Customizing defect location in MWCNTs/Fe3O4 composites by direct fluorination for enhancing microwave absorption performance

Constructing magnetic-dielectric composites is an effective approach to prepare high-performance multi-walled carbon nanotubes (MWCNTs)-based microwave absorbers. The current composite design strategies mainly focus on the regulation of magnetic materials, while the effect of MWCNTs structure on the microwave absorption (MA) performance is still unclear. Herein, F-MWCNTs with different fluorinated depths, namely surface fluori-nation (S-F-MWCNTs) and deep fluorination (D-F-MWCNTs) were prepared by molecular-fluorination and atomic-fluorination, respectively. The fluorine atoms on F-MWCNTs were defluorinated in the next loading process, achieving customization of defect location in MWCNTs/Fe3O4 composites. In relation to the fluorination depth of F-MWCNTs, the defects of S-F-MWCNTs/Fe3O4 were mainly distributed on the outer tube of MWCNTs, while they were on both inner and outer tubes of MWCNTs for D-F-MWCNTs/Fe3O4. Under the electromagnetic field, the inner tube defects of D-F-MWCNTs/Fe3O4 were excited to produce enhanced polarization loss and conductive loss. As a result, compared with S-F-MWCNTs/Fe3O4 with only outer tube defects, D-F-MWCNTs/ Fe3O4 with both inner and outer tube defects exhibited better MA performance. Further regulating the fluorine content of D-F-MWCNTs, we can adjust the optimal absorption band shifting from high frequency to low fre-quency. Our work illustrates the importance of inner tube modification of MWCNTs to prepare high-performance MWCNTs-based microwave absorbers.