Janus membranes for fast-mass-transfer separation of viscous ionic liquids from emulsions

Abstract

Separation membranes are urgently desired for the efficient recovery of oil-like ionic liquids (ILs) from industrially applied emulsions. Conventional membranes with asymmetric porous structure and high tortuosity suffer from high trans-membrane resistance and low mass transfer efficiency for this application. Herein, Janus membranes (JMs) are constructed by the single-side modification of hydrophobic poly(vinylidene fluoride) (PVDF) membrane with vertically penetrative pores for the rapid-mass-transfer separation of viscous ILs. A charged and underwater IL-phobic thin layer is facilely co-deposited on one side of the PVDF membranes from polydopamine/poly(diallyldimethylammonium chloride) solution. This single-side modification endows the as-prepared JMs with a deemulsification function to IL-in-water emulsions and a unidirectional transportation ability to hydrophobic ILs. These JMs show an excellent IL recovery capacity with high permeation speed and stable flux during a long-term cyclic separation of IL-in-water emulsions because the vertically penetrative pores with low tortuosity allow to significantly reduce the trans-membrane resistance toward those viscous ILs. Overall, our vertically-channeled JMs provide an ideal material solution for recovering high-viscosity and value-added chemicals from their industrial water mixture in practice, especially from those aqueous emulsions.