Preparation And Electromagnetic Wave Absorption Properties Of Graphene/Magnetic Micro-Nanoparticle Composites

With the rapid development of electromagnetic wave(EM)used in civil,commercial and military fields,severe EM interference(EMI)has become a pollution problem,which is not only interrupting the operation of electronic devices,but also threating to human health.Therefore,the EM wave absorbing materials are highly demanded for solving expanding EMI problems.At the same time,EM wave stealth technology is also closely related to the development of modern weapons and equipment,and is one of the key technologies for modern war defense and victory.To date,the high performance EM wave absorbing materials need to satisfy the requirements of thin thickness,wide absorption bandwidth,lightweight and strong absorption.Compared to other EM absorbing materials,graphene exhibits many exceptional properties including light weight,large specific surface area,good electrical conductivity,good corrosion resistance,high thermal stability and high chemical stability,and has caused enormous attention.However,the EM wave absorption property of pure graphene is very poor because of its attenuation toward EM wave only dependent on the dielectric loss as well as its poor impedance matching characteristic.The graphene can be used as a substrate for growth of heterogeneous particles and the synergistic effect between graphene and particles is contribute to improving its absorbing performance.In this paper,the magnetic materials and graphene were compounded to construct a new type of absorbing composite material from the perspectives of nano composite,morphology and covalent bond,so as to make it have both dielectric loss and magnetic loss,improve impedance matching and enhance the absorbing performance.Relevant research contents are as follows:(1)Ferromagnetic graphene nanocomposites with ZnO nanorods and Fe₃O₄ nanoparticles co-decorated have been successfully synthesized via a facile solvothermal process in combination with the co-precipitation route,and the EM wave absorption performance was reported.The maximum reflection loss of the RGO/Fe₃O₄/ZnO nanocomposites reached-57dB at 13.5 GHz with a matching thickness of only 2 mm.The effective absorption bandwidth with the R_L less than-10 dB(90%attenuation of electromagnetic wave)could be tuned to10.8 GHz(5.9-16.7 GHz)at the absorber thickness of 1.5-4 mm,which coverd the whole X band(8-12 GHz).(2)Hybrid RGO/CoFe₂O₄/ZnS nanocomposites were successfully synthesized via a facile hydrothermal process in combination with the co-precipitation route.The ZnS quantum dots and CoFe₂O₄ nanoparticles with an average diameter of 3-8 nm and 10-20 nm,respectively,were homogeneously anchored on graphene sheets.The EM wave absorption properties of RGO/CoFe₂O₄/ZnS nanocomposites were significantly improved compared with RGO/CoFe₂O₄ nanocomposites,with the maximum reflection loss as high as-43.2 dB at only 1.8 mm and the maximum absorption bandwidth(<-10 dB)of 5.5 GHz(from 10.2 to15.7 GHz)at 2 mm.And the absorption bandwidth(<-20 dB)was up to 6.3 GHz with a thickness in the range of 1.5-2.5 mm.Moreover,the absorption bandwidth(<-10 dB)almost covered the whole frequency range(from 3.6 to 18.0 GHz)with the thickness range of 1.5-5mm.(3)RGO/CoFe₂O₄/SnS₂nanocomposites have been successfully synthesized by two-step solvothermal processes,and CoFe₂O₄ and SnS₂ nanoparticles with both diameters about 5-10nm were well dispersed on the surface of graphene.Compared with RGO/CoFe₂O₄composites,the as-prepared RGO/CoFe₂O₄/SnS₂composites exhibited excellent electromagnetic wave absorption properties in terms of both the maximum reflection loss and the absorption bandwidth.The maximum reflection loss of RGO/CoFe₂O₄/SnS₂composites was-54.4 dB at 16.5 GHz with thickness of only 1.6 mm and the absorption bandwidth with the reflection loss below-10 dB was up to 12 GHz(from 6 to 18 GHz)with a thickness in the range of 1.5-4 mm.(4)?