One pot synthesis of Fe3O4/MnO2 core-shell structured nanocomposites and their application as microwave absorbers

Fe3O4/MnO2 core-shell structured nanocomposites have been synthesized by a one-pot approach at ambient temperature and pressure. The morphology of the prepared Fe3O4/MnO2 nanoparticles is governed by the Mn/Fe molar ratio in the precursor. When the molar ratio of Mn/Fe is 1 : 10, the nanocomposites exhibit a special microstructure, in which MnO2 nanorods are formed on the surface of spherical Fe3O4 nanoparticles. With the increase of the Mn/Fe ratio to 1 : 2, core-shell structured nanoparticles with Fe3O4 nanoparticles as cores and MnO2 as the shell are obtained. The microwave absorption properties of the core-shell Fe3O4/MnO2 nanocomposites were studied in the 2-18 GHz frequency range. The microwave absorption performance of the Fe3O4/MnO2 nanocomposites exhibited a remarkable enhancement in comparison with pure Fe3O4 nanoparticles, ascribed to the fact that MnO2 nanostructures can improve the dielectric loss factor and the electromagnetic (EM) matching degree. The absorption peaks of the Fe3O4/MnO2-paraffin composites are red shifted compared to those of Fe3O4-paraffin composites. Due to the MnO2 nanorods on the surface of the Fe3O4 nanoparticles, the produced microcurrent can reduce the electron transition energy and lead to better microwave absorption by the Fe3O4 nanoparticle/MnO2 nanorod nanocomposites.