Synthesis And Microwave Absorption Properties Of Polyindole Derived Nitrogen-doped Carbon-based Composites

Carbon materials containing nitrogen and other heteroatomic doping can be obtained by carbonization of conducting polymers.The Polyindole derived nitrogen doped carbon based composite material is prepared by combining the Al₂O₃ and Ti O₂/C and has excellent microwave absorption properties.In this work,a series of PINNC-based composites were prepared.XRD,Raman,XPS,SEM,TEM and vector network analyzer were used to characterize the crystal phase structure,graphitization degree,bonding mode of elements,morphology and electromagnetic parameters of the composites.The results are as follows:（1）Polyindole was prepared by in-situ polymerization of indole,and PINNC material was obtained by high temperature pyrolysis of polyindole（PIN）in tube furnace.The effects of pyrolysis temperature on the structure,morphology and microwave absorption properties of PINNC were investigated.The results show that there are multiple regional depressions on the surface of the PINNC sphere.When the electromagnetic wave reaches the surface of the PINNC sphere,most of the incident electromagnetic wave can be absorbed and attenuated due to the fold structure of the carbon sphere.The microwave absorption performance of PINNC was the best when the pyrolysis temperature was 700℃.When the matching thickness is 2.0 mm and the frequency is 15.12 GHz,the minimum reflection loss is-32.85 d B and the maximum effective absorption bandwidth is 6.08 GHz,completely covering the Ku band.（2）Al OOH was prepared by hydrothermal method with KAl（SO₄）₂.12H₂O as raw material and urea as precipitator.Then PIN/Al OOH composite was prepared by in-situ polymerization with Al OOH and indole as raw materials and ammonium persulfate as initiator.PINNC/Al₂O₃ composites were prepared by pyrolysis of PIN/Al OOH composites at 700℃.The effects of mass ratio of Al OOH and indole,material composition and microstructure on microwave absorption performance of PINNC/Al₂O₃composites were investigated.The results show that the PINNC ball is attached to the surface of hemispherical Al₂O₃,which enhances the interface polarization.Due to the unique internal hollow structure of hemispherical alumina,most of the microwaves reaching the surface of hemispherical alumina will be scattered and dissipated.When the mass ratio of Al OOH to indole is 1:4.5,the PINNC/Al₂O₃ composite has the best microwave absorption performance.When the matching thickness is 2.5 mm,the minimum reflection loss of absorbent S2 is-46.08 d B.When the thickness is only 3.0mm,the absorbent S2 has an effective absorption bandwidth of 7.02 GHz.（3）Ti₃C₂Ti_x was prepared by HCl-Li F etching method using Ti₃Al C₂ as raw material,hydrochloric acid and lithium fluoride as etchants,and then PIN/Ti₃C₂Ti_x was prepared by in-situ polymerization using Ti₃C₂Ti_x and indole as raw materials and ammonium persulfate as initiator.PINNC/Ti O₂/C composites were prepared by pyrolysis of PIN/Ti₃C₂Ti_x at 700℃.The effects of mass ratio of Ti₃C₂Ti_x to indole,material structure and morphology on microwave absorption performance of PINNC/Ti O₂/C composites were investigated.The results show that the incident electromagnetic wave will be reflected among the layered carbon nanosheets for many times,which is conducive to microwave attenuation.The structural defects on the nitrogen-doped carbon sphere and carbon layer caused by high temperature pyrolysis and the dipole polarization caused by the doping of in situ nitrogen heteroatoms will further increase the dipole polarization loss.When the mass ratio of Ti₃C₂Ti_x to indole is 1:5.5,the microwave absorption performance of PINNC/Ti O₂/C composite is the best.When the matching thickness reaches 2.5 mm and the frequency is 14.08 GHz,the RL_min reaches-53.42 d B and the EAB reaches 6.24 GHz.Figures[28]Tables[6]References[101]...