Corncob‐Derived Magnetic Porous Biochar for Broadband and Efficient Microwave Absorption

Agricultural waste‐derived porous biochar has attracted incremental attention in microwave absorption because of its low price, lightweight, good porosity, and conductivity. Herein, corncob is adopted as the carbon source to prepare magnetic Fe ₃ O ₄ /biochar composites via a FeCl ₃ ‐assisted one‐step pyrolysis route. Annealing temperature and FeCl ₃ dosage significantly affect the electromagnetic parameters and the microwave absorption performances of the Fe ₃ O ₄ /biochar composites. Minimal reflection loss (RL _min ) of −49.4 dB and maximal effective absorption bandwidth (EAB) of 6.96 GHz are achieved at annealing temperature of 600 °C and mass ratio of Fe precursor to corncob of 2:1, which are likely due to the optimal impedance and the strong attenuation capability. Good synergy of conductive biochars and magnetic Fe species significantly optimize the impedance matching and distinctly enhance the wave dissipating capacity of the Fe ₃ O ₄ /biochar composite, thereby resulting in broadband and efficient microwave absorption over CC600Fe2.