Preparation Of Light Graphene-based Composites For Microwave Absorption And Electromagnetic Interference Shielding

With the development of information technology and the popularization of electronic devices,electromagnetic pollution has gradually attracted more and more attention.The fabrication of electromagnetic shielding and absorbing materials with excellent performance are in great demand.At present,people are no longer satisfied with the traditional electromagnetic shielding and absorbing materials and they need to satisfy more requirements.The materials are not only expected to have a good quality of electromagnetic shielding and absorbing wave,but also have the advantages of light weight,thin thickness,environment friendliness tolerance and excellent mechanical properties,et al.One-layer graphene was exfoliated from natural graphite in 2004 and then more and more researches have been focused on the graphene fields.Graphene has excellent electrical and thermal conductivity,high Young's modulus and good light transmittance,and is widely used in electromagnetic shielding,wave absorption,energy storage and photovoltaics.Graphene has a theoretical surface area as high as 2600 m2·g-1 and graphene-based composite material can achieve light weight and small density while ensuring excellent performance.But the stacking and agglomerations of large numbers of graphene materials during processing may result in the loss of large surface area and affect the performance of graphene materials.Self-assembling graphene into three-dimensional structure is a good way to avoid the agglomeration between graphene sheets and improve the properties of the material.Typical three-dimensional graphene materials include graphene foams,graphene sponges,graphene aerogels,etc.They can be used to prepare light-weight wave-absorbing materials by ensuring materials with excellent properties and lower filling capacity.The two-dimensional graphene film also has a very thin and light characteristic,and it can better highlight the advantages of the single-layer graphene compared to other graphene materials.At the same time,the graphene film has high conductivity,low density and good flexibility,bending and folding properties,and is an ideal choice for preparing a flexible and light-weight electromagnetic shielding material.In order to meet the new requirements for electromagnetic shielding and absorbing materials,it is very important to prepare light-weight materials with excellent environmental resistance and mechanical properties.In this work,light graphene-based electromagnetic shielding and absorbing materials with high conductivity have been prepared and they have good environmental resistance,along with light and flexible properties.The specific research contents are as follows:1.Graphite oxide(GO)prepared by modified Hummers method is used as the precursor to mix with SiC nanofibers for the composites.SiC nanofiber-loaded GO is self-assembled into three-dimensional graphene/SiC hydrogel under the reduction of Vitamin C and then the hydrogel is freeze-dried to get graphene/SiC aerogel.This light weight and porous material can effectively maintain the high specific surface area.Making full advantage of the single-layer graphene,the prepared composite aerogel can improve the multiple reflection of electromagnetic waves and increase the interfacial polarization of the material,which can be an ideal material for the electromagnetic shielding applications.2.Anneal the three-dimensional graphene/SiC aerogel at different temperatures.Changing the temperature can adjust the electrical conductivity and the dielectric constant of the material,which makes the material achieve a good impedance match and improve the microwave absorption properties.The minimum value of reflection loss at 15.6 GHz for the composite with a thickness of 1.15 mm can reach-38.5 dB.The minimum reflection loss(RL)at 16.8 GHz with a thickness of 0.45 mm can reach-31.3 dB,indicating that the material can achieve good microwave absorption performance at low thickness.3.Cellulose nanocrystals(CNC)is prepared by sulfuric acid hydrolysis of microcrystalline cellulose.The CNC and GO are composited by suction filtration and then reduced by HI to form a graphene/CNC thin film.By adding CNC,the mechanical properties of the film are improved,and the graphene/CNC film becomes a flexible film with excellent mechanical properties,light weight,thin thickness,and good electromagnetic shielding performance.When the thickness of the film is 6 ?m,the electromagnetic shielding performance can reach?13 dB,and the electromagnetic shielding performance can reach a decibel of 2167 dB·mm-1.The mechanical properties of the material are adjusted by changing the concentration of the CNC in the film,and the film can show better mechanical properties and flexibility.When the content of CNC is 5%,the mechanical properties of the film can reach 76.0 MPa.