The graphene-based electromagnetic wave absorption materials have attracted extensive attention due to their lightweight, strong absorption, broadband, and thin thickness. In this work, graphene hollow microspheres anchored with FeNi-coupled nanocrystal (GHMs@FeNi3/NiFe2O4) were synthesized using water-in-oil (W/O) emulsification and high-temperature calcination. The GHMs@FeNi3/NiFe2O4 microspheres have a homogeneous spherical morphology and a pronounced hollow structure, and the FeNi-coupled nanocrystals are homogeneously embedded in a spongy shell assembled by rGO nanosheets. Owing to the optimized impedance matching and enhanced attenuation, the GHMs@FeNi3/NiFe2O4 composites exhibit outstanding microwave absorption ability, particularly in the Ku band. The minimum reflection loss (RLmin) value can reach −58.96 dB at 14.43 GHz with a matching thickness of 2.25 mm, and the effective absorption bandwidth (lower than −10 dB) is up to 6.29 GHz (11.71–18 GHz) covering the whole Ku band. We believe that our work provides an idea for the design of high-performance absorbing composite materials.

The rational synergy of chemical composition and spatial nanostructures plays an important role in high-performance electromagnetic wave (EMW) absorption materials. Here, reduced graphene oxide (RGO) hollow microspheres loaded with CoNi alloy nanoparticles (Air@RGO/CoNi) were constructed by a facile water-in-oil emulsification route followed by high-temperature thermal treatment. The crystal structure, composition, microstructure, and magnetic properties of Air@RGO/CoNi were characterized by XRD, XPS, TEM, and VSM, respectively. The results demonstrated that the as-obtained Air@RGO/CoNi composites showed a uniform spherical morphology with a remarkably hollow structure. Impressively, nano-CoNi particles were compactly and uniformly distributed on the surface of RGO. Benefiting from the unique structure and compositional merits, the optimized Air@RGO/CoNi hollow microspheres exhibit superior (EMW) absorption performance. The minimum reflection loss (RLmin) value reached up to −56.16 dB at 13.67 GHz with a thin thickness of 2.55 mm and the widest effective absorption bandwidth (RL values are below −10 dB) covered 8.65 GHz (9.15–17.8 GHz) with a thinner thickness of 2.4 mm. Furthermore, possible EMW attenuation mechanisms had been proposed. Given these outstanding findings, we believe the as-fabricated Air@RGO/CoNi hollow microspheres can be promising candidates as highly microwave absorption materials with thin thickness, wide absorption bandwidth, and high absorption capacity.

A kind of reduced graphene oxide hollow microspheres loaded with FeCo alloy (AirRGO@FeCo) was synthesized by oil-in-water emulsification technology and high-temperature calcination process. By controlling the concentration of GO aqueous solution, five kinds of hollow microspheres with different RGO contents were synthesized. The diameter of the synthesized hollow microspheres was 4–6 μm, and the thickness of the spherical wall was 0.1–1 μm adjustable. As the concentration of GO aqueous solution is 6 mg/ml, the AirRGO@FeCo exhibits excellent electromagnetic wave absorption properties with an optimal reflection loss value reaching up to − 73.47 dB at 13.75 GHz and a broad effective bandwidth (lower than − 10 dB) of 7.23 GHz (10.77 to 18 GHz) at a thickness of 2.4 mm. The synergistic effects of dielectric loss and magnetic loss mechanisms as well as excellent impedance matching characteristics and strong attenuation characteristics make AirRGO@FeCo hollow microspheres obtain high efficient microwave absorption capacity.

静电纺丝技术是一种新颖、高效且简单的制备连续纳米纤维的方法,纳米复合纤维膜的优异特点赋予了纳米吸波剂新的吸波通道.本文采用静电纺丝工艺制备Fe3O4/PEK-C纳米复合纤维膜,利用SEM和TGA表征纳米复合纤维膜的微观形貌和热稳定性,用矢量网络分析仪测试样品在8.2-12.4 GHz的电磁参数与吸波性能.结果表明,Fe3O4/PEK-C纳米复合纤维膜呈现出超细纤维彼此交织构成的立体网络结构,其热稳定性、复介电常数和复磁导率均随着Fe3O4含量的增加而增加,介电损耗和磁损耗得到加强.当纳米复合纤维膜的厚度为1.8 mm时,其反射损耗在整个测试波段均处于-5 dB以下,-10 dB以下有效吸收频宽为2 GHz,频率在8.6 GHz处吸收强度达到最大值-15.4 dB.预期可作为隐身复合材料的吸波功能层.

