Sub-30 nm Fe3O4 and γ-Fe2O3 octahedral particles: preparation and microwave absorption properties

A simple low-cost hydrothermal method has been developed to fabricate uniformly dispersed octahedral Fe3O4 nanoparticles with tunable size. The particle size can be reduced to 20–30 nm under the effect of phosphate, meanwhile, the edetate disodium can improve the dispersivity of particles. High-resolution transmission electron microscope showed that the octahedral Fe3O4 nanoparticle was enclosed by eight (111) planes. Octahedral γ-Fe2O3 nanoparticles were obtained by reoxidizing the as-synthesized Fe3O4 nanoparticles. The microwave absorption properties of the octahedral Fe3O4 and γ-Fe2O3 nanoparticles were measured in the frequency range of 2–18 GHz. A minimum reflection loss of −28 dB was observed at 8.6 GHz for octahedral Fe3O4 nanoparticles.