Preparation And Microwave Absorbing Properties Of Carbon Based Composite Materials Drived From MOFs

In recent years, carbon-based material has drawn great attention as promising lightweight microwave absorbing material due to its low density, strong electromagnetic wave attenuation abilities and several satisfying properties. In the thesis, a novel lightweight microwave absorbing material has been prepared through calcining a kind of zeolitic imidazolate framework(ZIF-67), which can be easily synthesized by an aqueous approach. In order to improve the impedance match behavior of pure Co@NPC(magnetic Co nanoparticles embedded in nanoporous carbon matrix) through carbonization of ZIF-67, three methods were used to improve the microwave absorption performance.(1) A novel Fe-Co nanoparticles embedded in nanoporous carbon composite(Fe-Co/NPC) was synthesized via in situ carbonization a pretreated percursor, Fe3O4 nanoparticles encapsulated in ZIF-67. The molar ratio of Fe/Co in the final composites significantly depends on the encapsulated content of Fe3O4 in ZIF-67. The results showed that the magnetic and impedance matching properties have been improved a lot due to the as-obtained Fe-Co alloy in the composites, which was related to the Fe3O4 in the precursors. A maximum reflection loss(RL) of-21.7 dB with the thickness of 1.2 mm, and a broad effective absorption bandwidth(RL <-10 dB) of 5.8 GHz from 12.2 to 18 GHz can be obtained in the sample Fe-Co/NPC-2.0.(2) Furthermore, two core-shell structure materials Co@NPC@TiO2 and C-ZIF-67@TiO2(derived from carbonation of ZIF-67@TiO2) were prepared through in situ hydrolysis of tetrabutyl titanate. These materials not only maintain the advantages(low-density, strong attenuation) of Co@NPC, but also overcome the unsatisfying impedance match performance. A maximum reflection loss(RL) of-51.7 dB at with the thickness of 1.65 mm and-31.7 dB at 1.5 mm can be gained for C-ZIF-67@TiO2-2.0 and Co@NPC@TiO2-1.2, respectively.(3) Finally, in order to obtain high-efficiency microwave absorber, a structure of electromagnetic wave transparent materials embedded in the pores of microwave absorbing materials has been constructed. In this paper, CuO nanoparticles encapsulated in porous carbon composites(CuO @ NPC) were synthesized via calcining the porous carbon(obtained by the carbonization of ZIF-67) filled with adsorbed copper nitrate under suitable temperature. It has been proved that CuO @ NPC composite, which can be obtained by calcining in 300℃, owned much better impedance matching behavior than the porous carbon drived from ZIF-67. The CuO @ NPC composites show a maximum reflection loss(RL) of-57.5 dB with the thickness of 1.55 mm at a frequency of 14.9GHz and a broad absorption bandwidth for RL <-10 dB of 4.7 GHz from 13 to 17.7 GHz.In conclusion,as-prepared carbon-based lightweight absorbing materials drived from MOFs not only keep the advantages including low-density and strong attenuation, but also improve the impedance matching performance of Co@NPC. This study may shed light on the research about the lightweight microwave absorbing material derived from MOFs.