Synthesis And Microwave Absorption Performance Of Three-dimensional Graphene-based Nanocomposites

Electromagnetic (EM) interference problems have emerged due to the increasing usage ofelectronic devices and communication facilities in industry, commerce and military affairs. Agood way to solve this problem is to use microwave absorption materials to attenuate thoseunwanted electromagnetic energies. The ideal EM absorbers are required to have wideabsorption frequency range, strong absorption properties, low density, good thermal stability,and antioxidant capability. Graphene, a single atomic layer of sp2-hybridized carbon, forms atwo-dimensional honeycomb crystal lattice. Graphene possesses not only a stable structurebut also high specific surface area and excellent electronic conductivity. These propertiesmake graphene very promising as a kind of ideal EM absorber, however, the high carriermobility in graphene is harmful to its EM absorption in terms of impedance match mechanism.One of the most effective ways to solve the problem is to couple graphene with other types ofabsorbers. However, most research articles are focusing mostly on the two-dimensionalgraphene-based nanocomposites, and only a few studies are looking at graphene-basedhierarchical structures. In this paper, three-dimensional graphene-based materials have beenfabricated by combination with other types of absorber, and their microwave absorption hasbeen investigated. The main research results of this paper are as follows:A novel three-dimensional nanostructruer of graphene@Fe3O4@SiO2@NiO nanosheet arrayswere prepared by combining the versatile sol-gel process with a hydrothermal reaction.Graphene@Fe3O4composites were first synthesized by the reduction reaction between FeCl3and diethylene glycol (DEG) in the presence of GO. Then, graphene@Fe3O4was coated withSiO2to obtain graphene@Fe3O4@SiO2. Finally, NiO nanosheets were grown perpendicularlyon the surface of graphene@Fe3O4@SiO2and graphene@Fe3O4@SiO2@NiO nanosheetarrays three-dimensional structures were formed. Moreover, the microwave absorptionproperties of graphene@Fe3O4, graphene@Fe3O4@SiO2, graphene@Fe3O4@SiO2@NiOnanosheets arrays were investigated between2~18GHz microwave frequency bands. Theelectromagnetic data demonstrates that graphene@Fe3O4@SiO2@NiO nanosheetshierarchical structures exhibit significantly enhanced microwave absorption propertiescompared with graphene@Fe3O4and graphene@Fe3O4@SiO2, which probably originate fromthe unique three-dimensional structure combining large surface area and high porosity. Themaximum reflection loss value of graphene@Fe3O4@SiO2@NiO nanosheets arrays can reach-51.5dB at14.6GHz with a thickness of only1.8mm and the bandwidth corresponding to the reflection loss below-10dB is5.1GHz (from12.4to17.5GHz).A successful fabrication of novel three-dimensional graphene@Fe3O4noncluster@C@MnO2nanosheet arrays composites has been developed for the first time. The fabrication processinvolves deposition of Fe3O4nanocluster on graphene’s surface using a simple in situhydrothermal method, subsequent introduction of carbon on the surface of graphene@Fe3O4noncluster by combining the hydrothermal reaction and thermal treatment process, and finalformation of the hierarchical composites via a simple in situ redox replacement reactionbetween potassium permanganate (KMnO4) and carbon on surface of graphene@Fe3O4noncluster. Moreover, the microwave absorption properties of both graphene@Fe3O4nanocluster and graphene@Fe3O4nanocluster@C@MnO2nanosheet arrays hierarchicalcomposites were investigated between2~18GHz microwave frequency bands. Theelectromagnetic data demonstrates that graphene@Fe3O4nanocluster@C@MnO2nanosheetarrays hierarchical composites exhibit significantly enhanced microwave absorptionproperties compared with graphene@Fe3O4nanocluster, which probably originate from theunique hierarchical structure and larger surface area. The