Single-crystal growth of MnOOH and beta-MnO2 microrods at lower temperatures

Single-crystal MnOOH microrods were prepared hydrothermally by reducing KMnO4 with NH4Cl at 150 °C for 24 h. After the subsequent heat treatment of the as-prepared MnOOH microrods at 350 °C for 10 h in air, single-crystal beta-MnO2 microrods were obtained, which retained the similar morphologies of MnOOH microrods. The products were characterized by powder X-ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM), and transmission electron microscopy (TEM). The influences of different reductants, the molar ratio between reaction materials, and temperature on the morphology and phase of the final products under hydrothermal conditions are discussed. The reaction temperature and reductant NH4Cl were crucial factors for the formation and morphologies of MnOOH microrods. Based on the experimental results and MnOOH crystal structure, a possible formation mechanism has been proposed on the growth of MnOOH microrods.