Study On The Preparation And Absorbing Properties Of Metal-organic Framework Materials And Derivatives

With the development and application of electromagnetic wave technology,the deep integration of electromagnetic wave and equipment in the fields of communication,television broadcasting,radar and navigation has greatly improved people’s production and life,but also brought increasingly serious problems such as electromagnetic wave interference and pollution,which has caused great harm to human life.At the same time,due to the continuous development of radar and other detection technologies in the military field,the"stealth"capability of weapons and equipment has been put forward higher and higher requirements.Nowadays,the exploration and research of high-performance new electromagnetic wave absorbing materials has gradually become a focus of material researchers.Absorption materials convert the energy of the incident electromagnetic wave into heat energy or other forms of energy through different ways of loss and then consume.Ferrite and magnetic material such as metal particles Fe,Co,Ni possessing strong saturation magnetization,and the magnetic loss and power loss,in terms of new absorbing materials has the potential research value,but its density is larger,the low level of impedance matching,effective absorbing band narrow,no corrosion and other disadvantages limit its wide application.In recent years,carbon nanomaterials have been favored by scientists and technicians as ideal electromagnetic absorption materials due to the advantages such as light weight and excellent electrical loss performance.However,carbon materials have many defects such as lack of magnetism,poor impedance matching level and single loss mechanism,so there is a large gap between carbon materials and ideal new electromagnetic absorption materials.In order to overcome the deficiency of single component materials and give full play to the synergistic effect of dielectric loss and magnetic loss on electromagnetic wave absorption.This study uses the simple hydrothermal method to prepare metal organic skeleton（metal organic frameworks,MOFs）materials,and then MOFs are pyrolyzed as a precursor at different pyrolysis temperatures to get different degree of graphitization carbon composite material,realizing the coordination of loss mechanism and impedance matching of composite materials,eventually get the"thin""light""wide""strong"of new absorbing materials.The main research contents of this paper are as following:（1）Using hydrothermal and pyrolysis method to synthesis Fe/C nanocomposites with hollow structure,the Fe-MOFs were synthesized firstly by the solvent method,then Fe-MOFs materials were carbonized as the precursor in N₂,respectively at 600℃,700℃,800℃,900℃different temperature.The precursors and pyrolysis products were analyzed by crystal structure analysis,morphology analysis,Raman spectroscopy analysis and thermogravimetric curve analysis,and the test results show the composites have a uniform hexagonal rod crystal structure,and the graphitization degree increases with the increase of pyrolysis temperature.Then Fe/C nanocomposites were mixed with polyvinylidene fluoride（PVDF）to obtain flexible composites.After the tablets were compressed and prepared,the vector network analyzer（VAN）was used to test the dielectric constant and permeability of the samples in the range of 2-18GHz,and the reflection loss was calculated according to the transmission line theory.The test results show that when the pyrolysis temperature is 700℃and the filling amount is 20wt%,the absorbing intensity reaches-41d B and the effective bandwidth is 4GHz.（2）First,the bimetallic（Fe/Co）MOFs were prepared by solvothermal method,and the products were used as precursors for pyrolysis in the temperature range of 600～900℃in the protective atmosphere of N₂ to prepare the derivatives Fe/Co/C composites.SEM results show that the overall morphology of Fe/Co/C composites presents a uniform one-dimensional hexagonal bar crystal structure.The XRD test results show that the pyrolysis temperature has a great influence on the composition and graphitization degree of the derivatives.The higher the temperature,the higher the graphitization degree will be,and then the electromagnetic parameters of the absorbing materials will be affected.Therefore,the electromagnetic absorption performance of the derivatives can be adjusted by adjusting the pyrolysis temperature.The absorbing performance of the samples with different filling ratios was tested by vector network analyzer.When the pyrolysis temperature was 850℃and the filling amount was 5wt%,the optimal reflection loss value was-44d B,and the effective bandwidth reached 5.4GHz.（3）MOFs with three metal ions were prepared by a mild hydrothermal method as precursors,and then the composite material with ferromagnetic particles and porous carbon was prepared by pyrolysis at 800℃with N₂ as the protective gas.SEM test results show that the MOFs material presents a uniform needle-like spherical structure,and the porous structure characteristics of MOFs precursors can also be transferred to the sintered products to a certain extent,which is conducive to the multiple reflection loss of microwave.Under the dual loss mechanism of dielectric loss and magnetic loss,the optimal reflection loss value was-18.8d B,and the effective bandwidth was 4.72GHz.