Chitosan-derived carbon aerogels with multiscale features for efficient microwave absorption

[Display omitted] •Biomass-based N-doped carbon aerogels were designed for microwave absorption (MA).•Superior absorption (-68.8 dB) outperforms other biomass-derived carbon absorbers.•Impedance matching and high attenuation with appropriate dielectric properties.•Synergistic effect of hierarchically optimized structures and inherent N-doping.•Fully taps the potential of microstructure regulation for MA optimization. Remarkable features of lightweight and 3D conductive network make carbon aerogels a competitive candidate for advanced microwave absorption (MA) materials. However, little is known about the specific correlation between multiscale structural parameters and their MA properties, setting obstacles for fully tapping the potential of microstructure regulation. Herein, utilizing sustainable biomass as the precursor, chitosan-derived N-doped carbon aerogels (CCA) with finely-tailored hierarchical structure were fabricated via regulating the freeze casting and annealing processes. Carbonization temperature mainly controlled nanoscale structural features such as defects and nanocrystals which had a significant impact on conductive and polarization losses. As for micron/macro-scale structures, the pore size and 3D conductive network configuration contributed to interfacial polarization and conductive losses, which were regulated by freezing process and precursor concentration. The synergistic effect derived from the hierarchical optimized structure and inherent N-doping was responsible for a remarkable reflection loss of − 68.8 dB, and an effective absorption band covering the whole X-band at 5.1 mm. Such MA performance significantly outperforms other biomass-derived carbon absorbers that usually incorporate magnetic components. The multi-scale structural control implemented in this work is essential to fully exploit the potential of chitosan-derived carbon aerogels across different length scales and design high-performance microwave absorbers.