Bio-inspired surface engineering of hydrophobic membranes with nano-structured hydrogel toward viscous oil-in-water emulsion separation

Oil-fouling is a troublesome problem for membrane separating viscous oil-in-water emulsions. Nano-structured hydrogel is a superhydrophilic material showing a superior anti-oil fouling property, but the current modification strategies for constructing nano-structured hydrogels on membranes are limited by the complex manipulation and poor universality. In this work, inspired by the stickiness of ovalbumin (OVA) and the versatility of tannic acid (TA), we designed a green, facile and universal strategy for constructing nano-structured hydrogel on various hydrophobic membranes for separating viscous oil-in-water emulsion. Thanks to the distinct adhesion property and reactivity of OVA and TA, cumbersome surface activation process is avoided. What’s more, abundant nano-structure can be generated in-situ during the formation of hydrogel, without adding extra nanomaterials. Compared to the hydrogel without nano-structure, the nano-structured hydrogel can keep un-fouling even the surface was pressed by crude oil for 23 h, demonstrating that the in-situ nano-structure can endow the membrane with excellent anti-crude oil-fouling performance. The resulted membrane not only shows a high efficiency for separating surfactant-stabilized crude oil-in-water emulsion with average flux of 2198 L m−2h−1 bar−1 and crude oil rejection rate of 99.8%, but also shows excellent resistance to water flushing, acid and alkali, and long-time stability in air. Notably, this strategy can construct nano-structured hydrogel on various hydrophobic membranes easily. Considering the simplicity and universality, this strategy has the potential to be a powerful tool for preparing separation membranes with super-anti-high-viscosity oil contamination property and accelerate the rapid development of membrane in separating viscous oil-in-water emulsions.