Current research situation and future prospect of superwetting smart oil/water separation materials

Abstract

Developing advanced superwetting oil/water separation materials with controlled wettability, excellent selectivity and sustainable separation is a persistent pursuit for researchers. Recently, smart materials have been highly anticipated to enable the sustainable treatment of oil spills and oily wastewater. According to their different response mechanisms, smart materials are mainly divided into stimulus responsive and prewetting induced types. The stimulus responsive smart materials can reversibly switch interfacial wettability between superhydrophobicity and superhydrophilicity in accordance with the external stimulus. Alternatively, prewetting induced smart materials can realize on-demand oil/water separation without continuous external stimulus, given that their responses are only water or oil, which can be obtained directly from oil/water mixtures. Even though most smart materials have exhibited remarkable potential in sustainably solving oil spills and purifying oily wastewater, these extremely significant and crucial research advancements have rarely been summarized and reported in the recent literature. Herein, we present an in-depth discussion and systematic summary of the work done thus far in the development of smart materials for oil/water separation. Firstly, the fundamental theory of special wettability, the mechanism of oil/water separation, and the “oil-removing” materials and “water-removing” materials with single wettability are discussed, respectively. Then, Janus materials with asymmetrical wettability are also discussed. Particularly, the current developments of smart materials with switchable wettability are emphatically reviewed, such as their preparation principles, main responsive factors, representative works, design ideas, fabrication strategies, and the role of special wettability in oil/water separation. Finally, a comprehensive summary and future outlook of smart materials are provided, including their advantages and disadvantages, the remaining challenges, and prospects for the future of this subject. It is expected that this comprehensive overview will provide a fresh understanding and important guidance for future research on smart oil/water separation materials.