An ultrathin bilayer membrane with asymmetric wettability for pressure responsive oil/water emulsion separation

Superwetting membranes offer a good platform for oil/water separation, but the generation of responsive membranes for on-demand oil/water emulsion separation with both high permeation flux and selectivity is still a challenge. Herein, bilayer membranes that feature asymmetric wettability across the membrane thickness are constructed, simply by depositing a thin layer of polydopamine-coated single-walled carbon nanotubes (SWCNTs) and subsequently coating with a SWCNT layer. When a low applied pressure difference across the membrane, P_applied, is utilized, the hydrophobic-superoleophilic surface is critical for the separation of surfactant-stabilized water-in-oil emulsions. Triggered by an intensive P_applied, surfactant-stabilized oil-in-water emulsions can also be fully separated by a synergistic effect of dual layers. Such ultrathin bilayer membranes exhibit ultrahigh permeation flux and separation efficiency with excellent antifouling for both water-in-oil and oil-in-water emulsion separation in a single-unit, which is readily achieved by the modulation of P_applied. Therefore, we envision that our bilayer membranes show great potential in oil/water emulsion separation.