Doping And Interfacial Regulation Of Carbon Nanotubes And Their Electromagnetic Wave Absorption Performance

Traditional electromagnetic wave（EMW）absorption materials,such as ceramics,ferrites,and metal magnets,are difficult to meet the requirements of lightweight and ultrathin under the premise of strong EMW absorption properties due to the influence of height density.To solve this problem,ultralight carbon nanotubes（CNTs）with high anisotropy,excellent stability,high conductivity,and large aspect ratio have attracted extensive attention as EMW absorption materials.However,CNTs have low EMW absorption properties due to the lack of polarization center and poor impedance matching.For this reason,many researchers have done a lot of work to improve the EMW absorbing performance of CNTs-based materials.However,on the basis of satisfying the wide effective absorption bandwidth（EAB）and strong reflection loss（RL）,it is still an important problem to minimize the filling ratio and thickness of CNTs-based absorption materials.Therefore,from the aspects of enhancing dipole polarization,interface polarization and conductance loss,a series of CNTs-based materials have been designed and prepared by doping and interface regulation strategies in this paper,and their EMW absorption properties and loss mechanism have been studied in the2-18 GHz band.The main research contents of this paper can be summarized as follows:In situ catalytic strategy was proposed for the preparation of hierarchical nitrogen-doped carbon skeletons/nitrogen-doped carbon nanotube arrays containing encapsulated metal（M=Fe,Co,and Ni）nanoparticles（HMCNTs）with the assistance of dicyandiamide using metal-NTA complex nanowires as precursors.The EMW attenuation properties of HMNCNTs embedded with different metal nanoparticles were investigated,while the effect of hierarchical 3D structure on EMW performance was also discussed.Experimental results indicated that the reason for the excellent EMW absorption performance of HMCNTs was that the HMCNTs prepared by in situ catalysis have abundant homogeneous/heterogeneous interfaces and enriched dipoles generated by structural defects and heteroatomic doping,which were conducive to enhancing relaxation loss.In addition,the 3D interconnected conductive network and large specific surface area of the hierarchically structured HMCNTs help to improve the conductivity loss of the material and reduce the filling ratio of the absorber.Mn,N co-doped carbon nanotubes（Mn-N_x/NCNT）were prepared by polymerization,carbonization and acid etching methods using MnO₂ as a template.The introduction of atomically dispersed Mn-N_x moieties enhanced the polarization loss of CNTs while retaining ultra-light properties.The Mn-N_x/NCNT exhibits excellent EMW absorption performance at a filling ratio of only 7 wt%.Experimental and density functional theory calculation results indicated that the electronic structure and polarizability of the NCNTs were adjusted by the atomically dispersed Mn-N_x,leading to the increase in conduction and polarization losses of Mn-N_x/NCNT,and thus in the EMW property.Co Mn-MOF was grown uniformly on MnO₂ nanowires by wet chemical synthesis using ultra-long MnO₂ nanowires as template.Hierarchically pearl necklace-like nanostructures Co Mn@CN was prepared by carbonization.This strategy effectively prevented agglomeration during Co Mn-MOF growth and carbonization,and constructed Mn₃Co₇ alloy and abundant heterogeneous interfaces.Experimental and theory calculations demonstrated that the enhanced EMW absorption property was attributed to the high conductivity and rich interfacial polarization caused by the pearl necklace-like structure,and dielectric relaxation loss caused by the electron interaction between Co and Mn atoms in Mn₃Co₇ alloy.Therefore,Co Mn@CN exhibited a broad EAB（5.24 GHz）with the matching thickness of only 2.0 mm.Based on cheap and renewable chitosan and multi-loss modes 3D hierarchical structure HMCNTs,HFe Ni CNT/NCA aerogel was designed and prepared by freeze-casting and pyrolysis.HFe Ni CNT/NCA not only inherited the advantages of HMCNTs,but also the unique layered structure maximizes improved the reflection and scattering times of EMW in free space,thus enhancing the energy consumption of EMW.