Study On The Construction Of MOFs Derived Nanocomposites And Their Electromagnetic Absorption Properties

The rapid development of electronic technology and radio communication technology inevitably brings the problem of electromagnetic pollution,electromagnetic pollution not only affects the health of human beings,animals and plants,but also affects the normal work of science,medicine and other precision equipment,and even has brought a certain threat to national defense security.Therefore,it is urgent to develop electromagnetic protective materials to reduce electromagnetic pollution.Metal-organic frameworks(MOFs)are porous crystalline materials formed by the coordination of metals and organic matters.They have special physical and chemical properties and have been widely studied in many fields.In the field of electromagnetic wave absorption,MOFs derivatives,as a new kind of absorbing materials,have the advantages of easy synthesis method,good stability,high porosity,and large surface area.Moreover,the magnetic components in the derivative have the characteristics of uniform dispersion.However,there are many limitations for a single component as an absorbing material,for example,the thickness of the absorbing layer is thick,the amount of addition in the matrix is large,and the absorbing performance is not good enough to meet the needs of efficient absorbing materials.Therefore,it is of great significance to prepare composite materials based on MOFs and their derivatives.In this paper,ZIF series MOFs with zeolite-like structure,carbon materials and ceramic materials were used to prepare composite materials.Then,the changes of the structure and the composition of the composites were studied before and after calcination.Finally,the electromagnetic parameters of the composites are analyzed to discuss their absorbing properties and absorbing mechanism.The main research contents and results of this paper are as follows.(1)Construction of 2D Hybrid Composites Derived from MOFs and Their Electromagnetic Absorption CharacteristicsThe formation of interface in composites plays an important role in improving the absorption of electromagnetic waves.In this work,the preparation of composites is divided into two steps.Firstly,the in-situ growth method is used to control the growth of Co-MOFs on the surface of GO nanosheets.Secondly,MOFs/GO is calcined by controlling the temperature change process.The microstructure of the composites was analyzed by electron microscopy,and the structural characteristics and components of the composites were analyzed by FT-IR,Raman and XRD before and after calcination.Using vector network analyzer to obtain the electromagnetic parameters of the preparation of material and its detailed analysis,the results show that the derivative of the MOFs/GO in matrix is only 6 wt%,show the high efficiency for the electromagnetic wave absorption,the effective absorption of width up to 7.72 GHz,cover the whole X-band electromagnetic wave(8-12 GHz),compared with other electromagnetic wave absorbing materials,it showed a wide absorption width,low percentage in the matrix.The reason for the good absorbing performance is that the interface effect of MOF derivatives and RGO increases the electron transfer between the components in the material,which increases the loss of electromagnetic wave,and the good impedance match makes electromagnetic wave enter the material better.(2)Sandwich CoFe₂O₄/RGO/CoFe₂O₄ Nanostructures for High-Performance Electromagnetic AbsorptionReasonable design of nanostructured materials with conductive and magnetic properties is of great significance in the field of electromagnetic absorption.So far,it has been difficult to uniformly cover the surface of reduced graphene oxide(r GO)with magnetic components,especially through the pyrolysis strategy of MOFs,because the particle size of MOFs is generally large and it is difficult to uniformly distribute on the surface of r GO after growth.Here,by adding Fe³⁺in the synthesis process of Co-MOFs precursors,we successfully deposited MOFs on GO uniformly to form MOFs/GO/MOFs with sandwich morphology.Then,MOFs/GO/MOFs were transformed into sandwich CoFe₂O₄/RGO/CoFe₂O₄ by controlled temperature.It was clearly observed by SEM and HRTEM that magnetic component CoFe₂O₄in the MOFs derivatives was evenly distributed on the surface of RGO after heat treatment.The electromagnetic parameters of CoFe₂O₄/RGO/CoFe₂O₄ composite were obtained by using vector network analyzer.The results show that the composite nanomaterials exhibit remarkable electromagnetic absorption performance.The effective absorption width reaches 7.08GHz at2.6mm,showing the characteristics of thin thickness and wide width.It is believed that the effective combination and synergistic effect between the dielectric and magnetic components not only increases the impedance matching of the composites,but also effectively utilizes the dielectric and magnetic properties of the composites.In addition,the increased interface effect also plays an important role in the electromagnetic loss.(3)In Situ Stringing of Metal Organic Frameworks by SiC Nanowires for High-Performance Electromagnetic Radiation EliminationThe design of nanocomposites with novel structure is considered to be one of the effective ways to adjust the absorbing properties of materials.In this work,we used in situ growth strategy to construct the MOFs/SiC composite absorbing material,which has the similar structure like barbecue string.First,MOFs crystal particles were connected by one-dimensional SiC nanowires in series.Then,MOFs/SiC are treated at high temperature in air and argon respectively.Finally,a vector network analyzer was used to test and analyze the calcined composite materials,and it was found that they all showed excellent electromagnetic absorption effect.We explored the growth process,calcination process and the mechanism of electromagnetic absorption enhancement of these composites in details.By comparison,it is found that MOFs/SiC crystals appear as shrinking polyhedra after calcination in air.After calcined in argon,MOFs crystals are decomposed into many small particles.The enhancement of the absorption performance of electromagnetic wave should be attributed to the comprehensive effect of the decrease of the dielectric constant,the increase of the length-diameter ratio and the enhancement of the interface polarization.This study opens the way for the multidimensional construction of nanomaterials and the rational design and application of new electromagnetic absorption materials.(4)Networks constructed by metal organic frameworks(MOFs)and multiwall carbon nanotubes(MCNTs)for excellent electromagnetic waves absorptionThe composite material with high connectivity network structure has a good effect on the attenuation of electromagnetic radiation.In this study,firstly,we used multi-walled carbon nanotubes(MCNTs)with good electron transport capacity as connection lines and MOFs as connection points to construct three-dimensional network composites with efficient connection of MOFs/MCNTs.Then,MOFs/MCNTs composites with three-dimensional network structure were calcined under 500?argon atmosphere by controlling the temperature.Finally,we got the three-dimensional network structure of Co/C-MCNTs composites with high efficient electromagnetic wave absorption performance.After in-depth discussion and analysis,we believe that good impedance matching is an important reason to increase the absorption performance of electromagnetic waves,and the Co/C component from the MOFs derivative also increases the absorption of electromagnetic waves of the composite materials.This study has important guiding significance for the design of new MOFs matrix composites with structural characteristics.