National Centre for Nanoscience and Nanotechnology, University of Madras, Chennai - 600025, India.
Nanoscale. 2018 Jul 5;10(25):12018-12034. doi: 10.1039/c8nr03397h.
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.
通过一种改进的多元醇法制备了还原氧化石墨烯（rGO）-Fe3O4 的新型纳米复合材料，记为“rGO:IO”，以及氮掺杂 rGO-ε-Fe3N 的新型纳米复合材料，记为“NrGO:IN”，其中同时发生了石墨烯氧化物的还原和 Fe2+/Fe3+离子的氧化，随后进行了氨氮化。rGO:IO 和 NrGO:IN 纳米复合材料的电子显微镜分析显示出独特的形态。在 rGO:IO 中，发现平均直径为 38nm 的 Fe3O4 纳米颗粒均匀地锚定在 rGO 片表面上，而在 NrGO:IN 中，ε-Fe3N 纳米颗粒（约 150nm）被 NrGO 片屏蔽。rGO:IO 和 NrGO:IN 纳米复合材料分别表现出超顺磁性和弱铁磁性特征，饱和磁化强度值分别为 39.5 和 46 emu g-1，这可归因于组成磁性纳米颗粒 Fe3O4 和 ε-Fe3N 的性质。此外，石墨烯衍生物如 rGO 和 NrGO 有助于提高纳米复合材料的电性能。电化学阻抗谱分析表明，与纯 Fe3O4 和 ε-Fe3N 纳米颗粒相比，当与 rGO 和 NrGO 片结合时，rGO:IO 和 NrGO:IN 的总电阻分别降低了 33344.8 和 1569.87 Ω cm-2。此外，首次研究了 NrGO:IN 纳米复合材料的电磁屏蔽性能，并与其他样品进行了比较。在所制备的两种纳米复合材料中，NrGO:IN 在 11.4GHz 时表现出 35.33dB 的电磁屏蔽效能，明显大于 rGO:IO（在 8GHz 时为 14.4dB）。这种增强的屏蔽效果不仅归因于 ε-Fe3N 纳米颗粒固有的高磁电性能，还归因于 NrGO:IN 的“颗粒屏蔽片”形态，这种形态增强了 NrGO 片/ε-Fe3N 纳米颗粒异质界面处的电荷积累。
