| Electromagnetic interference problems caused by electromagnetic radiation have become increasingly serious,with the rapid development and application of the electronic equipment in many fields such as the commerce,industry,medical and military.Therefore,microwave absorber possessing strong absorption ability has attracted wide attention.In recent years,researchers have done a lot of theoretical and experimental researches,hoping to get a microwave absorbing material which possesses such the characteristics as thin coating,low density,wide absorption band,strong absorption ability.A single type of absorbing material is difficult to meet this requirement,and therefore composite absorbing material has gradually become an important direction of the research.Graphene has unique two-dimensional structures,hexagonal honeycomb lattice of thin film which is composed of carbon atoms with sp~2 hybrid orbits.Graphene has good conductivity,excellent mechanical properties,high chemical stability,high specific surface area,etc.Graphene can attract abundant functional groups such as–OH and-C=O on its surface,so that other functional materials can be deposited or grown on the surface very well.Graphene could be used as a light quality of microwave absorbing materials because of its light quality and large surface area.However,for its high conductivity,its application in this respect could be limited.Therefore,researchers make nanometer materials which have dielectric loss or magnetic loss features deposited on the graphene to fabricate graphene nanocomposites,which greatly improve the application of graphene in absorbing materials.In this paper,four kinds of graphene nanocomposites have been synthesized on the basis of graphene.The synthesis methods of nanometer composite and nanomaterial's growth mechanism on the graphene have been studied.The microwave absorbing performance of the nanocomposites has been discussed.The morphology and structure of as-synthesis nanocomposite have been characterized by using SEM,TEM,XRD,XPS technology,etc.The electromagnetic parameters of materials are determined by the vector network analyzer.The main research contents and research results of this paper are as follows:This paper presents for the first time a successful synthesis of quaternary nanocomposites consisting of graphene,Fe3O4@Fe core/shell nanopariticles,and ZnO nanoparticles.Transmission electron microscopy measurements show that the diameter of the Fe3O4@Fe core/shell nanoparitcles is about 18 nm,the Fe3O4 shell's thickness is about 5 nm,and the diameter of ZnO nanoparticles is in range of 2–10 nm.The measured electromagnetic parameters show that the absorption band width with reflection loss less than–20 dB is up to7.3 GHz,and in the band range more than 99%of electromagnetic wave energy is attenuated.Moreover,the addition amount of the nanocomposites in the matrix is only 20 wt%.Therefore,the excellent electromagnetic absorption properties with lightweight and wide absorption frequency band are realized by the nanocomposites.We developed a new strategy----a seed-assistant method to fabricate three-dimensional(3D)SiO2@Fe3O4 core/shell nanorod array/graphene architecture.Scanning electron microscope and transmission electron microscope measurements showed that the SiO2@Fe3O4 core/shell nanorods with the length and the diameter of about 60 and 25 nm,respectively,were almost perpendicularly growing on both sides of surfaces of graphene sheets.The measured electromagnetic parameters showed that the 3D architecture exhibited excellent electromagnetic wave absorption property,i.e.,more than 99%of electromagnetic wave energy could be attenuated by the 3D architecture with an additional amount of only 20wt%in the paraffin matrix.In addition,the growth mechanism of the 3D architecture was proposed,and thus,the strategy presented here could be expended as a typical method to synthesize other 3D magnetic graphene nanostructures for extending their application areas.We developed a seed-assisted method to grow ultra-thin?-Fe2O3 nanosheets with aparamagnetic property on the surfaces of the graphene sheets.The scanning electron microscope and the transmission electron microscope measurements showed that the length,the height and the thickness of the nanosheets were about 140,120 and 5 nm,respectively.The measured electromagnetic parameters indicated that the three-dimensional(3D)graphene/?-Fe2O3 nanosheet arrays exhibited significantly enhanced electromagnetic wave absorption property compared to that of the graphene sheets and some magnetic nanomaterials.The minimal reflection loss was less than–15.2 dB for 3D graphene/?-Fe2O3nanosheet arrays with the thicknesses of 2 mm,and it was up to-64.1 dB when the thickness was 4.92 mm.The good electromagnetic wave absorption properties of the 3D graphene/?-Fe2O3 nanosheet arrays indicate that they are very promising for applicaton in electromagnetic wave absorbing field.We use a low temperature liquid phase synthesis method to grow FeNi alloy on the surface of graphene sheets.As TEM images can be seen,the tiny FeNi nanoparticles dispersed uniformly on the surface of graphene and the average particle size is less than 10nm.We acquired the G/FeNi nanocomposites possessing these features such as ultra-thin,ultra-light and the excellent electromagnetic absorption properties as a result of synergy effects of graphene and the metal alloys.The minimum RL value of G/FeNi nanocomposites almost reached-40 dB when d=0.45 mm.The RL value is lower than-20 dB at the range of12~17.5 GHz when the coating thickness is less than 1 mm.But this also states that the microwave absorption efficiency reaches over 99%at the bandwidth of 5.5 GHz,while the addition amount of G/FeNi nanocomposites in paraffin wax matrix is only 20 wt%.Compared with the G/Ni and G/Fe nanocomposites,G/FeNi nanocomposites have better absorbing performance.In conclusion,in order to obtain an absorbing material which has“thin,light,wide and strong"features,in this paper graphene nanocomposites have controllably synthesized by adopting simple and feasible methods.The as-synthesized nanocomposites have showed stronger electromagnetic absorption characteristics.Research work of this paper not only provides new thoughts for the design of new materials synthesis method,but also lays the foundation on theory research for graphene nanocomposite application in the field of microwave absorbing... |
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