Shape‐controlled Synthesis of Nanostructure Ramsdellite‐type Manganese Oxide at Atmospheric Pressure

Abstract

AbstractRamsdellite (R‐MnO2) was prepared by oxidizing bivalent manganese salts, such as MnCl2, MnSO4 and Mn(NO3)2, with NaClO solution using a refluxing process at atmospheric pressure. The products were characterized by X‐ray diffraction, fourier transform infrared spectroscopy, transmission electron microscopy, scanning electron microscopy and flame photometry. R‐MnO2 microstructure and morphology were controlled by adjusting reaction temperature, the amount of hydrochloric acid (HCl) and anions of bivalent manganese salts. Ramsdellite grain was formed with three different bivalent manganese salts oxidized by NaClO solution at 60°C, and increased with the increase of reflux temperature. R‐MnO2 nanorod and nanowire crystals were obtained when MnCl2 and MnSO4 were used as bivalent manganese salts at 100°C respectively. Nanosized flake of R‐MnO2 came into being when Mn(NO3)2 was applied at 80°C. When 30 mmol MnCl2 was oxidized by 60 mmol NaClO solution with adding 20 mmol HCl in refluxing solution, specific surface area of R‐MnO2 grain obtained at 60°C was greater than 140 m2/g, and the self‐assembly of nanorod bundles into interesting flowerlike architectures was achieved at 100°C. The process of dissolution‐precipitation equilibrium might be the primary cause for the morphology transformation.