-Fe₂O₃@SiO₂nanoparticles have been successfully enveloped in graphene nanosheets/thorns-like polyaniline matrix(RGO/thorns-like PANI/?-Fe₂O₃@SiO₂nanocomposites)by some facile strategies.The measured electromagnetic parameters indicated that the interfacial polarization,the charge transfer,the multiple reflections and scatterings,the Debye dipolar relaxation processes,the magnetic loss,the quarter-wavelength matching and the well-matched characteristic impedance all played significant roles in improving the electromagnetic wave absorption performance.The maximum reflection loss of RGO/thorns-like PANI/?-Fe₂O₃@SiO₂ nanocomposites reached-50.06 dB at 14.4 GHz with a matching thickness of only 2.3 mm,and the absorption bandwidth with reflection loss less than-10 dB was in the 4-18 GHz range for the absorber thickness of 1.5-5.5 mm.Moreover,the adding quantity of nanocomposites in the paraffin matrix was only 16.7 wt%.(5)The hollow Zn_xFe_3-xO₄@porous MnO₂/r GO conductive network composites were synthesized by solvothermal-hydrothermal-hydrothermal reactions.The special three-in-one structure of hollow,core-shell and porous was sufficiently conducive to the absorption of electromagnetic wave by composites.Compared with binary hollow Zn_xFe_3-xO₄@porous MnO₂ and r GO/hollow Zn_xFe_3-xO₄composites,the ternary composites showed the excellent electromagnetic wave absorption performance in both reflection loss and bandwidth.The maximum reflection loss of-50.6 dB occured at 8.96 GHz and effective bandwidth below-10dB could shift from 3.6 GHz to 18 GHz with a thickness of 1.5-5.5 mm.The glorious absorption properties mostly derived from synergistic effect of magnetic and dielectric loss.(6)A novel multiple-phase nanocomposites of core-shell CoNi alloy@C nanoparticles uniformly implanted on graphene conducting network were prepared via combining hydrothermal and liquid phase reduction.The core-shell CoNi alloy@C nanoparticles were uniformly dispersed over graphene nanosheets.The abundant conductive network of reduced oxide was favorable for CoNi alloy@C nanoparticles insertion.Compared to single CoNi alloy and CoNi alloy@C,the ternary CoNi alloy@C/r GO nanocomposites revealed a remarkable increase in microwave absorption.The maximum reflection loss achieved-62.4dB at 7.84 GHz,and the effective bandwidth of reflection loss below-10 dB was up to 14.4GHz.Meanwhile,through calculation of absorption efficiency,it could be obtained that the nanocomposites had a best absorption performance at 3.3 mm and the efficiency value was24.88 dB·GHz/mm.(7)A novel hierarchical composites for coupling thistle-like CoNi with dielectric Ag decorated graphene as high performance microwave absorber has been synthesized combining hydrothermal and liquid phase reduction reaction.Due to the unique flower structure and good synergistic effect of dielectric loss and magnetic loss,thistle-like CoNi@dielectric Ag decorated graphene composites have showed glorious microwave absorption intensity and frequency width.The maximum reflection loss of-61.9 dB could be gained at 6.96 GHz.In addition,the corresponding effective bandwidth with reflection loss less than-10 dB was 5.6GHz ranging from 12.4 to 18 GHz at only 1.67 mm thickness.(8)Unique covalently bonded cobalt ferrite(CoFe₂O₄)/graphene nanocomposites were successfully fabricated via an amino-ester-amide reaction process.Compared to non-covalently bonded nanocomposites,the covalently bonded CoFe₂O₄/graphene nanocomposites had outstanding electromagnetic wave absorption properties.We found that the maximum reflection loss value reached at-55.2 dB and the absorption bandwidth with reflection loss below-10 dB was about 5.4 GHz at 1.7 mm of thickness.The efficiency was attributed to the introduction of amide bonds in the nanocomposites.As a stable carrier channel,amide bonds could promote the migration rate of electrons and binding degree between CoFe₂O₄ and graphene nanosheets,which provided a crucial impact on electromagnetic parameters and polarization modes of materials,thus improving the absorption capacity of electromagnetic waves.