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A facile and efficient strategy for constructing anti-oil-fouling zwitterionic coatings on membranes is developed. The resultant membrane exhibits excellent anti-oil-fouling ability even in a dry state, and has a high efficiency for emulsion separation with a high flux of 5800 L m−2 h−1 bar−1 and an oil rejection of up to 99.6%. [ABSTRACT FROM AUTHOR]

[Display omitted] • The process for constructing nanostructured hydrogel is simple and time-saving (<10 min) • The method is green and mild, without cumbersome surface activation process. • Nanostructure is generated by in-situ growth, without adding extra nanomaterials. • The strategy can transform various hydrophobic membranes into superhydrophilic ones. • The resultant membrane exhibits excellent anti-crude oil-adhesion property. 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. [ABSTRACT FROM AUTHOR]

Tannic acid-based functional coatings, as a green, universal and versatile tool to manipulate surface properties, have received extensive attention in the field of surface engineering of membranes for oil-in-water emulsion separation. With the rapid development of this field, more flexible and efficient modification strategies for surface engineering of membranes have been developed recently. It is therefore critical to update the broader scientific community on the important advances in this field. Here, we summarize recent progress in surface engineering of membranes with tannic acid-based coatings for oil-in-water emulsion separation. The chemical properties of tannic acid and how to design TA-based functioanl coatings via physical/chemical regulation are discussed. The roles of tannic acid in surface engineering of membranes are highlighted and classified into the following five categories: changing surface wettability, adjusting surface charge, constructing catalytic surfaces, forming hydrogel surfaces, and fabricating hybrid separation membranes/layers. Finally, the future outlook and the challenges in this field are discussed. [ABSTRACT FROM AUTHOR]