In this study, the Ni/rGO hollow microspheres were synthesized and combined with epoxy foam to prepare structural absorbing materials. The diameter of obtained rGO hollow microspheres loaded with Ni nanoparticles was around 10 μm and the thickness of the spherical wall was about 70 nm. The Ni/rGO/EP composite foam exhibited better microwave absorption properties than that of rGO/EP and Ni/EP composite foam. The minimum reflection loss value (RLmin) could reach −58.23 dB at 8.4 GHz with a thickness of 2.5 mm, and the effective bandwidth with RLmin lower than −10 dB is 2.21 GHz ranging from 7.46 to 9.67 GHz. The porous structure of Ni/rGO hollow microspheres and their filled epoxy foam can refract and absorb the electromagnetic waves repeatedly, which equals to extend the propagation path of microwave, thus, electromagnetic loss capacity was improved obviously.

This paper reports a facile one-step reaction method to prepare rGo/Co hybrids with super-tiny Co nanocrystals coating on reduced graphene oxide, the rGo/Co hybrids have excellent electromagnetic wave absorption ability because of its good impedance matching and attenuation properties. The crystal structure, microtopography, and magnetic property of rGOs/Co hybrids were characterized by X-ray diffraction, transmission electron microscope, and vibrating sample magnetometer, respectively. Electromagnetic parameters were measured by vector network analyzer in the frequency range of 1–18 GHz using a coaxial line method. The rGOs can serve as perfect supports for dense coating of Co nanocrystals with an average size of 3.87 nm. Compared with pure rGOs and Co NPs, the rGO/Co hybrids exhibit excellent electromagnetic wave absorption properties with an optimal reflection loss (RL) value reaching up to − 52.73 dB at 14.34 GHz and a broad effective bandwidth (RL values lower than − 10 dB) of 6.2 GHz (11.8 to 18 GHz) at a thin thickness of 2.1 mm only. This work provides an efficient process to prepare a micro-nano composite absorber with strong and broadband electromagnetic wave absorption.

This paper reports a facile strategy for one-step synthesis of graphene anchored with super-tiny (< 5 nm) nickel nanoparticles (graphene@Ni) with high perfomance microwave absorption. The phase structure, morphology and magnetism of graphene@Ni were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM) and vibrating sample magnetometer (VSM), respectively. The magnetic Ni nanoparticles with 2.45 nm in average size are densely anchored on the surface of graphene. The electromagnetic characteristics of graphene@Ni compounds were measured by vector network analyzer using a coaxial line method in the frequency range of 1–18 GHz. The reflection loss (RL) of graphene@Ni reaches − 53.92 dB at 9.5 GHz with a thickness of 2.8 mm, and the maximum effective absorption bandwidth with RL values lower than − 10 dB is 5.44 GHz covering from 11.45 to 16.89 GHz at a thickness of 2.1 mm, showing that both of the RLmin and absorption bandwidth for graphene@Ni are obviously enhanced with thinner thickness compared to pure Ni NPs and graphenes. The real RL of graphene@Ni modified aramid fabrics/bismaleimide composite laminate is also measured for comparison, which is basically consistent with simulated results of graphene@Ni. Therefore, the graphene@Ni compounds have advantage in practice for high performance microwave absorption applications.

The efficient preparation of electromagnetic wave absorbing materials with low density and excellent electromagnetic wave absorption remains a considerable challenge. In this study, reduced graphene oxide (RGO) wrapped Fe3O4 nanoparticles (NPs) were synthesized based on one-step reaction by the reduction of graphene oxide (GO), and the generation of super-fine Fe3O4 NPs was achieved. The phase structure, chemical composition, micromorphology, and magnetism were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscope (XPS), scanning electron microscope (SEM), transmission electron microscope (TEM), and vibrating sample magnetometer (VSM), respectively. The electromagnetic characteristics were evaluated on a vector network analyzer by the coaxial line method. The results showed that super-fine Fe3O4 NPs with an average size of 6.18 nm are densely distributed on the surface of graphenes. The RGO/Fe3O4 nanocomposites exhibited excellent microwave absorption properties with a minimum reflection loss (RL) of up to −55.71 dB at 6.78 GHz at 3.5 mm thickness and the highest effective absorption bandwidth with RL values exceeding −10 dB is 4.76 GHz between 13.24 and 18 GHz at 1.7 mm thickness. This work provides a concise method for the development of RGO supported super dense Fe3O4 nanocomposites for high performance electromagnetic absorption applications.