Ordered Interfacial Water Generated at Poly(ionic liquid) Membrane Surface Imparts Ultrafast Water Transport and Superoleophobicity

Achieving ultrahigh permeance and superoleophobicity is crucial for membrane application. Here, we demonstrated that a poly(ionic liquid)/PES hydrogel membrane can achieve dual goals. The high polarity of the ionic liquids induces the water molecules on the membrane surface to be arranged more ordered, as verified by molecular dynamics (MD) simulation and advanced femtosecond sum frequency generation (SFG) vibrational spectroscopy. Meanwhile, a large amount of water exists in membrane pores, demonstrated by water absorption, low-field nuclear magnetic resonance, and SFG spectroscopy. The interfacial water layer endows the membrane with superior anti-oil-fouling properties, and the large amount of water in membrane pores imparts membrane with ultrahigh permeability. The positive charge on the channel surface and moderate channel size confer a high rejection of metal ions. The optimal membrane exhibited a permeance of 35.1 L m^-2 h^-1 bar^-1, 5-10 times that of conventional hydrogel membranes with similar rejection. Moreover, the membrane exhibited excellent antibacterial properties. It can be expected that highly polar poly(ionic liquid) membranes will find promising applications in the water treatment field.