Hydrothermal Growth of Manganese Dioxide into Three-Dimensional Hierarchical Nanoarchitectures

Novel three‐dimensional (3D) hierarchical nanoarchitectures of ϵ‐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 ϵ‐MnO2 dipyramidal single crystal axis and six secondary branches, which are arrays of single‐crystal ϵ‐MnO2 nanobelts. The growth directions of the nanobelts are perpendicular to the central dipyramidal axis, which shows sixfold symmetry. The shape of the ϵ‐MnO2 assembly can be controlled by the reaction temperature. The morphology of ϵ‐MnO2 changes from a six‐branched star‐like shape to a hexagonal dipyramidal morphology when the temperature is increased from 160 to 180 °C. A possible growth mechanism is proposed. The synthesized ϵ‐MnO2 shows both semiconducting and magnetic properties. These materials exhibit ferromagnetic behavior below 25 K and paramagnetic behavior above 25 K. The ϵ‐MnO2 system may have potential applications in areas such as fabrication of nanoscale spintronic materials, catalysis, and sensors. ϵ‐MnO2 with controlled 3D hierarchical nanoarchitectures (see Figure) has been synthesized through a simple hydrothermal process. The self‐organized crystals consist of a major ϵ‐MnO2 dipyramidal single crystal axis and secondary branches. The formation mechanism is investigated. The synthesized ϵ‐MnO2 shows both semiconducting and magnetic properties.