One-pot fabrication of hydrophobic, superelastic, harakeke-derived nanocellulose aerogels with excellent shape recovery for oil adsorption and water-in-oil emulsion separation.

Cellulose-based aerogels have attracted significant attention for oil/water separation due to their high porosity, large specific surface area and high adsorption capacity. However, their intrinsic hydrophilicity, and inadequate mechanical properties have often limited their practical applications. Traditional freeze-dried cellulose aerogels exhibit unsatisfactory elasticity and require a separate surface modification process to adjust the surface wettability. In this study, we present a novel one-pot fabrication strategy which simultaneously achieves the crosslinking of individual cellulose nanofibers and the hydrophobic modification of the surface wettability. Following directional freeze-drying, hydrophobic, superelastic, and anisotropic cellulose-based aerogel was prepared from the 2,2,6,6-tetramethylpiperidin-1-oxyl (TEMPO)-oxidized cellulose nanofibers, isolated from harakeke (New Zealand native flax). The resulting aerogel exhibits a high water contact angle of 142°, good compressive recovery performance (85 % recovery of the original height after 100 compression cycles at 70 % strain), and outstanding adsorption capacity for various types of oil and organic solvents (80-105 g/g). Furthermore, the aerogel could also be used as a filter to separate surfactant stabilized water-in-oil emulsions with a high flux (782 L m h) and a high separation efficiency (98.7-99.2 %). The novel aerogel prepared in this study is expected to have great potential for practical applications in oily wastewater remediation.