Study On The Enhancement Of Microwave Absorption Performance By Defect-induced Polarization Loss In Carbon-based Composite

Electromagnetic wave absorbing materials are playing an increasingly important role in modern society due to their applications in the military and 5G intelligent era.Defect engineering is an effective way to manipulate electromagnetic parameters and improve electromagnetic absorption capacity.Carbon-based materials are widely used in electromagnetic wave absorption materials because of their simple synthesis process,low density,and good conductivity.Therefore,based on graphene and carbon-based metal-organic skeleton（MOFs）,precisely defect design was adopted to explore the influence of defect-induced polarization loss on electromagnetic wave absorption performance.The research of this thesis has important significance and practical demand for the development of electromagnetic wave absorption field.As a traditional dielectric loss material,graphene has been used in the field of electromagnetic wave absorption.However,the improvement of dielectric loss is limited for pure graphene,impeding its widely application.Chemical doping of graphene with heteroatoms is considered a promising strategy for enhancing the absorption of electromagnetic waves.We prepared single-atom dispersed Fe/N-doped graphene oxide（Fe Pc/N-GO）composites by annealing method.It is found that Fe Pc/N-GO composites have excellent electromagnetic wave absorption performance for the following reasons:i)The decrease conductivity of graphene improves the impedance matching of the composites;ii)The presence of Fe-N,pyrrole/pyridine N is essential to the contribution of polarization relaxation loss,while graphite N is conducive to conduction loss;iii)Density functional theory（DFT）calculation results show that change of the charge density in Fe Pc/N-r GO contributes to the generation of permanent electric dipoles,thus enhancing the absorption performance of electromagnetic wave.When the thickness of the absorber of Fe Pc/N-GO composite is 3.8 mm,the minimum reflection loss(RL_min)can reach-49.3 d B at the frequency of 5.44 GHz,the effective absorption bandwidth（RL≤-10 d B,EBA）is 3.2 GHz,and the filling capacity is only5%.The results show that the defects induced by Fe and N doping can effectively improve the polarization loss and electromagnetic wave absorption performance.In addition,MOFs formed by the combination of metal and organic ligand have high specific surface area and effective porosity.Porous carbon-based precursor materials for electromagnetic wave absorption can be obtained by in situ hot carbonization process.Two-dimensional Zn O is a dielectric loss material,which can be used in carbon-based porous composites to improve the conductivity and impedance matching.Therefore,Ni O/Ni/C/Zn O composites derived from Ni-MOF were synthesized by two-step hydrothermal and annealing methods.Compared to Ni/C composites(RL_min=-38.6 d B at 16.72 GHz),the RL_min of Ni O/Ni/C/Zn O composites at 14.92 GHz can reach-61.20 d B,it indicates that the electromagnetic wave absorption performance can be largely enhanced.The excellent electromagnetic wave absorption performance of Ni O/Ni/C/Zn O can be attributed to interface polarization,high specific surface area and porosity,and good impedance matching.