C nanofibers dotted with metal–organic framework (MOF)-derived square Fe@C crystals for enhanced electromagnetic wave absorption performance

C nanofibers dotted with square Fe@C crystals derived from metal–organic frameworks (MOFs) with a novel 3D hierarchical architecture were successfully prepared through electrospinning, hydrothermal processing, and high-temperature pyrolysis. The introduction of carbon nanofibers endowed the particles with directional action and mechanical support, inhibiting local agglomeration and the collapse of the Fe@C crystals. The unique overall 3D porous structure with micro-concavities on its surface provided sufficient paths for electromagnetic wave transmission, abundant heterostructured interfaces for interfacial polarization and a connected network for conductive loss. The appropriate combination of the magnetic Fe@C crystals with dielectric carbon nanofibers optimized the impedance matching. Benefitting from the ingenious design, the composites exhibited excellent electromagnetic wave absorption (EWA) performances. FC1–30 was found to exhibit a minimum reflection loss (RLmin) of −28.09 dB at a thickness of 5.5 mm and a widest effective absorption bandwidth (EAB) of 1.1 GHz at a thickness of 2.5 mm. FC1–10 showed a RLmin of −20.82 dB at a thickness of 3.0 mm and a broadest EAB of 3.8 GHz at a thickness of only 1.5 mm. The preparation process was optimized, and the influence of the filler loading ratio on EWA performance was investigated. The EWA mechanism has been discussed in detail. The study provides an opportunity for the development of advanced electromagnetic devices with integrated structure and function.