A bionic Janus membrane with spindle knots and ultra-high separation efficiency for various oil–water mixtures

Due to the prominent membrane interface effect micro-oil or micro-water droplets are easily fused with water or oil and are difficult to separate. The size of underwater/underoil droplets varies greatly, it needs a functional membrane for separating various oil–water mixtures. A novel bionic Janus membrane with a superhydrophobic spindle knots structure was prepared by a one-step dual-axis electrospinning technique. The Janus membrane relying on liquid unidirectional permeation achieves the separation of various oil–water mixtures including light/heavy oils-water, oil-in-water, and water-in-oil emulsions. Accordingly, it can be designed as an underoil diode water collector without any leakage. Importantly, the spindle knots absorb, transport and coalesce the micro-oil droplets into large oil droplets during separating oil-in-water emulsion, whereas it can repel water adhesion and allow oil spreading during separating water-in-oil emulsion. Thus, the spindle knots endow the ultra-high interface oil–water mixture, various emulsions separation efficiency (interface oil: >99.8 %, oil-in-water emulsion: 99.5 %, water-in-oil emulsion: 99.2 %), and excellent antifouling properties of Janus membranes for underwater oil and underoil water. This bionic Janus membrane presents a wide application in smart oil–water separation equipment, biomedical microreactors, and flotation filtration devices.