Preparation Of MCo₂O₄（M=Ni,Zn） And ZIF-67 Composites And Investigation Of Electromagnetic Wave Absorption Properties

As the application environment of electromagnetic wave absorbing materials becomes more and more complex,the research and development of single absorber materials cannot meet the needs in practice.Using two or more kinds of complementary or enhanced materials to construct multi heterojunction composites has become a hot research topic in the field of microwave absorption.Among many monomeric dielectrics and magnetic dielectrics,magnetic bimetallic oxides are good dielectrics,usually with lamellar structure,while metal organic framework derivatives are good magnetic dielectrics,usually with hollow polyhedral structure formed by nitrogen doped carbon coated magnetic metal nanoparticles as structural units.In order to realize the preparation of multi-component and multi-level composite heterojunction materials,we composite the two materials and study the reconstruction of heterojunction interface at different annealing temperatures.The multi-layer structure of materials can reduce the density of materials,broaden the effective bandwidth,and obtain light absorbing materials with strong broadband absorption.This design strategy of multi-component and multi-level structure is the development orientation of lightweight and broadband absorbing materials.In this work,dodecahedral metal organic framework ZIF67 and Tremella like NiCo₂O₄heterogeneous interface composites were fabricated by hydrothermal method combined with annealing process.The structural changes and electromagnetic wave absorption properties of the composites were systematically studied at different annealing temperatures.The main research contents are as follows:（1）The NiCo₂O₄@ZIF67 composites were annealed in argon atmosphere with the interval of 50℃pyrolysis temperature within 350-550℃.The NiCo₂O₄@ZIF67 transform self-assembly into Co O@N/C,Co O@N/C-Co/Ni-NiCo₂O₄,Co/Ni@N/C multi-heterostructure composites.The results show that,with filling degree of the samples is 30%,the reflection loss（RL）of Co O@N/C composite is-77.46 dB,effective absorption bandwidth（EAB）is3.15 GHz,and matching thickness is 4.2mm.The RL of Co/Ni@N/C is-61.73 dB and EAB is 2.07 GHz.In particular,the RL of Co O@N/C-Co/Ni-NiCo₂O₄ not only is-52.45 dB at14.77 GHz,but also 5.3 GHz for EAB when the matching thickness is 1.66 mm.（2）The ZnCo₂O₄@ZIF67 composites were annealed in argon atmosphere with interval of50℃pyrolysis temperature in the range of 400-650℃.The ZnCo₂O₄@ZIF67 transform self-assembly into ZnCo₂O₄@Co O@N/C,Zn O-Co@N/C,Co₃Zn C-Co@N/C multi-heterostructure composites.The results show that,with filling degree of the samples is 30%,the RL of ZnCo₂O₄@Co O@N/C composite is-17.82 dB,and the EAB with thickness of2.77 mm is 3.77 GHz.The RL of Zn O-Co@N/C is-62.7 dB,and the EAB with thickness of 2 mm is 5.75 GHz.The RL ofCo₃Zn C-Co@N/C is-59.18 dB,the EAB is 5.79 GHz with thickness of 1.97 mm.It is found that the NiCo₂O₄@ZIF67 and ZnCo₂O₄@ZIF67 composites exhibit different phase transition processes at different annealing temperatures.The original heterogeneous interfaces are reconstructed and self-assembled to form a variety of heterogeneous interfaces,which can effectively improve the electromagnetic wave absorption properties of the composites.After pyrolysis,the structure of the composite is reconstructed,and the formation of multiple heterointerfaces promotes the enhanced synergistic effect among conductivity loss,strong dipole polarization,multi-interface polarization,and excellent impedance matching.This research work will provide a novel design idea for the construction of multi heterogeneous interface composites.