FeCo@C composites derived from MIL-101(FeCo) with superior electromagnetic wave absorption ability in the X/Ku bands

Modifying the metal source and microstructure of the metal-organic framework is becoming an effective approach to enhancing the microwave absorption properties of magnetic carbon-based composites. In this work, based on the MIL-101(Fe), we rationally introduced Cobalt ions and used citric acid as a coordinator to regulate grain growth, ultimately leading to the successful synthesis of a spherical bimetallic MIL-10(FeCo). The appearance of the new structure effectively inhibits the collapse of the microstructure of MIL-101(FeCo) during high-temperature pyrolysis, thereby forming a unique FeCo@C core-shell hierarchical structure of FeCo@graphite nanoparticles covered by amorphous carbon. Cobalt doping provides more opportunities to create defects during the alloying process of different metal ions. Additionally, the pyrolysis temperature influences the degree of graphitization of the carbon shell, the number of defects, and the magnetic properties of the alloy. Consequently, the FeCo@C composites exhibit distinguishable reflection loss characteristics that vary with different pyrolysis temperatures. FC-600 and FC-700 obtained at 600 °C and 700 °C showed excellent microwave absorption performance due to their good attenuation ability and outstanding impedance matching characteristics. FC-600 exhibits a broadband absorption of 6.04 GHz covering 8.31–14.35 GHz; the minimum reflection loss of FC-700 reaches −58.61 dB at 12.99 GHz with a thickness of 1.87 mm.