Hierarchical FeCo@C/N-CNTs heterostructure with 3D conductive network for efficient electromagnetic wave dissipation

Electromagnetic wave absorbing materials (EMWAMs) are increasingly being applied in modern life, and composite materials with hierarchical structures are expected to be an effective means to address the limitations of the performance of a single component. This paper designs and prepares a material with a multi-level structure. Firstly, a bimetallic MOF (MIL-101(FeCo)) is synthesized by the hydrothermal method. Then, using dicyandiamide (DCDA) as the carbon/nitrogen source in the gas, In-situ catalytic growth nitrogen-doped CNTs and FeCo nanoparticles are simultaneously synthesized through thermal decomposition and calcination. Finally, a FeCo@C/N-CNTs composite material with a three-dimensional conductive network and a core-shell heterostructure is obtained. This method effectively overcomes the problem of carbon nanotube agglomeration that often occurs in composite processing. By precisely adjusting the mass ratio of DCDA/MOF and the calcination temperature (700–800 °C), the morphology, graphitization degree and electromagnetic parameters of carbon nanotubes can be optimized, resulting in a sample (FCC-5, precursor ratio 6:1, 750 °C) with excellent absorbing performance (minimum reflection loss (RLmin) of −60.78 dB, effective absorption bandwidth (EAB) of 5.04 GHz. covering 84% of the Ku band with a ultrathin matching thickness of 1.66 mm). This performance is generated by the synergistic action of multiple mechanisms, including the three-dimensional carbon nanotube network enhancing conductive loss, the hetero-interface and N doping enhancing the interface and dipole polarization, and the iron cobalt alloy providing magnetic loss. Radar cross-section (RCS) simulation confirms that at 15.28 GHz, the RCS value is significantly reduced to −16.6 dBm², demonstrating excellent wide-angle radar stealth capability. This work provides a novel example for designing lightweight, broadband and high-strength electromagnetic wave absorbing materials.