Synthesis of Co₃O₄ Spinel at Ambient Conditions

Co₃O₄ was prepared in aqueous solutions through a staged oxidation process. When the mole ratio of starting chemicals Co²⁺:OH⁻ is ≤1:2 (Co²⁺ as a limiting reagent), the formation reaction follows the brucitelike phase to cobalt oxide-hydroxide, and then to cubic spinel. However, when the ratio of Co²⁺:OH⁻ is > 1:2 (OH⁻ as a limiting reagent), the reaction path changes to the brucite-like to hydrotalcite-like phase, and then to the spinel. Using the present method, Co₃O₄ can be formed at a temperature as low as 40 °C, and single-phase spinel Co₃O₄ can be prepared at 50 °C within hours under normal atmospheric pressure.