Effect of Hydrothermal Time, pH, and Alkali on Crystal Phase and Morphology of Manganese Oxides

γ‐MnOOH nanowires and Mn₃O₄ nanoparticles were prepared in the hydrothermal process. The effect of hydrothermal time, pH, and alkali on morphology and composition of manganese oxides was investigated. The results of XRD, TEM, and SEM showed that the γ‐MnOOH prepared in shorter hydrothermal time was a mixture of nanocubes and nanowires, while in longer hydrothermal time was pure nanowires. Interestingly, increasing the pH of the reaction system from 8 to 10, the mixture of γ‐MnOOH nanowires and Mn₃O₄ nanoparticles was obtained. Alkali types also were discussed in directing the reaction and crystallization of manganese oxides. The product was pure γ‐MnOOH when using NaOH in the system, but a mixture of Mn₃O₄ and γ‐MnOOH was obtained when using NH₃ · H₂O.

Keywords:

• Manganese oxides
• hydrothermal treatment
• crystal phase
• morphology

This work was supported by Excellent Young Teacher Program and Research Foundation of Returning Student Abroad, MOE of China. We thank the Shanghai Education Committee for support.