Super-elastic and highly hydrophobic/superoleophilic sodium alginate/cellulose aerogel for oil/water separation

To overcome the poor mechanical properties of biomass aerogels in oil/water separations, three different freeze-casting methods were used including direct freezing, unidirectional freezing, and bidirectional freezing with sodium alginate (SA) aerogels reinforced with cellulose nanofibrils (CN). After chemical crosslinking and silane modification, compression testing revealed that the SA/CN aerogels with parallel lamellar microstructures prepared by bidirectional freezing exhibited super-elasticity with the minimal energy dissipation of ~ 0.04 in each cycle, a maximum compressive stress of 80.4 kPa, and minimal plastic deformation at ~ 4.15%. Additionally, the water and oil contact angle of the surface of the lamellar SA/CN aerogel was 148.7° and 0°, respectively. By combining the super-elasticity and hydrophobicity/superoleophilicity, the lamella SA/CN aerogels could be reused for the separation of oil/water mixture with oil absorption capacities up to 34 times its weight. Furthermore, the lamellar SA/CN aerogel could continuously separate oil/water mixtures with the assistance of a pump. Therefore, the present study offers a simple and environmentally friendly method for fabrication of super-elastic and hydrophobic/superoleophilic biomass aerogels that are applied to continuous removal of oil from water.