Covalent organic framework-derived hollow core-shell Fe/Fe3O4@porous carbon composites with corrosion resistance for lightweight and efficient microwave absorption

Abstract The functionalization of covalent organic frameworks (COFs) has recently captured great attention due to their designable structures and high specific surface area. However, their application in the field of microwave absorption is still scarce. In this work, hollow core-shell Fe/Fe3O4@porous carbon composites were successfully synthesized by calcining Fe3O4@COF composites. The composite obtained after heat treatment inherits the characteristics of porous and high specific surface area of the COF material, and the hollow core-shell porous structure facilitates multiple reflections and scattering of electromagnetic waves, the increase of active center sites, and the improvement of impedance matching. The results demonstrate that the composite exhibits efficient electromagnetic absorption performance at ultra-thin matching thickness (d = 1.8 mm): the minimum RL value is -50.05 dB and the effective absorption bandwidth is 5.20 GHz. Meanwhile, the absorption band with RL