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.