Preparation And Electromagnetic Wave Absorbing Performance Of MXene-based Nanocomposites

Electromagnetic wave protection materials have been widely used in national defense,medical care and many other fields.As a new type of two-dimensional absorbing material,two-dimensional layered metal carbide(MXene)has a unique layered structure,good conductivity,numerous surface functional groups and defects,and has broad application in energy storage materials,adsorption materials,electromagnetic wave absorption.In the aspect of absorbing materials,its unique structure and characteristics make it widely used,but its high conductivity will bring about poor impedance matching,which restricts the absorption performance of electromagnetic waves.In this paper,MXene(Ti3C2Tx)was taken as the research target,and MXene-based nanocomposites were prepared by doping,calcination,magnetization and compounding.The composition,morphology and structure of the composites were studied and analyzed,and the electromagnetic wave absorption performance of nanocomposites was studied by vector network analyzer,and the related absorbing mechanism was discussed.The research results are as below:(1)By doping Fe3O4,PPy@β2-Si W11 Co on the surface of MXene,an efficient nano-composite absorber was successfully prepared.Polyoxometalate and hydrochloric acid were used as protonic acid doped polypyrrole,and anions were attached to the main chain,so that the electromagnetic parameters could be adjusted and the nano-composite material could easily achieve the best conductivity and impedance matching.Fe3O4 introduced magnetic loss,and the free movement of Fe2+ and Fe3+ caused multipolarization.Defects,dipoles and dangling bonds in nanocomposites induced dipole polarization;Charge accumulates at the three-phase interface,resulting in interfacial polarization.The effects of different products,different loading rates and different component ratios on the microwave absorbing properties of nanocomposites were studied.When the loading rate was 45 wt%,the best reflection loss of MXene/PPy@β2-Si W11Co/Fe3O4 nanocomposites could reach-62.6 d B at 1.7 mm,and the effective absorption bandwidth of 9 GHz could be obtained in range of 1.5 ~ 2.9 mm.(2)S-MXene(Ti O2)produced by calcination of MXene and thiourea at high temperature provides abundant defects and functional groups,and the resulting dipole polarization relaxation optimizes the dielectric properties.The introduction of Ag improved the conductivity of nanocomposites,while Co Ni alloy could improve the magnetic loss and impedance matching.Appropriate synergy of conductivity,dipole polarization,interfacial polarization and magnetic loss could enhance the electromagnetic wave absorption of nanocomposites.The reflection loss of S-MXene(Ti O2)/Ag/Co Ni nanocomposites was-63.1d B when the thickness at 2.1 mm(the loading rate was 50 wt%),and the effective absorption bandwidth was 5.2 GHz at 2.0 mm.Moreover,by adjusting the composition proportion and loading rate of nanocomposites(S-MXene(Ti O2): Ag: Co Ni =6: 6: 6;the loading rate was 55wt%),the minimum reflection loss at 1.5 mm was-80.9 d B.(3)MXene/NPC@W(O)x/Ni nanocomposites were successfully synthesized by means of self-assembly and carbonization.Polypyrrole doped with phosphotungstic acid was carbonized to form NPC@W(O)x material.The defects formed after carbonization indicated more dipole polarization,and the polycrystalline multiphase formed after carbonization caused multiple interfacial polarization,which optimized the dielectric properties of the nanomaterial.The introduction of Ni would adjust the electromagnetic parameters,increased the loss mechanism and optimized the impedance matching.The MXene/NPC@W(O)x(Fe Cl3)/Ni nanocomposites showed good absorption performance of incident electromagnetic waves at a very thin thickness.When the load ratio was 45 wt% and the thickness was 2.0 mm,the MXene/NPC@W(O)x(Fe Cl3)/Ni nanocomposites had the minimum reflection loss of-63.8 d B,and the corresponding effective frequency bandwidth was 5.5 GHz.If the thickness range was adjusted to 1.7 ~ 3.5 mm,the effective frequency bandwidth could reach 9 GHz.