Hetero–interface engineering of biomass carbon foam for broadband microwave absorption and thermal insulation properties

Hetero-interface engineering of biomass carbon foam offers great potential for the innovation of lightweight, broadband electromagnetic (EM) wave absorption and thermal insulation materials. In this work, micro/macro three-dimensional (3D) network biomass carbon foams decorated with elliptical and nanoparticle TiO₂ structures derived from eggplant were prepared through freeze-drying, carbonization, and heat treatment processes. The distinctive structure promotes impedance matching, along with the reflection and scattering of EM waves. Additionally, the elliptical and nanoparticle TiO₂ are evenly distributed on the surface of the layered carbon foam, forming numerous hetero-interfaces that strengthen the interfacial polarization. The results show that the QT-3 sample (at 900 °C) achieved a minimum reflection loss (RL_min) of −28.41 dB at a 3.1 mm thickness, along with a broad effective absorption bandwidth (EAB) of 6.5 GHz (from 11.5 to 18 GHz) at 2.0 mm, covering the entire Ku band. Furthermore, within the detection angle range of 0°–90°, the radar cross-section (RCS) is reduced by more than 10 dB m². Furthermore, the infrared stealth performance has been validated: it maintains a surface color consistent with the surrounding environment. Moreover, the surface of the QT-3 sample leveled off at 31.1 °C (in 50 min) when heated on a 112 °C heating plate. Therefore, the cooperative relationship between TiO₂ and carbon foam achieves multifunctional performance, including excellent EM wave absorption, superior infrared stealth, and thermal insulation properties, paving the way for the application of advanced stealth materials in complex and harsh environments.