Hydrothermal growth of manganese dioxide into three-dimensional hierarchical nanoarchitectures

Novel three-dimensional (3D) hierarchical nanoarchitectures of epsilon-MnO2 have been synthesized by a simple chemical route without the addition of any surfactants or organic templates. The self-organized crystals consist of a major epsilon-MnO2 dipyramidal single crystal axis and six secondary branches, which are arrays of single-crystal epsilon-MnO2 nanobelts. The growth directions of the nanobelts are perpendicular to the central dipyramidal axis, which shows sixfold symmetry. The shape Of the epsilon-MnO2 assembly can be controlled by the reaction temperature. The morphology of epsilon-MnO2 changes from a six-branched star-like shape to a hexagonal dipyramidal morphology when the temperature is increased from 160 to 180 degrees C. A possible growth mechanism is proposed. The synthesized epsilon-MnO2 Shows both semiconducting and magnetic properties. These materials exhibit ferromagnetic behavior below 25 K and paramagnetic behavior above 25 K. The epsilon-MnO2 system may have potential applications in areas such as fabrication of nanoscale spintronic materials, catalysis, and sensors.