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.