A Janus facilitated transport membrane with asymmetric surface wettability and dense/porous structure: Enabling high stability and separation efficiency

Facilitated transport membranes have been extensively applied in a myriad of industrial fields, in view of their distinctive capabilities of selective separation of target species (e.g., ions/small molecules). Despite much progress, it remains challenging to tackle the trade-off relationship between the stability and separation efficiency of these membranes. Herein, we propose a Janus facilitated transport membrane with asymmetric surface wettability and dense/porous structure by decorating a hydrophilic and dense polymer inclusion membrane (PIM) skin layer on the surface of a hydrophobic and microporous polyvinylidene fluoride (PVDF) membrane to achieve a notable balance between separation efficiency and leakage-resistance. With the hydrophilic PIM skin layer facing aqueous solutions whilst the hydrophobic PVDF membrane towards organic solution during separation process, the Janus facilitated transport membrane remarkably prevents the leakage of the liquids from 66.7% (using the plain PVDF membrane) to negligible. Through a rapid transformation of the transport mechanism from a short-term hopping in the dense PIM skin layer to an unobstructed motion in the microporous PVDF membrane matrix, the separation efficiency of the Janus facilitated transport membrane has been considerably enhanced from 25% (using the PIM) to about 70%. Investigation of the influencing factors on the structures, properties and separation performance of the Janus facilitated transport membrane suggests that the concentration of the PIM casting solution is of particular importance to the formation of the PIM skin layer and the asymmetric dense/porous structure of the membrane. In addition, the Janus facilitated transport membrane exhibits extraordinary mechanical properties and selectivity. Our work demonstrates that the Janus facilitated transport membrane holds great promise and a wide scope in versatile applications in water treatment, water-oil separation, and recovery of metal ions/small molecules in complex systems (e.g., water-oil-metal ions and water-oil-small molecules).