| In recent years,with the high frequency use of electronic products,electromagnetic wave radiation has become an unavoidable problem.Therefore,the research on high-performance electromagnetic wave absorbing materials has become a hot topic for researchers.Carbon materials with low density and high permittivity are often used as light absorbing materials in electromagnetic wave absorption field.In addition,the composites derived from metal organic frameworks(MOFs)are also used in electromagnetic wave absorption because of their porous structure and large specific surface area.This paper mainly investigated the preparation and electromagnetic wave absorption properties of zeolitic imidazole frameworks(ZIFs)ZIF-67 and ZIF-8 derivatives and multi-walled carbon nanotubes(MWCNTs)composites with MOF structure.(1)Firstly,the Co-based zeolitic imidazolate framework ZIF-67 and MWCNTs were selected as the precursor materials.By adjusting the proportion between the two materials,ZIF-67/MWCNTs compsites with different molar ratios were prepared.The products were named 500-1 500-2 and 500-3 samples(different molar ratios of MWCNTs)after thermal decomposition at 500? in the argon atmosphere.The analysis and calculation show that 500-3 sample has the best absorbing performance because of its good impedance matching characteristics.The thermal decomposition products of sample 3 with the optimum molar ratio of MWCNTs to ZIF-67 at three different temperatures(500?,600? and 700?)were analyzed.The results showed that the obtained composites are different at different temperatures.The composites of 500-3 and 600-3 samples were all CO3O4/MWCNTs,and the composites of sample 700-3 were CoO/MWCNTs.The properties of the obtained composites at different thermal decomposition temperatures are also different.The obtained MWCNTs@carbonaceous CoO composites at 700? exhibits good absorbing properties.The optimal value of reflection loss(RL)can reach-50.2 dB,the bandwidth less than-10 dB is 4.32 GHz(12.32-16.64 GHz),and the matching thickness is 1.84 mm.Through the study and analysis of the absorption mechanism of electromagnetic wave,it is shown that the high absorption performance of electromagnetic wave is due to the coordination between the two loss mechanisms,the good impedance matching and the synergistic effect between CoO nanoparticles and MWCNTs.(2)Secondly,using MWCNTs and ZIF-8 as precursors,samples 600-1,600-2 and 600-3(different MWCNTs content)were fabricated by wet chemical method and pyrolysis(600?)to form nanoporous carbon(NPC)composites.The results show that the electromagnetic wave absorbing properties of sample 600-1 are poor,while those of 600-2 and 600-3 samples are similar.By comparison,we found that the impedance matching of sample 600-3 was better than that of sample 600-2.The thermal decomposition products 600-3,700-3 and 800-3 of sample S3 at three different temperatures(600?,700? and 800?)were analyzed.The results show that the sample 600-3 is ZnO@NPC@MWCNTs.With the increase of pyrolysis temperature,700-3 and 800-3 samples are both Zn@NPC@MWCNTs.Good matching impedance and strong attenuation give sample 800-3 an optimal RL value of-61.17 dB and an effective band(<10 dB)of 4 GHz(8-12 GHz)covering the entire X-band at a matching thickness of 2.75 mm,which benefits from multiple reflection and absorptin of electromagnetic wave in nanoporous carbon.(3)Finally,the fixed molar ratio of Co-Zn-ZIF was combined with three different mass MWCNTs,and nine samples were obtained by thermal decomposition at three different temperatures(600?,700? and 800?),which were named as 600-1,600-2 and 600-3;700-1,700-2 and 700-3;800-1,800-2 and 800-3,respectively.The results show that the thermal decomposition composites at 600? were Co3ZnC,but the pyrolysis products are the same at 700? and 800?,all of which are Co-Zn@NPC@MWCNTs.By exploring the properties of 800-3 samples with different filling loading(10 wt%515 wt%,20 wt%and 25 wt%)in paraffin wax,the results show that the absorber has the best electromagnetie wave absorbing performance when the filling content of the composites is 15 wt%.The maximum RL value can reach-51.58 dB at 8,08 GHz,the corresponding matching thickness is 3.0 mm,and the effective absorbing bandwidth can get up to 6.56 GHz(7.2-13.76GHz).The results show that the porous structure,higher permeability,the synergistic interaction between Co and Zn and the better impedance matching characteristics enhance the electromagnetic wave absorption performance of Co-Zn@NPC@MWCNTs composites.In this paper,carbon-based electromagnetic wave absorbing composites with MOF structure were fabricated based on the combination of MOFs(ZIF-67,ZEF-8 and Co-Zn-ZIF)and MWCNTs.The research shows that strong attenuation performance and good matching impedance characteristics are two important conditions for absorbing materials to possess high-efficiency absorbing performances,which provides a reference for further preparation of high-efficient electromagnetic wave absorption composites. |
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