Preparation Of Electromagnetic Protection Materials Based On Graphe And MXene

With the development of 5G technology,electromagnetic radiation has become an"invisible killer",which has penetrated into all aspects of human life,causing certain interference to the normal use of electronic products and further endangering human health.Traditional electromagnetic protective materials can not tackle the current diversified and complex electromagnetic environment,therefore it is particularly urgent to study new electromagnetic protective materials,such as two-dimensional nano materials.Especially after the discovery of graphene two-dimensional materials,two-dimensional nano materials show excellent properties and broad application prospects in the field of electromagnetic protective materials because of their unique microstructure and physical and chemical properties.In recent years,MXene,as a new graphene-like two-dimensional material,has also become a research focus in the field of electromagnetic protective materials.However,the two-dimensional materials graphene and MXene have some problems in the preparation of electromagnetic protection composites,such as uneven dispersion,easy agglomeration and impedance mismatch,which is an enormous challenge for the structure design,component regulation and performance improvement of the composites.In this paper,we given a brief introduction about the classification and development of electromagnetic protection materials,and then we summarized the theoretical background and design criteria of microwave absorbing materials and electromagnetic shielding materials.After that,the research process,including the synthesis,structure and properties of graphene and MXene,as well as their applications in the field of electromagnetic protection materials has been reviewed.On the basis of previous work,this paper puted forward some approaches and methods for the current challenges in the research of electromagnetic protection materials.The main research work of this paper is as follows:(1)Given the poor impedance matching caused by the high conductivity of graphene,we reported a highly efficient,lightweight and broadband EMW absorber composed of 3D porous N-doped Ni@SiO₂/graphene network,which could be facilely constructed via pore structure modulation and architecture complexing/doping.The 3D porous graphene network was initially synthesized by Na Cl-template assisted high-temperature calcination.Then,low dielectric SiO₂layers were introduced through a modified St(?)ber method and formed a uniformly-dispersed Ni@SiO₂core-shell structure on the surface of graphene.Further calcinating of the composite under NH₃ atmosphere led to an N-doped graphene matrix.Owing to the well-defined interconnected porous architecture and synergistic effect from multiple absorption centers and diverse interfaces,the porous hierarchical N-doped Ni@SiO₂/graphene network exhibits superior EMW absorption in terms of both the minimum reflection loss(RL)value and the absorption bandwidth,as compared with graphene-based composites and most carbonaceous materials reported to date.The minimum RL value reaches up to-71.13 d B at 13.76 GHz with a thickness of 2.46 mm and the bandwidth corresponding to RL values less than-10 d B is 7.04 GHz(from 10.96 to18 GHz)with a low filler content of 15 wt.%.(2)In view of the impedance mismatch caused by the high conductivity of MXene,the plate-like MXene/SiO₂ composites with a unique core-rim microstructure(MXene@SiO₂)are rationally constructed by a simple St(?)ber method.The abundant functional groups on the edge of MXene leads to the formation of thick rim on MXene@SiO₂ nanoplates,which remarkably increases the interfacial polarization loss.Meanwhile,the SiO₂ coating with tunable thickness can balance the impedance at surface,which largely prevents the reflection of incident microwaves.As a result,very low specificreflection loss of-55.68 d B mm^-1 in Ku band is achieved in the composite with optimized coating thickness(0.95 mm).Moreover,the reflection loss lower than-20 d B(MA efficiency more than 99%)can always be achieved with certain matching thickness lower than 2mm in the whole X and Ku band.These findings imply that the 2D core-rim MXene@SiO₂nanoplates can be applied as ultrathin microwave absorber in various portable device.(3)On the basis of the synthesized monodisperse absorbing functional structural unit MXene@SiO₂,we synthesized PEDOT:PSS/MXene@SiO₂ foam composite with ordered layered porous structure via ice template method.MXene@SiO₂ was dispersed uniformly on on the surface of PEDOT:PSS.By systematically analyzing the evolution of the microstructure during the synthesis process,we found that with the increase of content of MXene@SiO₂,the structure gradually evolved into multi-scale structure.The results showed that when the mass fraction of MXene@SiO₂ in the composite is 53.57 wt.%,excellent microwave absorption performance could be achieved,and the minimum reflection loss is<-30 d B(>99.9%electromagnetic wave is absorbed)with the tunable thickness from 2 mm to 3.2 mm.The minimum RL value reached up to-58.58 d B at 10.95 GHz with a thickness of 2.77 mm,and the effective absorption bandwidth was3.57 GHz,covering 85%of the whole X-band.(4)Based on the study of MXene composite powder,the research of bulk MXene composite was carried out.Taking MXene as the second phase,we prepared MXene/PANI bulk material by spark plasma sintering(SPS)and studied its electromagnetic shielding performance.With the increase of MXene content,the composite gradually evolved into a layer by layer stacking structure,which is conducive to enhance the multiple internal reflection loss of electromagnetic wave in the material.The introduction of MXene can improve the conductivity of the material,leading to the enhanced conductive loss of the material.In addition,the rich functional groups on the surface of MXene can also enhance the dipole polarization loss of the material.The results show that the composite with the 40 wt.%addition of MXene can achieve the best shielding efficiency,reaching?24 d B in the range of 8.2-12.4 GHz,meeting the needs of commercial applications.