Ambient-drying to construct unidirectional cellulose nanofibers/ carbon nanotubes aerogel with ultra-lightweight, robust, and superior microwave absorption performance

Microwave absorption materials (MAMs) with lightweight wide effective absorption band, superb mechanical performance, and capable of large-scale preparation are highly desirable for dealing with microwave pollution, but it is still a challenge to realize these performances simultaneously on one material. Herein, we report an ambient drying and non-chemical cross-linking way of preparing high-performance microwave absorption aerogels from cellulose nanofibers (CNF) and carbon nanotubes (CNT). Anisotropic aerogel pore walls with excellent mechanical properties can be constructed by unidirectional cycling freeze-thaw to cross-linking CNF and CNT. During this process, a sustainable bioinspired dual-networks interpenetrating strategy is constructed by benefiting from the mono-dispersion of CNF and CNT, thus enabling the creation of hybrid dual-networks of hydrophobic/hydrophilic nanofibers. Impressively, it is found that the dual-networks induced anisotropic aerogel structure and dense pore walls can synergistically result in favorable mechanical properties. In detail, aerogels with tunable ultralow densities (0.0262–0.0296 g cm⁻³), high mechanical properties (the stress of the sample reaches up to 329.8 kPa at 75% strain) and low shrinkage (∼10%) can be prepared. Besides, the aerogels behave a large-scale production future (diameter of aerogel up to 9.24 cm). The as-prepared aerogel delivers a remarkable minimal reflection loss (RL_min) of −60.22 dB at 13.012 GHz and a wide effective absorption bandwidth (EAB) from 2.163 to 18 GHz (15.84 GHz) at a thin thickness of 7.46 mm, which covers almost all the S, C, X, and Ku bands. This work provides a strategy to prepare lightweight and efficient microwave absorbers, as well as illustrates good impedance matching and moderate dielectric loss capability.