Research On Electromagnetic Wave Absorption Properties And Preparation For Transition Metal Loaded Carbon Aerogels

The rapid development of electronic information technology has brought about an efficient and convenient life,the electromagnetic radiation generated by mobile electronic devices has become increasingly serious,and electromagnetic pollution has become a new source of pollution that threatens health.The electromagnetic wave absorbing materials have the problems of high density,low properties and high filling ratio.Carbon aerogels are widely used in the fields of sensors,electrochemistry,and energy storage due to their high porosity,low density,excellent electrical conductivity,and good mechanical strength.At present,some researchers have studied the electromagnetic wave absorption properties of carbon aerogel composites,which show certain application prospects,but there are problems such as low performance and imperfect absorption mechanism.In this thesis,a series of transition metal-loaded carbon aerogel electromagnetic wave absorbing materials were controllably prepared by sol-gel method,directional freeze-drying method,secondary ion adsorption and defect anchoring strategy.The microstructure,morphology,and composition of transition metal-loaded carbon aerogel can be adjusted to optimize the electromagnetic parameters,so as to achieve excellent electromagnetic wave absorption properties.At the same time,the electromagnetic wave absorption mechanism of transition metal-loaded carbon aerogels is deeply studied.The main content as follows:Through the sol-gel method and high-temperature annealing treatment,the ultralight self-supported graphene aerogel containing carbon nanotubes and magnetic nanoparticles was designed and constructed.The effects of synthesis conditions on the morphology,composition and electromagnetic wave absorption properties of aerogel were investigated.The minimal reflection loss of aerogels reaches-43.84 d B and the maximum effective absorption bandwidth is up to 4.24 GHz when the filling ratio is only 8 wt.%.The electromagnetic energy conversion efficiency of aerogels is 24.56%.Considering the application of electromagnetic wave absorbing materials in harsh environments,the ordered graphene aerogels loaded with cobalt nanoparticles were prepared by directional freeze-casting and carbonization methods.The aerogel has multifunctional properties,such as strong mechanical properties,good thermal insulation properties,excellent thermal management properties,and excellent electromagnetic wave absorption properties.The ordered graphene aerogels prepared by this method have broad application prospects in the fields of aerospace,artificial intelligence and wearable devices.In order to further reduce the density of aerogels,the graphene aerogels with ultra-light cobalt single atoms were prepared by a secondary ion adsorption and defect-anchoring strategy.The secondary ion adsorption can effectively adjust the concentration of cobalt single atoms.When the filling ratio is only 5 wt.%,the minimal reflection loss reaches-49.13d B and the maximum effective absorption bandwidth is up to 4.24 GHz.The excellent electromagnetic wave absorption performance is achieved.Based on density functional theory calculations and Havriliak–Negami equation simulation,the effects of single-atom and single-atom defect structures on electromagnetic wave absorption properties were studied,and the structure-activity relationship between single-atom microstructure and dielectric behavior was elucidated.Based on the structure-activity relationship between single-atom microstructure and dielectric behavior,N/O dual-coordinated cobalt single-atom carbon nanofiber aerogel（Co-N₄-O/NCFF）was prepared using environmentally friendly bacterial cellulose as a substrate.Compared with the Co-N₄ configuration,the Co-N₄-O configuration improves the polarization loss capability.When the filling ratio is low and the thickness is thin,Co-N₄-O/NCFF still shows excellent electromagnetic wave absorption properties.The minimal reflection loss is up to-41.32 d B and the effective absorption bandwidth is 4.02 GHz.In this thesis,several transition metal-loaded carbon aerogels have been controllably prepared,all of which have excellent electromagnetic wave absorption properties.Meanwhile,their electromagnetic wave absorption mechanisms were analyzed based on structural characterization,electromagnetic parameters,density functional theory calculations and Havriliak–Negami equation simulation.In addition,their electromagnetic wave attenuation ability was simulated by microwave simulation software.The transition metal-loaded carbon aerogel materials designed in this thesis have certain potential in practical applications.