| Electromagnetic interference(EMI)shielding and microwave absorbing(MA)materials are used to avoid the harmful effects on communication systems,sensitive electronic equipment,and living organisms.Carbon based materials,including carbon black,carbon fiber,graphene and carbon nanotube,show merits of low density,high electrical conductivity and high flexibility.Therefore,carbon materials are widely exploited as EMI shielding and MA materials.Here,in order to improve the EMI shielding and MA performances of carbon based materials,we designed series of porous carbon materials with high EMI shielding or MA properties.The main work in the article includes the following four parts:1.Graphene aerogel films(GAF)with multilayer structure were fabricated through free expansion of reduced graphene oxide(rGO)films.The experimental results signify that expansion in a multilayer structure can significantly increase the EMI shielding performance of a material,and we denote this phenonmon as expansion enhancement effect(EEE).The mechanism of EEE was explored in detail based on electromagnetic theories.The GAFs with high electrical conductivity and EEE demonstrate high EMI shielding performance,reaching?135 dB in 0.1-3 GHz at thickness of 1.4 mm.The thickness-averaged specific shielding effectiveness(TASSE)reaches 100,000 dB cm2 g-1,which is among the best in open literatures.2.Porous biomass-pyrolyzed carbons(PBPC)were fabricated by a two-step method including gum removing and pyrolyzation.By controlling the reduction temperature(660,670,680,690,700,720 0C),PBPCs show different electrical conductivity and MA performances.The PBPCs pyrolyzed at 680(PBPC-680)or 690?(PBPC-690)demonstrate the best MA performance.PBPC-680 shows peak intensity of-68.3 dB at thickness of 4.28 mm,and the effective absorption bandwidth(EAB)reaches 6.1 GHz(8.2-14.3 GHz).The EAB reaches its optimum for PBPC-690,reaching 7.6 GHz(9.8-17.4 GHz)at thickness of 3.73 mm.3.Graphene aerogels(GA)with flat structural units and different graphene load were fabricated through two steps of free-drying and chemical reduction.The experimental results show that GA-1 with original graphene oxide concentration of 1 mg ml-1 performs the best in MA.The peak intensity reaches-26.1 dB at thickness of 3 mm,and the EAB reaches 7.2 GHz(8.1-15.3 GHz)at thickness of 4 mm.Remarkably,the density of GA-1 is only 0.68 mg cm-3,which is far lower than the MA materials in open literatures.4.Bi-continuous composite foams(BCCF)with two independent networks:graphene framework and melamine skeleton were fabricated through two steps of methods including immersing assembly and chemical reduction.The experimental results demonstrate that BCCFs with edge-supporting structure can fulfill high MA performance at low graphene filler content.The BCCF with graphene filler content of 3.40 mg cm-3 fulfills peak intensity of-34.8 dB and the EAB reaches 9.0 GHz(9.0-18 GHz),which are among the best in open literatures.Besides,the BCCFs with bi-continuous structure demonstrate series of other advantages,such a high tensile strength(?80 KPa),high breakage elongation(>22.2%),high elasticity,extremely low percolation threshold(0.006 vol%)and oil-adsorption properties(>60 times of their own weight).Therefore,BCCFs are low-cost,highly efficient and high-performance multifunctional materials.In summary,in order to fabricate materials with high EMI shielding performance or MA performance,we designed carbon-based materials with different microstructures,including porous biomass pyrolyzed carbon,graphene aerogel films,graphene aerogels and bi-continuous composite foams.The EMI shielding performance or MA performance of materials with different microstructures were systematically investigated.The principle in maximizing the EMI shielding or MA performances through structural design and conductivity optimization was proposed.we believe that this work would be highly valuable for future research on EMI shielding materials and MA materials. |
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