MOF-derived Co nanocages in cellulose‑carbon aerogels enable broadband microwave absorption with thermal insulation

A lightweight, eco-friendly Co@C composite aerogel with a guest–host hierarchical structure is fabricated via freeze drying plus carbonization. ZIF-67 derivatives generate Co nanoparticles and hollow carbon nanocages, producing magnetic loss and strong interfacial polarization. The carboxymethyl cellulose–derived carbon framework builds the aerogel skeleton, reduces heat transfer, and increases the microwave path length through multiscale pores. Co@C-2 delivers an effective absorption bandwidth (EAB) of 8.24 GHz at a thickness of 2.8 mm, whereas Co@C-1 achieves the deepest minimum reflection loss (RL_min) of −53.3 dB at 3.4 mm. When the heating stage is maintained below 300 °C, the upper-surface temperature of the as-prepared Co@C aerogels increases only gradually. This approach offers a practical pathway to lightweight, MOF-derived absorbers that integrate efficient microwave attenuation with thermal insulation.