Nanorods of manganese oxides: Synthesis, characterization and catalytic application

Single-crystalline nanorods of β-MnO₂, α-Mn₂O₃ and Mn₃O₄ were successfully synthesized via the heat-treatment of γ-MnOOH nanorods, which were prepared through a hydrothermal method in advance. The calcination process of γ-MnOOH nanorods was studied with the help of Thermogravimetric analysis and X-ray powder diffraction. When the calcinations were conducted in air from 250 to 1050 °C, the precursor γ-MnOOH was first changed to β-MnO₂, then to α-Mn₂O₃ and finally to Mn₃O₄. When calcined in N₂ atmosphere, γ-MnOOH was directly converted into Mn₃O₄ at as low as 500 °C. Transmission electron microscopy (TEM) and high-resolution TEM were also used to characterize the products. The obtained manganese oxides maintain the one-dimensional morphology similar to the precursor γ-MnOOH nanorods. Further experiments show that the as-prepared manganese oxide nanorods have catalytic effect on the oxidation and decomposition of the methylene blue (MB) dye with H₂O₂.