Core-shell BCNO@Fe3O4 ceramics for impedance matching and synergistic microwave absorption with improved thermal management

BCNO@Fe 3 O 4 core-shell composites were constructed using corn silk-derived biomass carbon as a template. • BFeO-2 achieves an RLmin of −56.5 dB at 7.23 GHz and a 2.5 GHz EAB in the low-frequency region. • Fe 3 O 4 regulation balances dielectric-magnetic loss, impedance matching, and thermal conduction. The integration of high-power electronic devices has intensified both electromagnetic interference and heat accumulation, creating an urgent need for bifunctional materials with efficient microwave absorption and thermal management capabilities. In this work, a C- and O-doped boron nitride ceramic framework (BCNO) was first prepared using corn silk-derived biomass carbon as a template, followed by the deposition of Fe 3 O 4 on the BCNO surface through a solvothermal process to construct BCNO@Fe 3 O 4 (BFeO) core-shell composites. By tuning the Fe 3 O 4 content, the effects of composition and microstructure on electromagnetic response and heat conduction were systematically investigated. The results showed that the optimized samples exhibited strong microwave absorption in the low-frequency region. BFeO-2 delivered a minimum reflection loss (RL min ) of −56.5 dB at 7.23 GHz with an effective absorption bandwidth (EAB) of 2.5 GHz (5.8-8.3 GHz), while BFeO-3 achieved a RL min of −58.3 dB at 6.34 GHz. The enhanced absorption originated from the synergistic effects of interfacial polarization, dipolar polarization, magnetic loss, and multiple reflection/scattering enabled by the core-shell heterostructure. In addition, BFeO also showed a significant thermal conduction enhancement in epoxy. At a filler loading of 30 wt%, the thermal conductivity (TC) of the composites reached 1.62 W m −1  K −1 , corresponding to increases of 540.3% compared with pure epoxy. This study demonstrates that rational regulation of the BCNO/Fe 3 O 4 heterostructure is an effective strategy for developing microwave absorbers with integrated thermal management functionality.