a low concentration of H₂O₂ (5 wt %), the formed precursor is Co(CO₃)_0.5(OH)·0.11H₂O, which can be directly transformed into Co₃O₄ upon increasing the hydrothermal time. At a medium concentration (15-20 wt %), the formed precursor and the final product are all CoOOH. At a high concentration (30 wt %), the formed precursor is CoOOH, and the final product is Co₃O₄. H₂O₂ plays the role of oxidant agent at the initial stage or reducing agent at the subsequent stage. This study offers a H₂O₂-concentration modulating method for the formation of Co₃O₄ and CoOOH.