Investigation Of Three-dimensional Penetrating Multi Interface Organic Frameworks For Enhanced Microwave Absorption Performance

With the advent of the electronic information era,electromagnetic wave also shows a health threat to the human living environment.Microwave absorbing materials effectively solve such electromagnetic pollution problems.Traditional absorbers often have narrow effective absorption bandwidth and poor maximum reflection loss performance due to the single component and simple structure.Currently,the noval design of multicomponent core-shell structures with enhanced reflection loss and broad absorption band have become the focus of current research.In this thesis,combined with the structural advantages of covalent organic skeletons（COFs）materials such as large specific surface area,light density,and good chemical stability,through reasonable design of experimental conditions and preparation processes,we designed core-shell structures of Co/C@COFs and FeSiAl@（CoFe₂O₄/C）@COFs to achieve better microwave absorption performance.The specific work of the thesis is as follows:1.Preparation of Co/C hybrid structures.The morphology and structure of precursor ZIF-67 were regulated by adjusting experimental parameters.With the increase of the amount of 2-methylimidazole reactant added,the particle diameter of ZIF-67 precursor showed a trend of increasing and then decreasing.The dodecahedral structure was deformed.After carbonization,the Co/C composite exhibits agglomeration.The synthesis of Co/C hybrid structures laid the foundation for the following experiments.2.Preparation process and microwave absorbing properties of Co/C@COFs with multi interface structures.Based on the Schiff base reaction,two amide bonded covalent organic frameworks（Tp Pa and TAPB-PDA）were designed to coat Co/C to form core shell structure absorbing materials.The covalent organic skeletons（COFs）can block the conductive networks of carbon nanotubes on Co/C hybrid structures to optimize impedance matching characteristics.In addition,a large number of heterogeneous interface structures are conducive to creating a large number of interfacial charge layers and defect vacancies.Compared to Co/C,Co/C@TAPB-PDA The maximum reflection loss achieved at 8.8 GHz is-50.6 d B.By adjusting the thickness of the absorbing coating to 0.5～5 mm,its effective absorption bandwidth can cover 3.5～18.0 GHz（C～Ku frequency band）to meet the adjustable absorption frequency band.3.Enhanced microwave absorbing performance of FeSiAl based multilayered core-shell structures.FeSiAl material has excellent soft magnetic properties.Combining ZIF-67 and COFs organic skeleton as modified materials,a FeSiAl@（CoFe₂O₄/C）@COFs composite material was designed and prepared.After the precursor ZIF-67 was coated and carbonized,a cobalt ferrite/carbon coating was formed on the surface of FeSiA.Then,the COFs material was coated on the surface by solution method to form a multi-shell structure.FeSiAl@（CoFe₂O₄/C）@COFs achieve a maximum reflection loss of-51.3 d B at 9.2 GHz,an effective absorption bandwidth of 3.3 GHz,and a coverage of 8.0 to 11.3GHz.A large number of heterogeneous interfaces and defects are formed between FeSiAl,CoFe₂O₄,C,and Tp Pa,which is conducive to enhancing the interfacial polarization and dipole polarization of the material.At the same time,multiple reflection and scattering of microwave can be achieved between multi-layer core shells,enhancing microwave loss ability.