Conjugated Microporous\nPolymer-Derived Nitrogen-Doped\nCarbon Nanocomposites with Multiple Magnetic Components for Broadband\nMicrowave Absorption

Lightweight magnetic-carbon nanocomposites with multiple\nmagnetic\ncomponents are highly desirable for their efficacy in broadband microwave\nabsorption. However, fabricating such composites with rationally designed\nchemical composites, tailored microstructure, and uniformly distributed\nmagnetic components remains a grand challenge using conventional carbon\nprecursors. Herein, we report the facile fabrication of porous N-doped\ncarbon nanocomposites (Fe<sub>3</sub>O<sub>4</sub>@FeCN) with uniformly\ndistributed and multiple magnetic components of Fe/Fe<sub>3</sub>C/Fe<sub>3</sub>O<sub>4</sub> nanoparticles using conjugated microporous polymers\n(CMPs) as the carbon precursor. CMPs have a high specific surface\narea and abundant nanoporosity, facilitating the efficient loading\nof iron ions and uniform growth of magnetic nanoparticles inside the\ncarbon matrix. Notably, Fe<sub>3</sub>O<sub>4</sub>@FeCN-2 demonstrates\nexcellent absorption capabilities with a minimum reflection loss (RL<sub>min</sub>) of −49.68 dB and a wide absorption bandwidth of\n5.72 GHz at a matching thickness of only 2.0 mm. This outstanding\nmicrowave absorption performance is primarily attributed to the synergistic\neffects of significantly improved impedance matching, enhanced polarization\nloss, and the introduction of magnetic loss through uniformly embedded\nFe/Fe<sub>3</sub>C/Fe<sub>3</sub>O<sub>4</sub> nanoparticles in the\nnanoporous carbon matrix. Moreover, through simulation using computer\nsimulation technology (CST), Fe<sub>3</sub>O<sub>4</sub>@FeCN-2 shows\na significantly reduced radar cross section (RCS), with RCS values\n<−10 dB covering the entire frequency band of 2–18\nGHz at angles of 30, 60, and 90°, demonstrating its great potential\napplications in radar systems and stealth technology. This work will\ninspire the development of carbon precursors to fabricate lightweight\nmagnetic-carbon nanocomposites with precisely controlled structures\nfor high-performance microwave absorption.