Morphology-Controlled Synthesis and Novel Microwave Absorption Properties of Hollow Urchinlike α-MnO2 Nanostructures

Three types of hollow urchinlike alpha-MnO2 nanostructures, namely, columnar nanorod clusters, tetragonal nanotube clusters, and tetragonal nanorod clusters, have been synthesized through a facile hydrothermal method. The microstructure and morphologies of the resulting materials were investigated by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and selected-area electron diffraction, and the microwave absorption properties of these nanostructures were investigated in terms of complex permittivity and permeability. The results indicate an obvious magnetic loss in the manganese oxide/paraffin wax composites. The tetragonal nanorod clusters exhibit enhanced microwave absorption properties compared with columnar nanorod clusters and tetragonal nanotube clusters, which result from proper electromagnetic impedance matching. These urchinlike manganese oxide nanostructures are considered to have great potential applications as microwave absorbents.