Highly Compressible Wood Sponges with a Spring-like Lamellar Structure as Effective and Reusable Oil Absorbents

Aerogels derived from nanocellulose have emerged as attractive absorbents for cleaning up oil spills and organic pollutants due to their lightweight, exceptional absorption capacity, and sustainability. However, the majority of the nanocellulose aerogels based on the bottom-up fabrication process still lack sufficient mechanical robustness because of their disordered architecture with randomly assembled cellulose nanofibrils, which is an obstacle to their practical application as oil absorbents. Herein, we report an effective strategy to create anisotropic cellulose-based wood sponges with a special spring-like lamellar structure directly from natural balsa wood. The selective removal of lignin and hemicelluloses via chemical treatment broke the thin cell walls of natural wood, leading to a lamellar structure with wave-like stacked layers upon freeze-drying. A subsequent silylation reaction allowed the growth of polysiloxane coatings on the skeleton surface. The resulting silylated wood sponge exhibited high mechanical compressibility (reversible compression of 60%) and elastic recovery (∼99% height retention after 100 cycles at 40% strain). The wood sponge showed excellent oil/water absorption selectivity with a high oil absorption capacity of 41 g g^-1. Moreover, the absorbed oils can be recovered by simple mechanical squeezing, and the porous sponge maintained a high oil-absorption capacity upon multiple squeezing-absorption cycles, displaying excellent recyclability. Taking advantage of the unidirectional liquid transport of the porous sponge, an oil-collecting device was successfully designed to continuously separate contaminants from water. Such an easy, low-cost, and scalable top-down approach holds great potential for developing effective and reusable oil absorbents for oil/water separation.