Preparation And Microwave Absorbing Properties Of Onedimensional Magnetic Flowerlike Composites

In order to solve the problem of electromagnetic wave pollution caused by the surge of electronic communication equipment,it is of great significance to explore high-performance electromagnetic wave absorbing materials(also known as microwave absorption materials).In recent years,the research hotspot is the development of reasonable material configurations and effective preparation methods to obtain high-performance microwave absorbers to meet the needs of"thin,wide,light,and strong".Due to the limitations of microwave absorption materials with a single loss mechanism,such as poor impedance matching and narrow absorption band,microwave absorption materials with multiple loss mechanisms are currently the mainstream of research.Shape and structure control are effective strategies for adjusting the absorbing characteristics.One-dimensional structures have received extensive attention due to the high aspect ratio and shape anisotropy.Therefore,three one-dimensional flower-like composite microwave absorption materials are designed and prepared in this work.Their microstructure,phase composition and magnetic properties are characterized and electromagnetic parameters and microwave absorption performance are studied.The main research contents are given as follows:(1)ZnFe₂O₄ nanoparticles prepared by solvothermal method were used as the assembly unit,and the SiO₂ layer wrapped the surface through the St(?)ber method induced by an external magnetic field,thus one-dimensional ZnFe₂O₄@SiO₂ nanochains were successfully obtained.Afterwards,the carbon layer and Ni O nanosheets were coated on the outside to obtain one-dimensional flower-like ZnFe₂O₄@SiO₂@C@Ni O(ZSCN)nanochains.Finally,ZSCN nanochains were composited with reduced graphene oxide(RGO)to obtain ZnFe₂O₄@SiO₂@C@Ni O/RGO composite material.The introduction of RGO nanosheets enables the composite material to achieve better impedance matching,and the functional groups and defects on the RGO nanosheets enhance the dipolar polarization relaxation.In addition,the one-dimensional and flower-like structure of the ZSCN nanochains extend the loss path of microwaves.The microwave absorption test results showed that the sample containing 50 wt%ZSCN/RGO composites exhibits the optimal microwave absorption performance.The minimum reflection loss value can reach-66.38 dB at 9.58 GHz with a thickness of 2.45 mm,and the corresponding effective absorption bandwidth can be up to3.44 GHz(8.12-11.56 GHz).(2)One-dimensional Ni nanowires were fabricated through the wet chemical reduction method induced by an external magnetic field,and then the phenolic resin layer was coated on the outside of the Ni nanowires by in-situ polymerization,and Co(OH)₂nanosheets were grown on the outside of the phenolic resin layer by the oil bath reflow method to obtain one-dimensional Ni@phenolic resin@Co(OH)₂ nanowires.Afterwards,one-dimensional flower-like Ni@Co₃O₄ nanowires were obtained by one-step heat treatment in an air atmosphere.Finally,Ni@Co₃O₄ nanowires were fully mixed with graphene oxide suspension and hydrothermally reacted to obtain Ni@Co₃O₄/RGO composite material.The one-dimensional structure and flower-like structure can induce multiple reflection/scattering of microwaves,and the interface between them can cause interface polarization.In addition,the introduction of RGO nanosheets strengthened the dipole polarization and improved impedance matching,thereby improving the microwave absorption performance.The microwave absorption test results showed that the sample containing 35 wt%Ni@Co₃O₄/RGO composites has the optimal microwave absorption performance.The minimum reflection loss can reach-60.0 dB at 10.38 GHz and the corresponding absorption bandwidth of 3.36 GHz(8.88-12.24 GHz)is achieved at the thickness of 2.30 mm.Besides,the maximum effective absorption bandwidth of 4.62 GHz can be obtained at the thickness of 1.6 mm.(3)One-dimensional?-Fe₂O₃ nanofibers were directly prepared by electrospinning technology,and then a polydopamine layer was coated on the outside through in-situ polymerization,and carbonized and reduced in a hydrogen/nitrogen mixed atmosphere to obtain Fe₃O₄/Fe@C nanofibers in one step.Finally,the MoS₂ nanosheets were covered by hydrothermal method on the outside of the nanofibers to obtain Fe₃O₄/Fe@C@MoS₂nanofibers.Comparing the electromagnetic parameters and microwave absorbing properties of Fe₃O₄/Fe@C nanofibers and Fe₃O₄/Fe@C@MoS₂ nanofibers,it is found that the introduction of MoS₂ nanosheets improves the impedance matching of the material and enhances the dielectric loss,and further enhance microwave attenuation.The sample containing 50 wt%one-dimensional flower-like Fe₃O₄/Fe@C@MoS₂ nanofibers has the optimal microwave absorption performance.The minimum reflection loss can reach-53.79 dB at 11.12 GHz and the corresponding absorption bandwidth of 4.4 GHz(9.62-14.02 GHz)is achieved at the thickness of 2.24 mm.In summary,three one-dimensional magnetic flower-like microwave absorbing materials with core-shell structure were prepared in this article and their microwave absorbing properties were systematically investigated.The results show that the prepared microwave absorption materials have good application prospects.This article provides new ideas and technical supports for the preparation of high-efficiency one-dimensional microwave absorption materials in the future.