maximum reflection loss value canreach-38.8dB at15GHz with a thickness of only1.8mm and the bandwidth correspondingto the reflection loss below-10dB is5.4GHz (from12.3to17.7GHz).Two kinds of three-dimensional nanostructruer of graphene@Fe3O4@C@PANI (polyaniline)nanorod arrays were prepared by covalently and noncovalently grafting PANI nanorod arraysto the surface of graphene@Fe3O4@C, respectively. The measured electromagneticparameters show that the bonding form between PANI nanorod arrays andgraphene@Fe3O4@C have significantly effect on microwave absorption properties ofgraphene@Fe3O4@C@PANI nanorod arrays hierarchical structures, and the formation ofcovalent bond between PANI nanorod arrays and graphene@Fe3O4@C in hierarchicalstructures exhibits significantly enhanced microwave absorption performance. The maximumreflection loss is up to-44.2dB at11.4GHz and the absorption bandwidth with a reflectionloss below-10dB ranges from9.7to15.5GHz with a thickness of3mm. Therefore, the highmicrowave absorption performance with lightweight and wide absorption frequency band canbe realized by fabricating graphene-based hierarchical structures using covalent bondinteraction.A novel three-dimensional nanostructruer of N-doped graphene (NG)@PANI nanorod arrays modified with Fe3O4nanocluster have been fabricated by a hydrothermal reaction. Theas-prepared (NG@PANI@Fe3O4nanocluster) composites were characterized by XRD,Raman and FTIR spectra, VSM, XPS spectroscopy, TEM and FESEM. The results reveal thatthe surfaces of NG@PANI nanorod arrays are randomly covered by Fe3O4nanocluster withan average size of about40nm. With Fe3O4nanoclusters coated on the surfaces ofNG@PANI nanorod arrays, the composites exhibit superparamagnetic characteristics at roomtemperature. Moreover, the microwave absorption properties of both NG@PANI nanorodarrays and NG@PANI@Fe3O4nanocluster were investigated between2~18GHz microwavefrequency bands. The electromagnetic data demonstrates that NG@PANI@Fe3O4nanoclustercomposites exhibit significantly enhanced microwave absorption properties compared withgraphene@Fe3O4, which probably originates from improved level of impedance matching andinterfacial polarization. The maximum reflection loss of NG@PANI@Fe3O4nanocluster is-40.8dB at14.8GHz and the absorption bandwidth with a reflection loss below-10dBranges from10.4to15.5GHz with a thickness of2.7mm.A novel three-dimensional graphene@carbon nanotubes (CNTs) composite has been preparedby a facile one-pot pyrolysis strategy using urea as carbon source, and the density and lengthof CNTs on graphene are rationally tuned by adding an amount of urea to a precursor mixture.Correspondingly, the density and length of CNTs on graphene have significantly effect on themicrowave absorption properties of graphene@CNTs. When most of the graphene surface isclearly covered by the CNTs whose length ranges from300to600nm, the graphene@CNTscomposite exhibits excellent microwave absorption property. The maximum reflection lossvalue can reach-44.6dB at8.6GHz and the absorption bandwidth with a reflection lossbelow-10dB ranges from7.1to10.4GHz with an addition amount of only5wt%graphene@CNTs composite in the paraffin matrix.Three kinds of graphene@SiO2@NiO hierarchical three-dimensional structures,graphene@SiO2@NiO nanopartiles, graphene@SiO2@NiO nanosheet arrays andgraphene@SiO2@NiO nanoflowers were successfully fabricated by multi-step routes. Themeasured electromagnetic parameters show that graphene@SiO2@NiO nanosheet arrayscomposites exhibit enhanced microwave absorption performance with wide absorptionbandwidth as compared to graphene@SiO2@NiO nanoparticles and graphene@SiO2@NiOnanoflowers. The maximum reflection loss can reach-43.8dB at11.6GHz with a thicknessof3mm, and the absorption bandwidth with the reflection loss below-10dB is5.8GHz (from9.2to15GHz). In addition, the mechanisms for the enhanced absorption performanceare also discussed.