Ultrathin coordination-crosslinked nacre-inspired hydrogel superwetting membranes with enhanced mechanical stability for high-performance emulsion separation

Superwetting membranes have considerable potentials in the field of water treatment, especially for oil-water separation, however it still keeps great challenges to prepare ones with high mechanical property and strong interfacial cohesion strength. Herein, inspired by high hardness yet toughness of natural nacre, we proposed a polyphenol-mediated inner-outer through type modification strategy to fabricate ultrathin coordination-crosslinked nacre-inspired hydrogel superwetting membranes (named PVDF/GPT/Fe), using 2D graphene oxide (GO) nanosheets, flexible polyvinyl alcohol (PVA) and branched structure tannic acid (TA) as the assembly units, and Fe3+ ion as the cross-linking agent. It is found that PVA-TA interface assembly is key to realize the inner-outer through type hydrophilic modification for the hydrophobic PVDF membrane, to achieve superhydrophilicity and underwater superoleophobicity with the UOCAs of above 150°, ultra-low oil-adhesion and self-cleaning property, with a high flux recovery ratio of 96.3 % after six cycles. The PVDF/GPT/Fe membrane exhibits the boosted mechanical strength and damage resistance, with the Young's modulus of up to 1076 MPa, which is enhanced by 4.4 times, compared to the pristine PVDF membrane, benefiting from the formation of the layered brick-and-mortar structured nacre-inspired hydrogel coating and strong bonding strength of the interfaces between the base membrane and the top coating layer. The separation efficiencies of the PVDF/GPT/Fe membrane for various oil-in-water emulsions are higher than 99.5 % and the largest emulsion permeance is 611.2 L m-2 h-1 bar-1. Our research extends the path route to design and manufacture novel biomimetic superwetting membranes with high mechanical strength and durability.