Scalable manufacturing of light, multifunctional cellulose nanofiber aerogel sphere with tunable microstructure for microwave absorption

Thanks to the high strength-to-weight ratio and aspect ratio, large specific surface area, and sustainability, cellulose nanofibers (CNFs) have incomparable advantages in constructing multifunctional aerogels. However, efficient utilization of the nanofibrous microstructure for developing aerogels of high-performance is extremely challenging due to the severe agglomeration of CNF. Here, a novel type of ultralight aerogel spheres composed of fibrous or sheet-like CNF-derived nanocarbon are manufactured via a facile, scalable drop-freezing followed by a pyrolysis approach. The nanostructured carbons of tunable morphologies are accomplished, endowing the aerogel spheres with abundant hierarchical pores, large specific surface area, and three-dimensional conductive skeletons with ultralight nature. In addition to the high-efficiency adsorption of the organic dye, the aerogel spheres enable a controllable and excellent electromagnetic wave absorption. The aerogels composed of coexisting fibrous and layered nanocarbons display an effective absorption bandwidth of 6.16 GHz, and a minimum reflection loss of −66.3 dB at the thickness of 2.14 mm, and a merely 1 wt% filler loading, which significantly outperforms that of other carbon-based absorbers. This work thus suggests a new avenue for designing high-performance, sustainable multifunctional biomass-based aerogels, demonstrating extensive application potentials in adsorption, electromagnetic absorption, and aerospace.