Constructing A Janus membrane with extremely asymmetric wettability for water unidirectional permeation and switchable emulsion separation

The anisotropic Janus membrane with double side-opposite wettability shows a great potential for switchable emulsion separation, but it remains a challenge to construct a Janus membrane with good mechanical stability, extremely asymmetric wettability, and excellent anti-fouling performance. In this study, a novel Janus copper mesh membrane with extremely asymmetric wettability was rationally constructed for water unidirectional permeation and emulsion separation. The superhydrophilic CuO nanosheets lower skin layer of the novel Janus membrane was fabricated by the chemical oxidation method, while the superhydrophobic γ-Fe2O3@PVDF upper skin layer was deposited on the CuO-coated mesh surface by elaborately tuning the transient state of the electrospraying and electrospinning. The as-prepared Janus membrane exhibited a tightly interlocking structure with extremely asymmetric wettability and delivered water unidirectional permeation and efficient separation of both oil-in-water and water-in-oil emulsions. After separation with such Janus membrane, the residual oil contents in the filtrates after oil-in-water emulsion separation were all less than 50 mg/L, and the residual water contents in the filtrates after water-in-oil emulsion separation were lower than 150 mg/L. The Janus membrane was further demonstrated desirable anti-fouling ability and superior recycle stability. Therefore, this novel Janus membrane may be potentially used as a next-generation membrane for a broad field-scale application in smart oil/water separation.