Durable PVA-based hydrogel sponge with cellulose whiskers embedded in the 3D interconnected channels for efficient oil/water separation.

Superhydrophilic hydrogel was typically used as the membrane coating on various substrates for oil/water separation. Nevertheless, these coatings may suffer from such limitations as poor adhesion strength and abrasion-resistance. Thus, the facile construction of hydrogel sponge with 3D connecting channels would be an ideal choice. Herein, we reported a free-standing polyvinyl alcohol (PVA)/cellulose nanocrystal (CNC) hydrogel sponge for controllable oil/water separation. In the design, the salt/CNC hybrid crystals instead of conventional salt particles were employed as the sacrificial template, thus CNC was creatively integrated into the long and tortuous 3D interconnected channels via the solvent displacement combined template-leaching strategy. The resultant microstructure woven by CNC bundles in sponge channels could alleviate severe pore collapse in leaching process and oil intrusion. Moreover, it could serve as the superhydrophilic "sieve", promoting the separation efficiency significantly. The gravity-based separation efficiencies for PC-HL hydrogel sponge in processing of diverse oil/water mixture and oil-in-water emulsions could achieve up to 99.7 and 99.4 %, respectively. In addition, this hydrogel sponge can be used for continuous oil/water separation without obvious decline upon several cycles. This work provides a different way to fabricate the eco-friendly, low-cost and energy-saving filtration hydrogel sponge, showing high potential in oily wastewater treatment.