Synthesis of Porous 3D Fe/C Composites from Waste Wood with Tunable and Excellent Electromagnetic Wave Absorption Performance

Here, we synthesized Fe/C composites with different crystal structures (Fe 3 O 4 @C, Fe 3 O 4 /Fe@C, or Fe 3 C@C) by carbonizing iron(III) 2,4-pentanedionate (Fe(acac) 3 ) pre-enriched forestry waste wood at different pyrolysis temperatures from 400 to 1000 °C. The obtained samples are porous 3D (three-dimensional) biochars inlaid with varied Fe phases. The corresponding EMW absorbing properties are proved to be dependent on the pyrolysis temperature, as well as the resulting crystal structures and graphitization degrees. Among them, Fe 3 C@C obtained at 1000 °C possesses excellent EMW absorbing properties with a minimum RL value of −57.64 dB at 6.92 GHz and a wide response bandwidth of 5.00 GHz covering 6.36–11.36 GHz. This good performance is due to continuous substances of Fe 3 C covering the inner surface of the conductive biochars, permitting the optimal impedance matching along with the strongest dielectric loss and optimal magnetic loss. Moreover, more defects are generated at 1000 °C which act as the dipole center and produce dipole relaxation polarization. The dipole relaxation is proved to be positive for improving the EMW absorbing performance together with the interface polarization between C–Fe 3 C.