Formation and conversion mechanisms between single-crystal gamma-MnOOH and manganese oxides

Formation and conversion mechanisms between single-crystal gamma-MnOOH and manganese oxides had investigated systematically. Without extra surfactant or template, α-MnO2 nanorods and prismatic single crystalline γ-MnOOH rods had been synthesized under hydrothermal treatment in this study. The formation and conversion mechanisms of prismatic γ-MnOOH rod were investigated by powder X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). It was found that the formation process includes three evolution stages: (1) formation of α-MnO2 nanorods whiskers; (2) transformation from α-MnO2 nanorods to prismatic γ-MnOOH rods by a dissolution-growth-recrystallization process; and (3) preferred growth on (1 1 1¯) crystal plane. In addition, β-MnO2, Mn2O3 or Mn3O4 rods could be obtained by calcination of the γ-MnOOH rods at different temperatures, which indicated that γ-MnOOH is an important precursor for preparing manganese oxides. The morphology and dimension of γ-MnOOH rods remained unchanged after converted to β-MnO2, Mn2O3 and Mn3O4.

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► Single-crystal γ-MnOOH was obtained via hydrothermal method.
► α-MnO2 was transformed to γ-MnOOH by a dissolution-growth-recrystallization process.
► α-MnO2 preferred growth on (1 1 1¯) crystal plane of γ-MnOOH.
► γ-MnOOH was a useful precursor to prepare manganese oxide via calcination.