| The research of absorbing materials never slack,which put down to the issues of safety pollution that the wide application of electromagnetic wave in the fields of national defense and civil electromagnetic protection.With the rapid development of wireless technology,the research trend of absorbing materials is gradually changing to low-dimensional materials,composite,frequency band,broadband and diversified functions.Polyoxometalates(POMs),as a compound of transition metal wrapped by a large amount of oxygen atom,have attracted wide attention due to the combination of exquisite structures,abundant elements and powerful functions.Keggin-type POMs not only have a band gap structure that was similar with semiconductor,but also have variety,high activity selectivity and independent coordination capacity.However,this unique cage geometry has a large number of voids,which is not conducive to carrier migration and have poor conductivity.Therefore,this paper focuses on the composite absorbing materials with multiple electromagnetic loss mechanisms and special structures,which are obtained by matching and compounding POMs materials,conductive polymers and other materials through core-shell structure design or self-assembly and carbonization with organic ligands.In this paper,based on the material structure design,the inorganic material POMs are combined with organic conductive polymer material(PANI)through electrostatic self-assembly,were loaded to NiCo2O4 and Fe2O3,and achieved a good absorbing effect.Or the POMs/dopamine supramolecular electrostatic self-assembly structure was combined with magnetic material(Co Fe2O4),to obtain the transition metal carbide,magnetic alloy and nitrogen-doped carbon skeleton structure through carbonization strategy.The enhance of electromagnetic wave absorption capacity contribute to achieve the goal of thin,light,wide and strong.(1)By hydrothermal combined electrostatic self-assembly method,transition oxometalates as anionic phase,aniline as organic ligand and NiCo2O4 as supporting matrix,the porous framework nanocomposite absorbing material(NiCo2O4@acid doped PANI/?-Si W11Mn)was prepared.Acid doped polyaniline as conductance loss phase anchored on the surface of NiCo2O4with a high aspect ratio,made the whole material had a certain electrical conductivity,which can achieve the purpose of improving electromagnetic parameters and regulating electron transport properties.Other groups served as dielectric loss to balance the impedance matching.In addition,designing the frame structure could effectively reduce the density and the equivalent dielectric constant.NiCo2O4@acid doped PANI/?-Si W11Mn nanocomposites showed excellent absorption properties.When the amount of absorbent was 35 wt%,the maximum RL could reach-52.4 d B at only 1.9 mm,and the effective absorption band width(RL?-10 d B)could reach 6.5 GHz.The maximum absorption was-60.4 d B(2.4 mm),the effective absorption bandwidth was 6.5 GHz(2.9 mm)in the range of 1.5-5 mm,and the bandwidths below-10 and-20 d B were 13.9 and 11.1GHz,respectively.(2)Combined with carbonization strategy,Mo2C/Fe Co/NC was designed by electrostatic self-assembly using molybdate,organic ligand dopamine and magnetic cobalt ferrite.By adjusting p H value and the types of surfactants,three kinds of nanostructures,such as flower spherical,lily cluster and butterfly state,were obtained.The results showed that the best sample(8.5-Mo2C/Fe Co/NC)exhibited superior electromagnetic wave absorption performance with an effective absorption bandwidth(RL?-10 d B)of 10.27 GHz(3.4 mm)and effective absorption area of 135.57(d B·GHz).Moreover,the RL of anionic Mo2C/Fe Co/NC reached-60.18 d B(2.8 mm).The maximum RL of cationic Mo2C/Fe Co/NC reached-77.37 d B(2.2 mm).In addition,an effective bandwidth of 7.25 GHz can be obtained at a thickness of 2.2 mm.(3)Nickel(II)substituted?-Keggin polyoxometalates and polyaniline coated Fe2O3 hollow nano spindles(Fe2O3@PANI/?-Si W11Ni)were successfully prepared by hydrothermal method and electrostatic self-assembly.Fe3+was first hydrolyzed and polymerized into Fe2O3,and then dissolved into[Fe(H2PO4)x]3-X,resulting in a hollow structure.On the polyaniline chain,the polyoxometalates existed in the form of proton doped counter-ions and bineded to the N atoms of amine and imine on the chain((-NH+=)/?-Si W11Ni).The results showed that the maximum RLvalue reached-53.6 d B at 3.5 mm and 6.9 GHz,and the maximum absorption bandwidth(RL?-10 d B)was 6.3 GHz when the thickness was only 1.9 mm. |
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