Enhanced microwave absorption property of bowl-like Fe3O4 hollow spheres/reduced graphene oxide composites

Abstract

A novel kind of Fe₃O₄ hollow spheres/reduced graphene oxide (r-GO) composites has been synthesized by a facile solvothermal method. The scanning electron microscopy and transmission electron microscopy images show bowl-like Fe₃O₄ hollow spheres with an average outer diameter of 395 nm and a shell thickness of 100 nm decorating on the both sides of r-GO sheets. The co-existence of both D and G peaks in Raman spectra confirms the presence of r-GO state, and an increased D/G intensity ratio of the composites suggests a substantial increase in disorder degree in the r-GO sheets due to the Fe₃O₄ hollow spheres anchoring on the surface. Compared to pristine r-GO, pure Fe₃O₄ nanoparticles, and the reported solid nano-Fe₃O₄/r-GO, both a wider and stronger absorption have been achieved in the frequency range of 2–18 GHz. In particular, the sample containing 30 wt. % as-synthesized hollow Fe₃O₄/r-GO with a coating layer thickness of 2.0 mm exhibits a maximum absorption of 24 dB at 12.9 GHz as well as a bandwidth of 4.9 GHz (from frequency of 10.8–15.7 GHz) corresponding to reflection loss at −10 dB. The measured complex relative permittivity and permeability data reveal that the enhanced microwave properties are contributed by a major improved dielectric loss and a minor magnetic loss resulting from the incorporation of hollow Fe₃O₄ on r-GO.