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A model of the coexistence of superhydrophilicity and superoleophobicity with elaborate experimental proofs.

Materials that possess distinguishable superwettability toward oil and water have aroused widespread attention for their application in oil–water separation. Among them, a superoleophobic/superhydrophilic material is considered as the ideal candidate because of its antioil-fouling and water-wetting behavior; however, the fabrication is a challenge and there has been insufficient attention given to multipurpose applications in treating intricate mixtures. Herein, for the first time, a multifunctional superoleophobic/superhydrophilic coating integrated with a photocatalysis property was fabricated by the combination of polarity component-enhanced fluorosurfactant and titanium dioxide (TiO2) nanoparticles. The coating applied on stainless steel mesh preserves the ability to separate immiscible oil–water mixtures, whereas the coated cotton preserves the ability to separate both surfactant-stabilized oil-in-water and water-in-oil emulsions. Notably, benefiting from the photocatalysis property of titanium dioxide, the coating also can be used in liquid purification. Contaminated oil can be separated and purified by a separation–purification process, during which the oil-soluble contamination is degraded under ultraviolet (UV) irradiation. The multipurpose coating provides an alternative solution for oil–water remediations, which has prospects in intricate liquid treatment in industrial and domestic applications.

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The superoleophobic/superhydrophilic material has attracted considerable interest due to the incomparable property of it for the oil–water separation. However, it is a challenge to make the prepared surface superoleophobic and superhydrophilic at the same time since the oleophobic surface tends to repel water. Herein, a hygro-responsive superoleophobic/superhydrophilic coating was fabricated by liquid-phase deposition of TiO2 with perfluorooctanoic acid. The wettability of the coating could complete the transformation from superoleophobicity/superhydrophilicity to superhydrophobicity/superoleophilicity, both of which exhibit excellent selective superwettability under the air, underwater, salt, alkali, and acid conditions. The hygro-responsive coating can separate different types of oil–water mixtures, and the separation efficiency could be over 99% using different capillary forces acting on the oil and water phases before and after wettability transformation. Last but not least, long-chain perfluoroalkyl substances on the coating could be decomposed by UV irradiation, which could reduce the harm to the environment and human beings. It is anticipated that the developed superoleophobic/superhydrophilic coating provides a feasible solution for the application of oil–water separation.