Synthesis Of Porous Materials From Layered And Chain Silicate Minerals And Basic Research On Their Applications

In recent years,both the widespread application of electronic devices and the rapid development of wireless communication aggravate the pollution of electromagnetic waves（EMWs）,which has become a top priority in urgent need of resolution,so as to make the normal operation of instruments and equipment,and protect the health of humans.Thus,EMWs absorption materials have been widely concerned by researchers because they can effectively attenuate EMWs.At present,obtaining high-performance absorber with strong absorption,thin thickness,lightweight,and broad bandwidth is the key point of research.Remarkably,carbon material is a kind of representative dielectric loss absorbing material due to the low density,tunable conductivity,rich resources and abundant morphologies,which is widely studied by researchers.In spite of this,due to the impedance mismatch,a single dielectric loss material may limit its application as high-performance EMWs absorbers.Combining it with magnetic loss materials is expected to improve impedance matching,thereby effectively improving the ability to absorb EMWs.In this paper,reduced graphene oxide（RGO）,metal-organic frameworks（MOFs）derived carbon and carbon nanotubes（CNTs）are used as carbon sources,which are combined with magnetic components of Fe₃S₄,Fe/Fe₃C（FeS/Fe₃C）,FeNi（Fe Co）,and Ni to construct composite absorbers.By adjusting the content and process conditions,improving its electromagnetic parameters,optimizing its impedance matching and attenuation capabilities,and finally meeting the requirements of an ideal absorber.The main contents of the paper are as follows:（1）3D flower-like Fe₃S₄ microspheres and quasi-sphere Fe₃S₄-RGO hybrid-architectures were successfully fabricated by a facile hydrothermal method,and the effects of filler loading,component content and microstructure on the EMWs absorption performance were studied.The results of morphology revealed that the single Fe₃S₄ was assembled into flower balls by many nanosheets,while in the case of Fe₃S₄-RGO composites,the quasi-sphere Fe₃S₄ was distributed on the RGO sheet.The electromagnetic parameters optimization of the single Fe₃S₄ and Fe₃S₄-RGO composites could be achieved by adjusting different filler loading and GO content,respectively,so as to achieve impedance matching.Among them,the reflection loss（RL）of the single Fe₃S₄ with 50 wt%filler loading could achieve-66.87 d B at 10.57 GHz for the thickness of 2.2 mm,and the effective absorption bandwidth（EAB,RL≤-10 d B）could reach 3.49 GHz.For the Fe₃S₄-RGO composites（40 wt%filler loading）,the minimum RL(RL_min)of FSR-1could reach-40.25 d B at 9.67 GHz with the thickness of 2.0 mm.In addition,the EAB of FSR-2 could reach 3.85 GHz at only 1.45 mm and the RL_min is-29.25 d B at 14.24 GHz.Consequently,the single Fe₃S₄ and Fe₃S₄-RGO composites are promising materials as a high performance and adjustable EMWs absorber.（2）FeS/Fe₃C/N-doped carbon nanorods（FCS）composites derived from metal-organic frameworks（MOFs）were developed via the carbonation-sulfidation strategy,and the influence of composition and structure on the EMWs absorption performance was further studied.By comparison with the carbonized products（Fe/Fe₃C/N-doped carbon composites）,the synergistic effect among multiple-components with heterogeneous interface and porous structure of FCS composites balance the impedance matching via reducing the complex permittivity,resulting in FCS composites excellent EMWs absorption performance.Among them,the FCS-2 composite exhibits an outstanding EMWs absorption ability,RL_min could reach-66.28 d B,and the broad EAB achieves 6.2 GHz at 1.88 mm,covering the entire Ku band.Hence,this work inspires the development of exploring novel high-performance EMWs absorption materials via the dual strategy of carbonation-sulfidation.（3）The rational construction of heterogeneous interface is conducive to the generation of interface polarization,and the composite design of dielectric loss and magnetic loss materials can effectively optimize the electromagnetic parameters,thus effectively improving the impedance matching.Herein,we adopt the solvothermal and pyrolysis process to fabricate the multicomponent and multidimensional composites containing the bimetallic FeNi or Fe Co@N-doped graphene layer/N-doped carbon nanorods/reduced graphene oxide（FeNi@NC/NCR/RGO or Fe Co@NC/NCR/RGO）derived from NH₂-bimetallic（FeNi or Fe Co）-MOFs/GO precursors.The excellent EMWs absorption performances are effectively achieved by adjusting the content of RGO and the filler loading.Compared with the case without RGO,the FeNi@NC/NCR/RGO composite（25 wt%filler loading）displays a strong RL of-52.61 d B at 14.44 GHz with a thin thickness of 1.65 mm,and EAB is 4.64 GHz.And the Fe Co@NC/NCR/RGO composite（20 wt%filler loading）displays a strong RL of-59.42d B at 17.8 GHz with a thinner thickness of 1.42 mm,and EAB is 5.28 GHz at 1.66 mm.Hence,this work provides a pathway to prepare the multicomponent and multidimensional composites with superior EMWs absorption.（4）Flake-assembled flower spherical Ni-MOF was synthesized by solvothermal method,and Ni nanoparticles and nitrogen-doped carbon-based composites（Ni@NC/NCNTs）were successfully synthesized under high temperature carbonization by introducing DCDA.The effects of composition and structure of Ni@NC/NCNTs on EMWs absorption properties were revealed by changing the carbonization temperature.It could be found that the Ni@NC/NCNT-600 composite exhibits good absorption performance in the C-band（4-8 GHz）.At a filling loading of 30 wt%,and its optimal RL reaches-34.22 d B at 4.88 GHz with a thickness of 5mm.In addition,an EAB of 4.2 GHz could be obtained at a relatively thin thickness of 1.8 mm.The reasonable adjustment of the filling loading would effectively improve the electromagnetic parameters and achieve a good impedance matching.Combined with the loss mechanism of conduction loss,interface polarization and dipole polarization,it leads to the excellent EMWs absorption performance.The optimal RL and EAB of Ni@NC/NCNT-800 composite could reach-56.05 d B at 3.32 mm thickness and 1.88 GHz at 25 wt%filling loading.Therefore,it provides some ideas for the development of high-performance carbon-based composites with three-dimensional conductive network structure.