Facile synthesis of γ-MnOOH micro/nanorods and their conversion to β-MnO2, Mn3O4

In the absence of extra surfactant or template, large-scale single-crystalline γ-MnOOH micro/nanorods were prepared directly via a hydrothermal method using Mn(NO3)2 aqueous solution as starting materials at 180 °C for 12 h. MnO2 could be obtained after calcining the γ-MnOOH precursor in air at 280 °C for 5 h and Mn3O4 could be synthesized via solvothermal treatment of γ-MnOOH in propylene glycol at 180 °C for 24 h. The products were characterized by powder X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectrometer, field-emission scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM). It was found that the MnO2 and Mn3O4 products were both single crystalline and retained the similar morphologies of MnOOH micro/nanorods. Further experiments showed that the as-prepared MnO2 and Mn3O4 micro/nanorods had catalytic effect on the oxidation and decomposition of the methylene blue dye with the assistance of hydrogen peroxide.