Construction And Microwave Absorption Performance Investigation Of Conductive-Dielectric Absorbing Composites

As an important carrier of information transmission in modern society,electromagnetic（EM）waves were widely used in many fields.But widely use of the EM wave also had brought more and more serious electromagnetic wave pollution at the same time.Herein,the research on high-performance composite absorbing materials with"light-weight,wide absorbing frequency bandwidth,strong absorption and high temperature resistance"had attracted much attention.Graphite Nanoplatelets（GNPs）were light weight,cheap in price,resistant to high temperature and good in conductivity.This paper reviewed microwave absorbing materials at domestic and abroad,especially conductive loss materials,and found that GNPs was a kind of promising absorbing material,which can effectively attenuate the incident electromagnetic wave.Through microwave absorbing performance research,it was found that the main factor which limiting the absorbing performance of GNPs were its high conductivity leading to poor impedance matching performance.Considering above-mentioned facts,a series of conductive-dielectric absorbing composites were prepared.The results shown that as-proposed supercapacitor-like model structure can significantly enhanced the microwave absorption.And we proposed a new method used to prepare high-performance conductive-dielectric composite absorbing materials by modified the surface of conductive loss materials（GNPs and MXenes）via introducing dielectric loss materials.The detail investigations were as follows:1.GNPs were modified with metallic Ni magnetic particles by electroless nickel plating,hoping to increase the magnetic loss and enhance the microwave absorption performance of GNPs.However,studies had found that the absorbing property of GNPs/Ni composites were weaker than pure GNPs.The comparative analysis of the impedance matching contour map and the reflection loss contour map found that the main factor which limiting the microwave absorption performance（MAP）of GNPs was its poor impedance matching,which was attributed to the high conductivity.In order to optimize the impedance matching performance of the material,a series of GNPs/Ni_xS_y/Mo S₂ composites were prepared by using hydrothermal method via adjusting the molar ratio of molybdenum and sulfur,and the microwave absorption mechanism of all the samples were systemically investigated at 2.0 GHz～18 GHz.The results showed that the supercapacitor-like model structure constructed through vertically loading the dielectric material（Ni_xS_y/Mo S₂）on the surface of the GNPs conductive material effectively optimized the impedance matching of the conductive material,and the conduction loss polarization loss synergistic effect greatly enhanced the absorbing performance of the composite material.When the molar ratio of molybdenum to sulfur was 1:6,the GNPs/Ni_xS_y/Mo S₂composite material had the best absorbing property,the minimum reflection loss reached-43.3 d B at the sample thickness of 2.2 mm.and the efficient microwave absorbing bandwidth achieved up to3.6 GHz.2.Covalently grafted PANI nanorod-arrays on the surface of GNPs via diazo reaction and in-situ polymerization,and controlled the conductivity and microscopic morphology of the material by adjusting the doping concentration of proton acid,a series of supercapacitor-like model structures of GNPs-PANI nanorod-array composite material were prepared.Conductivity analysis showed that the PANI nanorod-array significantly reduced the conductivity of GNPs（more than 2 orders of magnitude）.Additionally,with increasing doping concentration of the proton acid,the conductivity of GNPs-PANI composites raised.Study on the microwave absorption performance exhibited that when the proton acid doping concentration was 1 mol/L,the GNPs-PANI nanorod-array composite material had excellent microwave absorption performance（MAP）,and the effective absorption width reached up to 5.8 GHz（6.0GHz～11.8 GHz）,the minimum RL value was-38.56 d B at 7.0 GHz.The comparative analysis of impedance matching contour maps showed that the impedance matching of the material was significantly optimized through covalently grafting the PANI nanorod-array on the surface of GNPs.With the synergistical contribution of conductivity loss of GNPs and dipole polarization loss of PANI nanorod,the microwave absorption performance of GNPs-PANI composites got enhanced.And the general applicability of the supercapacitor-like model in GNPs-based composite absorbing materials had been verified.3.Two kinds of supercapacitor-like GNPs/Zn O nanocomposites（GNPs/Zn O nanorod arrays and GNPs/Zn O nanoneedles）were synthesized,and the microwave absorption performance together with the relevant mechanism were investigated based on the different microstructures,followed by the discussion of the growth mechanism of Zn O nanorod and nanoneedle.According to the detail analysis,we found that the pathways of attenuation EM wave were the same,and the differences between each other were responsible for the different intensity of interface polarization,due to the different microstructures.Study on microwave absorption showed that when the thickness of the sample was at 2.4 mm,the minimum reflection loss of GNPs/Zn O nanorod-array composites at 10.5 GHz was-44.8 d B,and the effective absorption bandwidth was 4.65 GHz（7.0 GHz～11.65 GHz）.When the sample thickness was at4.0 mm,the effective absorption bandwidth of the GNPs/Zn O nanoneedle-like composite covered the whole X-band,reaching up to 6.7 GHz and the RL was only-15.3 d B.The thermal stability analysis（TGA）analysis results showed that the GNPs/Zn O nanorod-array composite material could be stably used under air atmosphere less than 600°C,which had potential application value in the field of high-temperature microwave absorption.4.Novel two-dimensional material MXene（Ti₃C₂T_x）with higher conductivity was prepared via HF etching and post treated by alkaline solution.As-prepared Ti₃C₂T_xconductivity was 339 S/cm.Study on microwave absorption showed that the main limiting factor of Ti₃C₂T_x’s MAP was impedance mismatching.Thus,a series of MXene/Ti O₂/Mo S₂with supercapacitor-like model structure was prepared by one step hydrothermal reaction.It was found that the conductivity of as-prepared MXene/Ti O₂/Mo S₂ composites were significantly reduced after introducing dielectric loss materials,and the conductivity decreased with the time expanding.Moreover,when the reaction time reached 5 h,the optimum RL value of MXene/Ti O₂/Mo S₂ were-60 d B and the corresponding effective bandwidth reached up to 4.6 GHz（12.2GHz～14.2 GHz）with the coating thickness of 3.4 mm.The enhanced MAP originated from better impedance matching and the synergistic effect of conductive loss and dipole polarization of MXene and Ti O₂/Mo S₂.And the general applicability of the supercapacitor-like model in MXene-based composite absorbing materials had been verified.