Organic acid etching strategy for synthesis of ZIF-8@ZIF-67-Derived hollow Co@C/C rods with excellent electromagnetic wave absorption in C-band

The development of metal–organic frameworks (MOFs)-derived magnetic carbon-based materials for high-efficiency electromagnetic wave (EMW) absorption has attracted widespread attention. While these MOFs-derived composites have shown exceptional performance in absorbing EMWs within the X and Ku bands, the pursuit of effective absorption at lower frequencies remains a challenge. Herein, we demonstrate a novel strategy to synthesize hollow Co@C/C rods with excellent C-band EMW absorption via acetic acid etching and pyrolysis of core–shell ZIF-8@ZIF-67. Based on acetic acid etching, ligand-deficient ZIF-8@ZIF-67 rods with abundant mesoporous structures are constructed, enabling precise control over the Co nanoparticles content, graphitization degree, and pyridinic N doping in the derived Co@C/C. This simple fine-tuning approach simultaneously reduces dipole polarization by lowering the pyridinic N doping concentration, suppresses interfacial polarization and conduction loss through reducing the number of graphitic carbon layer, and enhances magnetic loss by increasing the Co content. These combined effects collectively improve the impedance matching of Co@C/C for low-frequency absorption. Notably, as the volume of acetic acid solution increases, the absorption frequency band of Co@C/C gradually shifts from the Ku-band to the C-band, while sustaining superior EMW absorption performance. At the filling ratio of merely 11 %, the RL min values for Co@C/C-20 and Co@C/C-30 achieve −49.8 dB and −34.7 dB at 7.2 GHz and 6.8 GHz, respectively. This study offers a valuable approach to the development of lightweight materials with excellent EMW absorption in C-band.