Research On Microstructure Regulation And Electromagnetic Shielding Performance Of MOFs-derived Carbon-based Composite

With the continuous development and application of communication technology,smart products,and electronic technology,electromagnetic waves（EMW）have brought great convenience to people’s lives,while the problem of electromagnetic radiation also becomes increasingly prominent.Electromagnetic interference（EMI）shielding and absorbing materials are mainly used to attenuate or absorb EMW and reduce the pollution or damage caused by EMW to the human body or the environment.Metal-organic frameworks（MOFs）are considered as one of the ideal precursors for efficient EMW absorbing materials and green EMI shielding materials due to their tunable structures,uniform porosity distribution and large specific surface area.In addition,MOFs can be transformed into porous carbon decorated with metal species at appropriate pyrolysis temperatures.And carbon-based composites have the advantages of lightweight,high dielectric loss and easy doping and recombination with other materials.By adjusting its microstructure,the dielectric loss materials and magnetic loss materials can be effectively combined to realize the optimization of electromagnetic parameters,material density and shielding and absorbing properties,so as to meet the requirements of a new generation of shielding and absorbing materials for lightweight,broadband,and high absorption.In this manuscript,the design and regulation of the microstructure of MOFs derived carbon matrix composites were studied.The organic combination of solvent self-assembly,in-situ growth,hydrothermal synthesis,etching/ion-exchange reaction,and low-temperature phosphating were used to prepare carbon matrix composites with different microstructures.The effects of different microstructures on the electromagnetic shielding and absorbing performance and the mechanism analysis were studied.The main contents of the paper are as follows:（1）To solve the problem of narrow absorption bandwidth of traditional absorbing materials,this manuscript adopts the idea of combining high-porosity rhombic dodecahedral MOFs with multiphase 1T-2H-Mo S₂ to prepare flower-like core-shell structures.The effect of different thermal temperatures on the microstructure morphology under a protective atmosphere was studied.The relationship between electromagnetic parameters,EMW reflection loss（RL）,and microstructure in the 2-18 GHz frequency band is investigated.The results show that the adjustment of the heat treatment temperature can effectively adjust the electromagnetic parameters.The Zn Co@C@1T-2H-Mo S₂-7 sample heat-treated at700℃,which has an excellent minimum reflection loss(RL_min)value of-35.83 d B when the thickness is 5.0 mm,effective absorption bandwidth（RL<-10 d B）up to 4.56GHz at 2.0 mm thickness.The excellent EMW absorption performance is attributed to the flower-like core-shell structure and the dielectric/magnetic synergistic loss mechanism of Zn Co@C@1T-2H-Mo S₂ particles.The EMW loss mechanism of the material was further analyzed.The material’s intrinsic dielectric polarization relaxation loss mechanism is dominant,supplemented by magnetic loss mechanisms such as natural resonance and eddy current loss.（2）In order to solve the problems of difficult processing and poor stability of MOFs-derived carbon-based absorbing materials in practical applications,cotton fabric（CF）is used as the substrate,and Co-MOF nanosheets containing cobalt are grown in situ on the surface of CF,and CoFe-LDHs nanosheets is formed by etching/ion-exchange reaction.CoFe/C/HCF composites with hierarchical pore structures were obtained by high-temperature pyrolysis in an inert protective atmosphere.The hierarchical pore structure was verified using a small-angle neutron scattering analysis.The results show that the composite has higher average shielding efficiency（SE）and specific shielding efficiency（SSE）,reaching 30.7 d B and 109.64d Bcm³g^-1,respectively,at a thickness of 0.90 mm.Due to the introduction of CoFe metal particles,the magnetic loss mechanism of the composite is increased,and the impedance matching is optimized,which makes the composite exhibit excellent EMI shielding performance.The unique hierarchical pore structure,strong interfacial interaction,and dielectric/magnetic heterogeneous composition further promote a variety of polarization loss mechanisms.（3）In order to reduce the thickness of composites and improve the bonding mode of MOFs structural units and flexible substrates,two-dimensional graphene oxide（GO）rich in oxygen-containing functional groups were introduced as the research focus to prepare MOFs-derived carbon-based composites of carbon materials of different dimensions.GO was decorated on the surface of CF through layers of self-assembly.The oxygen-containing functional groups on the surface of GO provided growth sites for Co-MOF which reacted with Mo O₄^2-in sodium molybdate aqueous solution to form Co Mo O₄ nanosheets in situ.The effect of different GO contents on the EMI shielding performance was studied,and the frequency domain simulation was performed using COMSOL Multiphysics to analyze and visualize the shielding mechanism of the interaction between Co Mo Px/RGO/C composites and EMW.The composite has a higher average SE,SSE,and SSE/t at a low density of 0.19 g/cm³,reaching 31.5 d B,165.79 d Bcm³g^-1and 6140.35 d Bcm²g^-1,respectively,and its thickness is 0.27 mm.The excellent shielding performance of thin and light composite materials is attributed to the unique honeycomb structure that can extend the propagation path of incident waves,promote multiple reflections of EMW,and synergistic effects between material assemblies of different dimensions,to further improve the dissipation capacity of EMW.In this paper,MOFs-derived carbon-based composites with different compositions,structures,and morphologies were prepared by using MOFs as functional materials to gradually optimize the EMI shielding and absorption properties of carbon-based composites through microstructure control.Under the synergistic effect of various loss mechanisms such as dielectric loss and magnetic loss,the EMI shielding and absorbing properties of composite materials can be effectively regulated to obtain new EMI shielding and absorbing materials.