Design,Fabrication And Research On Electromagnetic Protection Properties Of Ti₃C₂T_x MXene-Based Composites

With the rapid development of wireless communication equipment and radar detection technology in the high frequency range,electromagnetic wave absorbing and shielding materials have attracted great attention as an effective response strategy in biological protection,stealth technology,communication security and information processing technology.As a new type of two-dimensional nanomaterial,Ti₃C₂T_x MXene has excellent response to electromagnetic waves due to its special atomic arrangement structure,tunable surface wettability,and ultra-high intrinsic conductivity.However,for pure MXene materials,the single decay mode and insufficient interfacial polarization limit their practical application in precision electronic devices.Therefore,it is necessary to modify MXene materials to improve the electromagnetic wave absorption property of MXene composites.This thesis firstly introduces magnetic nickel nanochains to modify and enrich the microstructure of MXene nanomaterials.Subsequently,we obtain excellent electromagnetic wave absorption and shielding properties through geometric amplification effect and dielectric-magnetic loss synergistic effect.Correspondingly,we proposed a diagram of the dielectric/magnet composition and conductivity vs.electromagnetic wave absorption and shielding performance;We prepared homogeneous magnetic nanoparticle-loaded MXene composites and optimized the electromagnetic parameters and impedance matching properties of MXene,and obtained excellent wave absorbing effects;On this basis,by introducing carbon nanotubes,the shielding effect and mechanical strength of the composite film are improved;The innovative design of magnetic MXene/graphene aerogel solves the problem of high filling and low efficiency of absorbing materials in polymers.The research contents and results are as follows:（1）In the second chapter,a promising electromagnetic wave absorbing and shielding material,MXene/Ni chain hybrid material,is designed and developed,which consists of 1D nickel nanochains and 2D MXene nanosheets.The excellent electromagnetic wave absorption and shielding properties of the composites can be obtained and controlled only by adjusting the MXene content in the hybrids.When the MXene content is 10 wt%,at 11.9 GHz,the minimum reflection loss(RL_min)can reach-49.9 d B only with a thickness of 1.75 mm.When the MXene content was further increased to 50 wt%,the best electromagnetic shielding effectiveness（SE）reached 66.4 d B.The analysis of the data results shows that the synergistic effect of conductive MXene and magnetic nickel nanochains contributes to the excellent electromagnetic wave absorption and shielding properties of the hybrid material.Under the appropriate ratio of dielectric and magnetic materials,the composite material obtains excellent wave absorbing effect,while at higher electrical conductivity,it is positively related to the electromagnetic shielding effectiveness.Finally,based on the experimental results,we propose phase diagram guidelines for the design of absorbing and shielding materials.（2）According to the proposed material design phase diagram criteria,in Chapter 3,we developed a facile,mild,and large-scale cosolvothermal method by tuning the electrical conductivity of MXene composites,namely in situ growth of uniform and size-controllable MXene surfaces of nickel nanoparticles.Subsequently,the hybrids were uniformly dispersed into the dielectric PVDF,in order to greatly enhance its electromagnetic wave absorption ability.The results show that the Ni@MXene hybrid exhibits stronger reflection loss(RL_min=-52.6 d B at 8.4 GHz),broad effective absorption bandwidth（EAB=3.7 GHz,including 71%of the X-band）,low loading（10 wt%Ni@MXene）,and thin thickness（3.0 mm）,meeting the requirements of“strong ansorbing ability,wide effective band,light weight,and thin thickness”absorbing materials.By adjusting the sample thickness,the effective bandwidth can completely cover the entire X-band,up to 6.1 GHz,so the Ni@MXene hybrid material has great potential as an aircraft stealth coating.（3）On this basis,in Chapter 4,magnetic MXene and conductive carbon nanotubes were assembled into flexible Ni Co/MXene-CNT films with layered microstructure by vacuum filtration,thereby simultaneously obtaining high conductivity properties and enhanced electromagnetic wave attenuation.The electromagnetic wave shielding ability of only 53μm Ni Co/MX-CNT composite film can achieve 90.7 d B,which means that the obtained film product can reflect and absorb 99.9999991%of electromagnetic waves.Under the same quality,the shielding effect of the composite film is even better than that of pure CNT film and pure MXene film with higher conductivity.Furthermore,by adjusting the film thickness from 9μm to 116μm,the modulation of EMI shielding performance from46 to 105 d B can be achieved.In addition,the densely layered structure endows the composite membrane with excellent flexibility,foldability,and robust mechanical properties.（4）Finally,in Chapter 5,to solve the problem of high filling and low efficiency of nanofillers in the matrix,we constructed magnetic nanochain-supported 3D dielectric Mxene/reduced graphene aerogels by directional freezing method and hydrazine vapor reduction method.Using this preparation method of nanofiller pre-assembly,the formed oriented unit structure and heterodielectric/magnetic interface optimize impedance matching,enhance multiple interface polarization and electric/magnetic coupling effect.Interestingly,the as-prepared ultralight Ni/MXene/RGO aerogel reported the best electromagnetic wave absorption performance among MXene-based composites to date,with a minimum reflection loss of-75.2 d B.Furthermore,the excellent structural robustness,high hydrophobicity and thermal insulation properties ensure stable and durable electromagnetic wave absorption applications of Ni MR-H aerogels against deformation,water or humid environments,and high temperature environments.In this thesis,a design relationship criterion between electrical conductivity and electromagnetic wave absorbing and shielding materials was proposed;a universal preparation method of magnetic nanoparticle-loaded MXene absorbing materials is developed;a flexible film with reliable mechanical strength and high shielding efficiency was designed;the ubiquitous problem of high filling and low efficiency of microwave absorbing nanofillers,which opens up a new direction for future research on electromagnetic wave absorption and shielding materials was solved.