Bio-carbon@Fe/SiO₂ composites: enhanced electromagnetic wave absorption through interface engineering and impedance matching

Bio-carbon wave-absorbing materials have received increasing attention for their potential applications in the field of electromagnetic absorption. Although abundant and environmentally friendly, these bio-carbon materials typically exhibit a high dielectric constant and poor impedance matching, which significantly limits their microwave absorption capabilities. In this study, bamboo charcoal (BC)/Fe composite wave-absorbing materials were initially prepared via a carbonization‒impregnation‒carbonization method, followed by coating of SiO₂ using Stöber's method. XRD, SEM, TEM, XPS, VSM and VNA were employed for sample detection and characterization. The results demonstrate that an appropriate amount of SiO₂ coating can enhance the impedance matching of the composites, leading to a significant improvement in electromagnetic wave absorption. The optimal wave-absorbing performance of the BC/Fe/SiO₂ composite was achieved at an ethanol to tetraethyl orthosilicate volume ratio of 80:1. The composite exhibited a coercivity of 61.1 Oe and a saturation magnetization of 3.53 emu/g. At a matched thickness of 5 mm, the minimum reflection loss reached −41.68 dB, with an effective absorption bandwidth of 1.28 GHz. Analyses revealed that the high porosity of the carbonized composites, along with their heterogeneous interfaces and the synergistic effects of multiple loss mechanisms, contributed to their effective attenuation of electromagnetic waves. The outstanding wave-absorbing properties of this bio-carbon-based ternary composite suggest promising applications in both civil and military electromagnetic wave absorption fields.