Miniaturized Hard Carbon Nanofiber Aerogels: From Multiscale Electromagnetic Response Manipulation to Integrated Multifunctional Absorbers

The multiscale structural engineering strategy presents a powerful method for tailoring the structural attributes of materials at various levels, enabling the flexible control and manipulation of their electromagnetic properties. Nonetheless, orchestrating the multiscale architecture of polymer-derived carbon aerogels specifically for microwave absorption poses significant challenges. Herein, aramid-derived hard carbon nanofiber aerogel microspheres (CNFAMs) featuring a hierarchical skin-core structure are fabricated through a wet-spinning technique, combined with reprotonation-mediated self-assembly and carbonization processes. The presence of large-scale voids between neighboring microspheres and the microscale porosity within the microspheres themselves improves impedance matching and promotes microwave reflection and scattering. The distinct graphitic domains and defects serve as pivotal elements for conduction and polarization losses, significantly impacting microwave attenuation. By meticulously tailoring the macroscale dimensions, microscale porous architecture, and nanoscale domains, the optimized CNFAMs demonstrate a remarkable absorption bandwidth of 9.62 GHz at an ultralow filling of 0.97 wt%. Additionally, the implementation of application-oriented microwave absorption through the innovative integration of polysilsesquioxane-CNFAMs in a host–guest aerogel is explored. This composite system brings together broadband absorption, superhydrophobicity, thermal insulation, resistance to freezing, and robust tolerance to harsh environments. Such a multifaceted approach is designed to tackle the growing challenges associated with complex electromagnetic environments effectively.