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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]

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]

Underwater superoleophobic and underoil superhydrophobic materials have distinct advantages for switchable oil–water separation. Although some strategies have been developed to fabricate these materials, harsh conditions such as high temperature and pressure, abundant harmful organic solvents and complicated devices are usually needed, limiting their practical applications. Moreover, due to the high adhesion properties of some oils such as crude oil, the anti-viscous oil-fouling performance of usual superwetting material is still unsatisfactory. Herein, based on the corrosion process and mussel-inspired surface coating, we have developed a mild and eco-friendly route to transform iron meshes into underwater superoleophobic and underoil superhydrophobic materials for switchable high viscosity oil–water separation. The corrosion process can generate microsphere-nanosheet structures (MNS) composed of microspheres and abundant nanosheet arrays on the iron mesh surface, while the subsequent mussel-inspired surface coating can form a compact layer to protect the MNS from damage, finally endowing the resultant mesh with durable underwater superoleophobicity and underoil superhydrophobicity. Significantly, the resultant mesh exhibits excellent anti-crude oil-fouling properties, and can separate various oil–water mixtures with high efficiency (all above 98%). Moreover, after immersion in acidic or basic solutions, the wetting properties of the mesh showed no apparent variation, demonstrating that the mesh possesses a desirable environmental stability. According to the dual superlyophobic properties of the as-prepared mesh in water–oil systems, a dual-channel device has been designed to realize the continuous separation of the crude oil–water mixture with high efficiency (above 93% after 30 cycles). This strategy may open a new avenue to prepare high-performance separation materials for viscosity oil–water separation. [ABSTRACT FROM AUTHOR]