Highly Porous, Hydrophobic, and Compressible Cellulose Nanocrystals/Poly(vinyl alcohol) Aerogels as Recyclable Absorbents for Oil–Water Separation

This work reports porous and hydrophobic aerogels prepared from cellulose nanocrystals (CNCs) with the assistance of poly(vinyl alcohol) (PVA), followed by thermal chemical vapor deposition of methyltrichlorosilane on the surface. Different from other CNC reinforced materials that cannot be cyclically compressed, these cellulose nanocrystals/PVA aerogels could be compressible for 50 cycles without a significant decrease in mechanical strength, thus demonstrated excellent robustness. With the three-dimensional interconnected microstructure, the aerogels were highly porous (porosity >97.7%) and ultralight with a density ranging from 22.5 to 36.1 mg/cm3 and floatable on the water surface. The wettability test revealed that the aerogel surface was highly hydrophobic with water contact angles up to 144.5°. Notably, the aerogels were capable of absorbing various oils and nonpolar solvents and efficiently separating them from water, with an absorption capacity up to 32.7 times of its original weight. Two facile approaches, including squeezing and washing, were applied to recycle the aerogels. The results demonstrated that the aerogels could be cyclically used at least 10 times without an obvious decrease of the absorption capacity. The as-prepared aerogels show great potential in many engineering and environmental applications, e.g., as recyclable absorbents for water–oil separation.