Bionic fire-resistant chitosan aerogels with the triple stealth functionality: microwaves, infrared and sound

The complex electromagnetic environment in national defense requires tailored microwave-absorbing materials for different scenarios. In aerospace, lightweight and multifunctional materials are especially important. While aerogels offer low density, they must be further modified to become effective microwave absorbers. Traditional fillers like carbon nanotubes often cause problems such as impedance mismatch, particle aggregation, and poor chemical reactivity, limiting their performance in aerogel systems. To overcome these issues, we used an electrostatic self-assembly strategy to deposit a FeCo-based metal-organic framework (MOF) onto black phosphorus nanosheets (BPNSs). The resulting BPNS@MOF was then integrated into a chitosan-derived aerogel through Schiff base reactions between the amino groups of the MOF and the aldehyde groups of glutaraldehyde. After freeze-drying and high-temperature pyrolysis, we obtained a lightweight, multifunctional carbon/BPNS@MOF aerogel (CS-2). CS-2 exhibits excellent electromagnetic properties, with a minimum reflection loss of -72.13 dB and an effective absorption bandwidth of 5.88 GHz. Radar cross-section simulations confirm its stealth potential. In addition, CS-2 shows ultralow thermal conductivity (0.05 W (m K)^-1), superior fire resistance, and outstanding sound absorption performance (a 5.0 mm-thick sample achieves a sound absorption coefficient of above 0.95). These features demonstrate its strong potential for multifunctional aerospace and defense applications.