Study On The Absorbing Characteristics And Mechanism Of Nickel Single Atom Doped Graphene Aerogel Composites

With the advent of the electronic information age,the development of wireless communication technology and electronic equipment has been very mature,which brings convenience to human life and also causes electromagnetic radiation pollution.Excessive electromagnetic radiation is harmful to human health,and also affects the operation and service life of precision electronic equipment.Therefore,the development of high-performance electromagnetic wave（EMW）absorption materials with absorption wave bandwidth,strong absorption capacity,thin matching thickness and low density has become a research hotspot in today’s society.Two-dimensional（2D）graphene as a novel of carbon material has low density,large specific surface area and high charge carrier mobility shows its application potential in electromagnetic wave absorption.Since the surface of graphene contains a large number of oxygen-containing functional groups,it has a certain degree of dispersibility in aqueous solution.Thus,the special three-dimensional（3D）graphene aerogel structure can be constructed by simple hydrothermal self-assembly process to improve the EMW absorption performance.At the same time,the porous network structure of the aerogel provides a larger internal free space,which increases the multiple scattering of electromagnetic waves inside the material.Recently,Metal single-atoms（M-SAs）have attracted widespread attention in the electrocatalysis due to their ultrahigh surface free energy,high atomic dispersion and high atomic utilization efficiency.However,there are few reports on the preparation of lightweight and high-efficiency EMW absorbing materials by anchoring metal single atoms on graphene aerogel sheets.Therefore,three-dimensional graphene aerogels doped with different contents of nickel single atoms composite absorbing material and its control groups are prepared,and their EMW absorption properties and mechanisms are discussed.In this paper,the different contents of nickel single atom/nitrogen-doped graphene aerogel（Ni-SA@NRGA）composites were successfully prepared by hydrothermal method and annealing heat treatment.And the morphology and structure of the prepared materials were characterized by SEM,TEM,XRD,XPS,Raman and other means.The results show that Ni-SA@NRGA obtained by acid etching retains the same intact sheet-like morphology structure as nitrogen-doped graphene aerogel（NRGA）.In addition,micropores can be observed in the graphene sheet,which is conducive to the anchoring of nickel metal single atoms（Ni-SAs）.In particular,the M-SAs coordinated with nitrogen species（M-N_x）anchored on the carbon matrix had good stability.Electrons around M-N_xmoieties would redistribute due to the different electronegativity of the metal,nitrogen and carbon atoms.The electronic interactions among the different atoms and the redistribution of the charge changed the electrical conductivity and created local polarization system,which could promote the EMW absorption property of the carbonaceous materials containing M-N_xmoieties.The electromagnetic parameters and reflection loss of the prepared samples were measured.The high absorption performance is the Ni-SA@NRGA prepared by doping nickel chloride hexahydrate（NiCl₂·6H₂O）content of 0.7 g,which has the minimum reflection loss of-49.46 dB at a thickness of only 2.0 mm.Furthermore,when the matching thickness is only1.5 mm,the widest effective absorption bandwidth（EAB）can reach 3.12 GHz.At the same time,even if the matching thickness is in the range of 1.2～2.0 mm,the minimum reflection loss of Ni-SA@NRGA can reach below-20 dB,while the mass ratio of the absorbing material to paraffin is only 25 wt%.In contrast,when the matching thickness is 2.5 mm,the Ni-SA@NRGA prepared with the doped NiCl₂·6H₂O content of 0.35 g and 1.40 g has the minimum reflection loss values of-35.70 dB and-41.67 dB respectively.The EMW absorbing properties of these two samples are worse.In summary,Ni-SA@NRGA synthesized by a simple hydrothermal method in this paper,which has the characteristics of light weight,strong wave absorbing ability,thin matching thickness and absorption wave bandwidth.It has great application prospects in the field of electromagnetic wave absorption,and it also provides new methods and ideas for preparing new lightweight electromagnetic wave absorption materials.