Abstract: Developing high-efficiency electromagnetic wave (EMW) absorbers by designing dielectric/magnetic components and microstructure in a straightforward, scalable method is highly desirable yet challenging. Here, we introduce a novel hierarchical composite aerogel-based EMW absorber composed of conductive carbon nanotubes (CNTs) and magnetic metal-organic framework (MOF) derivatives, integrated with sustainable cellulose nanofibers (CNF) derived carbon. This composite was prepared using a scalable freeze-casting followed by carbonization approach. Freeze casting enabled the creation of porous monoliths with high specific surface areas and customizable pore sizes and porosities, crucial for enhancing EMW reflection and scattering. Carbonization enhanced composite conductivity and stabilized the cobalt (Co)/carbon nanoparticles derived from ZIF-67 within the carbon matrix. CNF-derived carbon facilitated the efficient integration of ZIF-derived Co nanoparticles and CNTs, resulting in a robust 3D aerogel structure. The synergistic effects of CNT conductive paths and Co nanoparticles' magnetic losses provided an efficient route to enhance EMW absorption. Moreover, the creation of numerous heterogeneous interfaces augmented polarization losses, significantly enhancing EMW loss capability. Remarkably, the composite achieved outstanding EMW absorption, with a minimum reflection loss of -71.03 dB at a filling ratio of merely 10 wt.% and an effective absorption bandwidth of 4.64 GHz, comparable to leading EMW absorbers reported to date.

Key words: Aerogel, Carbon nanotubes, Impedance matching, ZIF-67, Electromagnetic wave absorption