Preparation And Electromagnetic Properties Of Carbon Materials Doped With Heterogeneous Elements

5G technology has brought opportunities and conveniences to the global economy and social life.However,the increasing of electromagnetic interference is depleting these advantages.Therefore,it is necessary to investigate high efficiency electromagnetic wave absorbing materials to solve the problem of electromagnetic wave radiation.As is known,carbon nanomaterials have been increasingly used and regarded as ideal EM wave absorbers because of its relative low density,adjustable performance and various forms.Various nanostructured carbon materials such as carbon nanofibers(CNFs),carbon nanotubes(CNTs),carbon nanosheets(CNSs)and graphene,are advantageous as hosts for fantastic dielectric properties owing to its excellent conductivity and charge carrier mobility.Despite many carbon nanomaterial absorbers having been made,it remains a big challenge to control the impedance matching due to the large distinction between complex permeability and complex permittivity,which blocks its practical use in the domain of electromagnetic(EM)wave absorption.Using magnetic metals(Fe,Co,Ni),metal oxides(NiO,ZrO2)and ferrites(ZnO·Fe2O3,Ni-Zn·Fe2O4)to build carbon nanomaterial matrix composites is an important way to improve its characteristic impedance matching and EM wave absorption property.Unfortunately,it must be pointed out that the enhancement of EM wave absorption is at the cost of low density and corrosion resistance of carbon nanomaterials due to the insert of metal-based secondary components,which limits their applications in durable performance.Therefore,it is of great significance to try to replace metal based secondary components,especially to study the structure-activity relationship,in order to improve the durability and electromagnetic absorption performance of composites.Recently,metal-organic frameworks(MOFs)are promising hybrid functional materials due to their readily tunable structure and exceptionally high thermal stability.In the process of pyrolysis,a large number of MOFs with high thermal stability have become nitrogen doped carbon nanomaterials.Because of its special structure-activity relationship,EM wave absorbing materials with atom dispersed metal sites have become a new research hotspot.Materials with atom dispersed metal sites can effectively solve the problems caused by the composite of secondary components.Metal-nitrogen-carbon materials(MN-C,M is a nonprecious metal)have unique structures and high atom utilization efficiency.In addition,the pyrolysis of compounds@MOFs hybrid materials is also an effective method to prepare M-N-C composites.Biomass materials such as cotton,plant leaves,peanut shell and wheat straw have been attracting considerable attention because of rich reserves,renewable,low cost,light weight and non-toxicity.Cotton is one of the mostly common biomass materials with functional groups and it is emphasized that it naturally contains multiple doping elements,such as C,O,S,P,N.The pyrolysis process leads to the formation of hollow structure of the carbon fiber,which means that the resulting fiber has ultralight density.In this study,we used MOFs and cotton as the precursors to study the EM wave absorption characteristics.It is found that the dielectric loss of carbon materials can be effectively adjusted by separating the charge of local microstructure and inducing a considerable electric dipole polarization without the introduction of secondary elements.