Walnut shell-derived nanoporous carbon@Fe3O4 composites for outstanding microwave absorption performance

Porous carbon has been considered to be a promising light and high-efficient microwave absorber, but the nonmagnetic and relatively poor impendence matching property have limited its advanced applications. Herein, the nanoporous biomass carbon (NBC) was prepared by using the ZnCl2 to activate the walnut shells. The NBC showed excellent microwave absorption (MA) performance, whose minimum reflection loss (RL) value reached -36.9 dB at 8.2 GHz. What's more, for the purpose of improving the impedance matching, Fe3O4 nanoparticles were generated on the surface of NBC by in situ synthesis. The minimum RL value of as-prepared NBC@Fe3O4 composites could reach -40.3 dB at 17.5 GHz with a thin thickness of 2.0 mm and the effective absorption bandwidth (RL <= -10 dB) was 6.6 GHz when the thickness was 2.5 mm. Compared with NBC, the promoted MA performance of NBC@Fe3O4 composites was due to the improved impedance matching and synergistic effect between dielectric loss and magnetic loss. We believe that as-prepared NBC@Fe3O4 composites have a great potential as an efficient microwave absorber. (C) 2019 Elsevier B.V. All rights reserved.