Multifunctional MXene/C Aerogels for Enhanced Microwave Absorption and Thermal Insulation

Two-dimensional transition metal carbides and nitrides(MXene)have emerged as promising candidates for microwave absorption(MA)materials.However,they also have some drawbacks,such as poor impedance matching,high self-stacking tendency,and high density.To tackle these challenges,MXene nanosheets were incorporated into polyacrylonitrile(PAN)nanofibers and subsequently assembled into a three-dimensional(3D)network structure through PAN carbonization,yielding MXene/C aerogels.The 3D network effectively extends the path of microcurrent transmission,leading to enhanced conductive loss of electromagnetic(EM)waves.Moreover,the aerogel’s rich pore structure significantly improves the impedance matching while effectively reducing the density of the MXenebased absorbers.EM parameter analysis shows that the MXene/C aerogels exhibit a minimum reflection loss(RL_(min))value of−53.02 dB(f=4.44 GHz,t=3.8 mm),and an effective absorption bandwidth(EAB)of 5.3 GHz(t=2.4 mm,7.44–12.72 GHz).Radar cross-sectional(RCS)simulations were employed to assess the radar stealth effect of the aerogels,revealing that the maximum RCS reduction value of the perfect electric conductor covered by the MXene/C aerogel reaches 12.02 dB m^(2).In addition to the MA performance,the MXene/C aerogel also demonstrates good thermal insulation performance,and a 5-mm-thick aerogel can generate a temperature gradient of over 30℃ at 82℃.This study provides a feasible design approach for creating lightweight,efficient,and multifunctional MXene-based MA materials.

Defect engineering in N-doped OMC for lightweight and high-efficiency electromagnetic wave absorption

Developing low density and efficient dielectric loss materials has become a research hotspot,which can greatly meet the demands of modern radars and settle the problem of electromagnetic wave pollution.Herein,a series of N-doped ordered mesoporous carbon(OMC)materials with different nitrogen content were prepared via a modified self-assembly method and defect engineering in subsequent calcination treatment.It was discovered that the content and type of nitrogen doping can be effectively modulated by the amount of precursor dicyandiamide,resulting in the changes in porous structure,carbon defects,electromagnetic properties,microwave absorption(MA)performance and radar cross section(RCS)reduction values.Remarkably,as-fabricated OMC/N2.5 displays ideal MA performance,whose minimum reflection loss(RL(min))value reaches−35.3 dB at 7.76 GHz(3.0 mm)and its effective absorption bandwidth reaches 3.52 GHz(10.64-14.16 GHz,2.0 mm).Furthermore,the optimal RCS reduction values can be obtained as 12.01 dB·m^(2) when the detection theta is 30°,which validly reduces the chances of being detected by radar.Thus,this work opens up a novel way for the development of lightweight and high-efficiency MA materials.

Synthesis of covalently bonded reduced graphene oxide-Fe_(3)O_(4) nanocomposites for efficient electromagnetic wave absorption

High-performance electromagnetic(EM)wave absorbers,covalently bonded reduced graphene oxideFe_(3)O_(4) nanocomposites(rGO-Fe_(3)O_(4)),are synthesized via hydrothermal reaction,amidation reaction and reduction process.The microstructure,surface element composition and morphology of rGO-Fe_(3)O_(4) nanocomposites are characterized and corresponding EM wave absorption properties are analyzed in great detail.It demonstrates that Fe_(3)O_(4) nanoparticles are successfully covalently grafted onto graphene by amide bonds.When the mass ratio of rGO and Fe_(3)O_(4) is 2:1(sample S2),the absorber exhibits the excellent EM wave absorption performance that the maximum reflection loss(RL)reaches up to-48.6 dB at 14.4 GHz,while the effective absorption bandwidth(RL<-10 dB)is 6.32 GHz(11.68-18.0 GHz)with a matching thickness of 2.1 mm.Furthermore,radar cross section(RCS)simulation calculation is also adopted to evaluate the ability of absorbers to scatter EM waves,which proves again that the absorption performance of absorber S2 is optimal.The outstanding EM wave absorption performance is attributed to the synergistic effect between dielectric and magnetic loss,good attenuation ability and excellent impedance matching.Moreover,covalent bonds considered to be carrier channels can facilitate electron migration,adjust EM parameters and then enhance EM wave absorption perfo rmance.This work provides a possible method for preparing efficient EM wave absorbers.