Design And Preparation Of ZIF-based Composites And Property Of Electromagnetic Wave Absorption

Electromagnetic wave(EMW)absorption materials are the core of radar stealth technology.With the development of anti-radar stealth technology,to improve the ability for survival,defense penetration and deep attack capability of weapons and equipment,EMW absorption materials not only require wide frequency band and high absorption intensity,but also require light weight,thin surface and good thermal stability.Zeolitic imidazolate frameworks(ZIF)materials are formed by complexation of metal ions and organic imidazole esters through cross-linking interaction with the advantages of good thermal stability,large specific surface area and high porosity.ZIF can be directly carbonized at high temperature to form a metal or metal oxide/nano porous carbon composite,which has the potential to become a highly efficient EMW absorber.However,a large number of voids are not conducive to carrier migration,which can lead to a low dielectric constant and inferior attenuation performance.Therefore,how to combine ZIF materials and high dielectric loss material through appropriate technical means and prepare EMW absorption composite with multiple electromagnetic loss mechanism and special structure has important research value.Starting from the material structure design,this thesis combines ZIF materials with highdielectric light carbon materials(graphene oxide(GO),polydopamine(PDA),polypyrrole(PPy),polyaniline(PAN))to optimize electromagnetic parameters of the ZIF-based composite materials can improve the EMW absorption capacity and achieve the goal of "wide,thin,light and strong".CoC-rGO hybrids were prepared as EMW absorber.GO with a large amount of carboxyl groups on the surface was synthesized.ZIF-67 was introduced between GO layers by electrostatic forces,and the final product CoC-rGO was obtained by calcination.By adjusting the ratio of GO,electromagnetic parameter of CoC-rGO can be optimized.It was found that when the mass ratio m[GO]/m[Co(NO3)2·6H2O]=0.5/2.91 and a consisting of 10 wt%for CoCrGO-2 in the paraffin matrix provided excellent EMW absorption performance.The minimum reflection loss(RLmin)is-44.77 dB at 12.14 GHz with the thickness of 2.1 mm and the effective bandwidth(RL?-10 dB)can reach up to 5.2 GHz at the thickness of 1.8 mm.The introduction of rGO increased the conductance loss and improved the dielectric properties.We employ self-etching template method to prepare an ideal EMW absorber,which is hollow dodecahedral carbon capsules embedded with Ni-Co alloy particles.The hollow dodecahedral PDA capsules are constructed by the Ni(OH)2/ZIF-67 template automatically etched off during in situ polymerization of Dopamine-HCl.N-doped carbon capsules(NCs)embedded with Ni-Co alloy particles(named as Air@NCs€Ni-Co)are obtained after the thermal treatment of Ni(OH)2/ZIF-67@PDA.The EMW absorption performance of Air@NCs€Ni-Co has been tuned by different contents of Ni(OH)2 and calcination temperature.When the contents of Ni(OH)2 is 0.5 mL at 700?,RLmin value is-36.5 dB at 14.77 GHz with a thickness of 2.2 mm.The effective bandwidth can reach up to 6.55 GHz(from 11.45 to 18 GHz)with a thickness of 2.3 mm,which covers the whole Ku band with 25 wt%filled.Core-shell structure ZIF-8 derived ZnO/nanoporous carbon coated by polypyrrole(ZnOC@PPy)dielectric composite EMW absorption materials have been fabricated through hydrothermal method and in-situ oxidation polymerization.By changing the pyrolysis temperature of ZIF-8 and addition of pyrrole,the best conditions are finally presented at the amount of 0.4 mL pyrrole(per 0.1g ZnOC)and 700?(ZIF-8 heating temperature).Its RLmin reaches to-76.31 dB surprisingly at 14.85 GHz at 14.85 GHz with the thickness of 2.17 mm,and the effective absorption bandwidth can reach 6.38 GHz with the thickness of 2.25 mm,covering the whole Ku band with only 15wt%filled.Introduce magnetic layer to ZIF-8 and change the outer shell to synthesize a novel ternary core-shell structured ZnOC@CoC@PAN as an EMW absorber.ZnOC@CoC@PAN was successfully fabricated by calcining ZIF-8@ZIF-67 and covering with PAN.EMW absorption performance were adjusted by controlling the amount of aniline.It was found that when the coating amount of aniline is 0.5 mL(per 0.1g ZnOC@CoC),the RLmin is-50.62 dB at 13.66 GHz with the thickness of 2.05 mm and the maximum effective absorption bandwidth is 5.86 GHz with 25 wt%filled.The ternary core-shell structure of ZnOC@CoC@PAN forms multiple interface polarizations,and the PAN coated with the outer layer provides conductivity loss,which can improve the ability to attenuate EMW.In summary,the simple and green method were adopted to combine the ZIF derivatives with high dielectric materials to prepare a series of EMW absorption composite successfully.All the sample have good EMW absorption capabilities.It overcomes the weakness of the low dielectric constant of ZIF materials and the large amount of filling required to achieve efficient EMW absorption.It provides a new idea to further modify the ZIF materials in EMW absorption field.