Multifunctional ultralight Fe₃O₄/α-Fe/bamboo composites for high-performance microwave absorption, hydrophobicity,...

Developing lightweight, sustainable, and multifunctional electromagnetic wave (EMW) absorbing materials is essential for next-generation electronic devices operating under complex environmental conditions. Herein, a series of ultralight Fe₃O₄/α-Fe/bamboo-derived magnetic carbon composites (MB-600 to MB-900) were fabricated through delignification, precursor impregnation, and in-situ pyrolysis. The hierarchical porous architecture of bamboo, coupled with uniformly distributed magnetic nanoparticles, enables excellent impedance matching and enhances synergistic dielectric, magnetic, and conductive losses. Among the samples, MB-800 exhibits the most remarkable microwave absorption performance, achieving a minimum reflection loss of -71.4 dB at 9.36 GHz with a thin matching thickness of 1.7 mm, and providing an effective absorption bandwidth of 5.76 GHz. Simulation results further confirm that MB-800 significantly reduces monostatic radar cross-section over a wide angular range, demonstrating its strong radar-stealth capability. Moreover, increasing the filler loading boosts electrical conductivity and results in high EMI shielding efficiency dominated by absorption. Benefiting from its highly porous and graphitized carbon-magnetic heterostructure, the composite also exhibits low density (0.47 g/cm³), outstanding hydrophobicity (117.7°), superior thermal safety, and rapid Joule-heating response (151 °C within 10 s at 5 V). This work presents a green and scalable strategy for producing biomass-derived multifunctional magnetic composites, offering promising potential for electromagnetic stealth, EMI shielding, and thermal-management applications.