Research On The Microwave Absorption Performance Of Enhanced Graphene Aeroge

Electronic information technology brings convenience to human life and national defense security at the same time,but also accompanied by electromagnetic interference,electromagnetic radiation,information leakage and a series of security issues.So far,a lot of work has been done in developing"thin,light,wide and strong"electromagnetic wave absorbing materials to eliminate electromagnetic hazard.Three-dimensional（3D）network structures have been believed to extend the reflection/scattering path of incident waves and improved the absorbing properties of materials.Commonly used three-dimensional templates such as lightweight foam and alumina are complicated to produce and have no wave-absorbing properties of their own.If the template is replaced by a wave-absorbing material,the wave-absorbing properties of the composite material will be further enhanced.Therefore,it is crucial to design 3D wave-absorbing skeleton structures with processability and structural stability.Graphene oxide（GO）has attracted much attention because of its many unique properties such as light weight,large specific surface area and processability,and its self-assembled 3D structure（Graphene oxide aerogel,GOA）can be used as a 3D template for wave absorbing materials,but the GOA structure is unstable and prone to collapse and weak wave absorption loss capability,which is challenging to improve.Therefore,this thesis firstly improved the structural strength of GOA to improve its wave absorption performance while maintaining structural stability,as follows:（1）In order to enhance the mechanical strength of aerogels,GO/FCNTs/epoxy composite aerogels（GCEA）with 3D structure were prepared by hydrothermal and freeze-drying methods using functionalized carbon nanotubes（FCNTs）and epoxy resin as reinforcement materials.The effects of different ratios of GO/FCNTs and epoxy resin on the mechanical strength and wave absorption properties of the aerogels were investigated,and the optimal ratio was found.The results showed that GCEA-2 had excellent structural stability,thermal stability and mechanical strength,which can be attributed to theπ-πcovalent cross-linking of carbon nanotubes and the synergistic enhancement of epoxy resin-CONH-chemical cross-linking.Due to the dielectric loss of FCNTs and the interconnected three-dimensional structure,the RL_min of GCEA-2 was-35.6 d B and the EAB_max was 2.64GHz at a thickness of 9.9 mm.（2）To improve the wave absorption performance of aerogels,reduced graphene oxide composite aerogels（RGCEA）were prepared by in situ chemical reduction of GCEA,and the wave absorption performance and absorption mechanism of aerogels under different reduction times were investigated.The results showed that the in situ chemical reduction method did not destroy the cross-linked structure of GCEA.Due to the enhanced dielectric loss,the absorbing performance of RGCEA was significantly improved compared to that of GCEA.The RL_min of RGCEA-6 reached-48.04 d B when the filling amount was 5 wt%and the reduction time was 6 h,corresponding to a thickness of 2.5 mm;when the thickness was 2.2 mm,the EAB_max was 5.76 GHz.The longer the reduction time,the better the absorption performance obtained at low filling rate,so the electromagnetic wave absorption performance of RGCEA can be tuned by adjusting the filling rate and reduction time.（3）To further regulate impedance matching and improve electromagnetic wave absorption,r GCEA@Fe₃O₄ composite absorbing materials with both dielectric and magnetic loss capabilities were prepared by in-situ chemical co-precipitation,and their absorption mechanism and the effect of iron ion concentration on electromagnetic wave absorption performance were investigated.It was found that the Fe₃O₄ nanoparticle content increased and the electromagnetic wave absorption performance of the graphene composite aerogel enhanced and then weakened with increasing concentration.Due to the unique"chemical plating structure"and the reduction of GCEA by Fe²⁺as a green reducing agent to form a three-dimensional conductive pathway,the wave absorption performance of r GCEA@Fe₃O₄ was significantly improved compared to that of GCEA.r GCEA@Fe₃O₄-3had the best electromagnetic wave absorption performance at a fill rate of 10 wt%.At 12.08GHz and 2.5 mm thickness,the minimum RL value reached-58.13 d B,and the maximum effective bandwidth was 6.64 GHz when the thickness was 2.2 mm.The deposition of high-strength hydrophilic three-dimensional graphene composite aerogels as templates for wave-absorbing materials is expected to develop into multilayer three-dimensional wave-absorbing matrices for the preparation of structural-functional composites.