| With the rapid development of communication technology and electronic equipment,electromagnetic wave pollution has become a serious problem.The radiation of electromagnetic wave not only interferes instruments and equipment,but also endangers human health.Electromagnetic wave absorbing materials can effectively absorb and reduce electromagnetic radiation.Metal-organic frameworks(MOFs)consisting of organic ligands and metal ions bonded with coordination bonds are a kind of crystal polymer with abundant microporous structure.According to the application and performance requirements,the metal ions,size and pore structure of crystal can be adjusted.Different nanocomposites of magnetic metal particles,dielectric oxides,porous carbon and their combinations can be derived from MOFs easily and simply.Thus,one material can possess two loss mechanisms of dielectric loss and magnetic loss.Meanwhile,the effective absorption bandwidth of each loss material can be united.Then the maximum effective absorption bandwidth can be improved.The research showed that by rationally designing MOFs derivatives,excellent electromagnetic wave absorption performances can be obtained.Based on the MOFs derivatives prepared through chemical synthesis,in this work,the electromagnetic wave absorption properties and mechanisms of different nanocomposites have been studied.The main research contents and results are summarized as follows:(1)The single metal ions(Zr)MOFs(UIO-66)was prepared by hydrothermal method.After the carbonization treatment under N2 protective atmosphere,high dielectric oxide ZrO2/C nanocomposites were derived from UIO-66.We studied the effect of the carbon with different graphitization degree on the conductivity and the effect of high dielectric oxide zirconium dioxide on dielectric loss.Based on the transmission line theory,the impact of two loss mechanisms on electromagnetic wave absorption performance were explored.And powder X-ray diffraction(PXRD),field emission scanning electron microscope(FE-SEM),high resolution transmission electron microscope(HR-TEM),X-ray photoelectron spectrometer(XPS),Raman spectroscopy,thermogravimetric analyzer(TG),and other testing methods were employed to characterize the intrinsic properties of the materials.According to the testing results,the nanocomposites showed the octahedral structure.With the increase of carbonization temperature,the graphitization degree rised as well,which caused an increasing conductivity.The electromagnetic wave absorption performance of the nanocomposites have been investigated.The results showed that the ZrO2/C nanocomposites carbonized at 800℃ exhibited excellent electromagnetic wave absorption performance.At 16.8 GHz,the minimum reflection loss value can up to-58.7 dB and the matching thickness was 1.5 mm.The maximum effective absorption bandwidth can reach 5.5 GHz.(2)Double metal ions(TiZr)MOFs(PCN-415)was prepared by two step hydrothermal method.After carbonization treatment under N2 protective atmosphere,double dielectric oxide Ti02/ZrTi04/C nanocomposites were synthesized.Bases on the above research,we studied the influence of the change of the dielectric loss by further adding high dielectric oxide on electromagnetic wave absorption performance.The results showed that the nanocomposites possessed a porous octahedral structure.However,the graphitization degree decreased with the increase of carbonization temperature,which can result in more defects.Porous TiO2/ZrTiO4/C nanocomposites carbonized at 800℃ showed excellent electromagnetic wave absorption performance.At 13 GHz,the minimum reflection loss can reach-67.82 dB with a matching thickness of 2.15 mm.And the maximum effective absorption bandwidth was 4.7 GHz.The excellent absorption performance benefited from the enhanced polarization loss.And the porous structure also can optimize the impedance matching.(3)NH2-UIO-66 was prepared by the hydrothermal approach.And then by in-situ growth method and the adsorption effect of surface functional groups of MOFs,Co2+were deposited on the NH2-UIO-66.After carbonization treatment under N2 protective atmosphere,Co/ZrO2/C nanocomposite were obtained.On the basis of the above two researches,both dieletric absorbing materials,we explored the effect of the magnetic particles on the electromagnetic wave absorption performance of nanocomposites.The results showed that porous Co/Zr02/C nanocomposites showed octahedral structure and the surfaces were decorated by metallic Co particles.ZrO2 particles were evenly distributed in the octahedral carbon matrix.Due to the introduction of Co metallic particles,matching thickness was reduced and the impedance matching was optimized.Also,The introduction of Co metallic particles can bring in magnetic loss.Thus,the nanocomposites exhibited excellent electromagnetic wave absorption performance.At 15.8 GHz,the strongest absorption can reach-57.2 dB with a matching thickness of 3.3 mm.Besides,an ultra wide maximum effective bandwidth of 11.9 GHz(6.1-18.0 GHz)was reached.According to the above series of studies,it can be concluded that carbon-based porous nanocomposites derived from MOFs can exhibit excellent electromagnetic wave absorption performance.By selecting dielectric metal oxides with different dielectric constant and magnetic metallic particles with different permeability,a variety of magnetic particles/high dielectric oxide/porous carbon nanocomposites can be obtained.Under the synergy effect of dielectric loss and magnetic loss,the electromagnetic wave absorption performance of the nanocomposites can be effectively controlled.It is beneficial to explore novel electromagnetic wave absorption materials. |
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