| Carbon-based electromagnetic shielding and absorbing materials have become one of the ideal electromagnetic functional materials for solving radar and electromagnetic interference problems in military and civilian fields due to their light weight,controllable composition and structure,and good electric performance.However,the single carbon materials usually hardly satisfy the comprehensive performance of“thin-thickness,lightweight,broadband,strong absorption”for electromagnetic wave absorption and shielding because of its intrinsic poor impedance matching characteristic derived from its nonmagnetic properties.Therefore,the combination of the lightweight conductive carbon materials and the magnetic materials can help to improve the impedance matching characteristics and maintain high electromagnetic wave loss,realizing the lightweight,broadband absorption and strong absorption characteristics.This paper focuses on fabricating carbon-based magnetic composites with ferrite and alloys as magnetic component,and prepare the biomass-derived carbon-based magnetic Fe3O4/CF composites,MOF-derived hollow carbon-based magnetic composites(Co Ni@C,CNC)and porous Co Fe2O4/RGO(CFO/RGO)nanocomposites with lightweight,broadband,strong absorption by controlling the component,structure and morphology of the composites.Meanwhile,an ultra-thin and ultra-lightweight graphene-based hybrid film(CFO-CNTs/RGOp)was prepared by designing graphene interlayer structure to obtain a high-strength,hydrophobic and ultraviolet-resistant EMI shielding materials.The main research contents and results of this paper are listed as follows:1.Biomass-derived carbon-based magnetic Fe3O4/CF composites with porous structure were prepared by using solution immersion method and high temperature calcination method.Scanning electron microscopy(SEM)results showed that magnetic Fe3O4 particles were uniformly embedded and dispersed on the surface of carbonized CF.The nitrogen absorption and desorption curves and room temperature hysteresis loop results performed that increasing the content of Fe3O4 can decrease the specific surface area and increase the Ms values of Fe3O4/CF composites.The Raman spectra results of Fe3O4/CF composites with different calcination temperatures exhibited that increasing the calcination temperature could cause more defects.The electromagnetic parameters and the microwave absorption properties of Fe3O4/CF composites were tested by the coaxial method.The results showed that the content of Fe3O4 and calcination temperature have the great influence on the microwave absorption performance of Fe3O4/CF composites.With the mass ratio of precursors of CF and Fe3O4 was 1:1 and the calcination temperature was 700~oC,the as-prepared Fe3O4/CF-1-700 sample obtained the superior absorbing performance.The minimum reflection loss was about-48.2 d B,and the effective absorption frequency range could reach 5.1 GHz(12.9-18.0 GHz)with the thickness of only 1.9mm.2.The bimetallic Co Ni-MOF precursor was prepared by solvothermal method,and Co Ni@C(CNC)composites with hollow structure and porous structure were obtained by calcination at high temperature under the inert gas atmosphere.SEM and TEM results showed that the spherical CNC composites exhibited the typical hollow structure and porous structure.By simply adjusting the mass ratio of Co/Ni,the size,microstructure,specific surface area,pore structure,magnetic properties and electromagnetic parameters of the CNC composites were precisely controlled.When the filling amount of the CNC-1:1 composite was 30 wt%and the thickness of the sample was 2.4 mm,the minimum reflection loss reached-37.5 d B at 10.7 GHz,which indicated the electromagnetic wave absorption efficiency was over 99.9%.Meanwhile,the effective absorption bandwidth could reach up to 4.0 GHz(8.0GHz-12.4 GHz).3.Porous CFO/RGO nanocomposites were prepared by in-situ solvothermal method.The results of SEM and TEM analysis showed that loose and porous CFO nanospheres with a diameter of about 180 nm were evenly distributed on the RGO surface,which constituted hierarchical structure of CFO/RGO nanocomposites.Electromagnetic parameters showed that with the increase of the CFO content,the dielectric constant of the CFO/RGO composite material was significantly decreased and the microwave absorption performance was improved.The effect of the content of the CFO/RGO nanocomposites on the microwave absorption properties was studied by changing the amount of CFO/RGO 10:1 nanocomposites in the wax matrix.When the CFO/RGO 10:1 was 50 wt%and the sample thickness was 2.8 mm,the minimum RL value was about-57.7 d B at 10.2 GHz,and the effective absorption frequency rangeed from 8.3 GHz to 14.1 GHz(5.8 GHz).4.The ultra-lightweight and ultra-thin CFO-CNTs/RGOp hybrid film was prepared by solution spraying method and high-temperature reduction method with the reduced graphene oxide as the matrix material,the CFO-CNTs nanocomposites as the electromagnetic functional materials,and the cross-linking small molecule as the reinforcing system.SEM results showed that the prepared CFO-CNTs/RGOp hybrid film exhibited a typical parallel layer structure.The introduction of CFO-CNTs composites contributed to form the enhanced conductive network and magnetic loss,improving the attenuation of electromagnetic waves.At the same time,the abundant interfaces between CFO-CNTs and RGO could cause more interfacial polarization and dielectric loss,further improving the absorption loss of the hybrid film.The results of electromagnetic shielding analysis showed that when the thickness of CFO-CNTs/RGOp hybrid film was 15μm,the shielding effectiveness in X-band reached about 38.0 d B,showing that the shielding efficiency exceeded 99.9%.The test results of water contact angle and tensile strength indicated that the CFO-CNTs/RGOp hybrid film performed excellent hydrophobicity and superior mechanical strength.The UV aging test results exhibited that the tensile strength and electromagnetic shielding effectiveness of the hybrid film after UV aging could still reach 82.4%and 86.6%of that before the aging test,indicating that the CFO-CNTs/RGOp hybrid film showed excellent UV aging resistance. |
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