Janus Membranes with Asymmetric Wettability Applied in Oil/Water Emulsion Separations

With frequent oil spill accidents and the large amount of oily wastewater produced in various industrial and domestic processes, the separation of emulsified oil/water mixtures has become an important topic in environmental protection. Janus membranes with asymmetric wettability stand out among many separation materials for their switchable separation, high separation efficiency, low energy consumption, good repeatability, and durability. In recent years, Janus membranes have developed rapidly, but their separation principles and advantages and disadvantages compared with other separation methods in oil/water emulsion are rarely reviewed. Here, the classification of Janus membranes based on special wettability is summarized. According to the different separation principles, this paper focuses on the research and application of Janus membranes in oil/water emulsions based on the size sieving effect, the charge-screening effect, coalescence, and differential pressure. The advantages and disadvantages of Janus membrane application in oil/water emulsion are shown after comparing with the separation materials based on filtration, absorption, and electric demulsification. Finally, some challenges and prospects are presented for the future development of Janus membranes.