Enhanced shielding effectiveness in nanohybrids of graphene derivatives with Fe3O4 and ε-Fe3N in the X-band microwave region

Abstract

Novel nanocomposites of reduced graphene oxide (rGO)–Fe₃O₄, denoted as ‘rGO:IO, and nitrogen doped rGO–ε-Fe₃N, denoted as ‘NrGO:IN’, were prepared by a modified polyol method, wherein both the reduction of graphene oxide and oxidation of Fe²⁺/Fe³⁺ ions occurred simultaneously, followed by ammonia nitridation. The electron microscopy analysis of the rGO:IO and NrGO:IN nanocomposites revealed unique morphologies. In rGO:IO, the Fe₃O₄ nanoparticles having a mean diameter of 38 nm were found to be uniformly anchored to the rGO sheet surface, whereas in NrGO:IN, the ε-Fe₃N nanoparticles (∼150 nm) were shielded by the NrGO sheets. Superparamagnetic and weak ferromagnetic characteristics with saturation magnetization values of 39.5 and 46 emu g⁻¹ were observed in the rGO:IO and NrGO:IN nanocomposites respectively, which can be attributed to the nature of the constituent magnetic nanoparticles, Fe₃O₄ and ε-Fe₃N. In addition, the graphene derivatives such as rGO and NrGO contributed to the enhanced electrical properties of the nanocomposite. The electrochemical impedance spectroscopy analysis showed that, compared to pure Fe₃O₄ and ε-Fe₃N nanoparticles, the total electrical resistance of rGO:IO and NrGO:IN was reduced by 33 344.8 and 1569.87 Ω cm⁻², respectively, when combined with the rGO and NrGO sheets. Further, the electromagnetic shielding performance of the NrGO:IN nanocomposite was investigated for the first time and was compared with the other samples. Of the two prepared nanocomposites, NrGO:IN exhibited electromagnetic shielding effectiveness of 35.33 dB at 11.4 GHz, which is considerably larger than that of rGO:IO (14.4 dB at 8 GHz). This enhanced shielding effectiveness is not only due to the high inherent magnetic and electrical properties of ε-Fe₃N nanoparticles, but also due to the ‘particle shielded by sheet’ morphology of the NrGO:IN, which enhances the charge accumulation at the heterogeneous interfaces of NrGO sheets/ε-Fe₃N nanoparticles.