Lightweight chitosan-derived carbon/rGO aerogels loaded with hollow Co1-xNixO nanocubes for superior electromagnetic wave absorption and heat insulation

Designing lightweight electromagnetic (EMW) absorption materials with an ultra-broad effective absorption bandwidth (EAB), strong reflection loss (RL), and low filling level remains a challenging. In this study, an anisotropic chitosan-derived carbon/reduced graphene oxide (rGO) aerogel loaded with hollow ZIF-67 nanocubes (CG3) was constructed via unidirectional freeze-drying, heat treatment, and in situ ZIF-67 growth, followed by chemical etching. The interconnected oriented cell walls, hollow ZIF-67 nanocubes, and heterogeneous carbon/rGO interfaces enhanced EMW absorption as a result perfect impedance matching, multiple scattering, and strong dielectric polarizations. Thus, an outstanding EMW absorption performance with an ultra-broad EAB of 9.5 GHz and a minimal RL (RLmin) of -53.3 dB was achieved for the CG3 aerogel with an ultra-low filling ratio (5.5 wt%). Further, to integrate strong EMW absorption and heat insulation abilities, the hollow ZIF-67 nanocubes loaded on the carbon/rGO aerogel were converted into hollow Co1-xNixO nanocubes (CG4) via a cation exchange reaction and annealing treatment in air. Owing to the oriented pore structure, the CG4 aerogel exhibited obviously anisotropic EMW absorption and heat insulation. When the CG4 aerogel was cut along the longitudinal section parallel to the direction of ice crystal growth (CG4-L), a tubelike porous structure was revealed, and this endowed the aerogel with the highest EMW absorption (EAB = 8.7 GHz, RLmin = -52.3 dB) and thermal insulation (thermal conductivity = 0.057 W m-1 K-1) performance because of the extended EMW transmission and thermal transfer pathways. Thus, this work offers an important design strategy for obtaining high-performance thermally insulating, EMW-absorbing composites.