Constructing superhydrophilic/superhydrophobic Janus membrane assisted by dual-interface-confined strategy for on-demand oil-in-water and water-in-oil emulsions separation

A Janus membrane with asymmetric superwettability on opposite surface for efficient on-demand oil-in-water and water-in-water emulsions separation. [Display omitted] •A dual-interface-confined strategy for preparing a stable Janus membrane with asymmetric superwettability.•Featured both superhydrophilicity/underwater superoleophobicity and superhydrophobic/superoleophilicity.•Achieving both water-in-oil and oil-in-water emulsions separation by simple reversing the membrane.•Promotion long-term on-demand oil/water emulsion separation without significant performance decline. Janus membranes with asymmetric wettability have attracted much attention because they can solve the problem that a single wettable material cannot effectively separate complex oil/water emulsions. Here, a dual-interface-confined strategy combining single-side interface-confined floating and single-side interface-confined spraying methods is provided to fabricate a robust Janus membrane with superwettability. The controllable single-side interface-confined floating method introduces a superior stable hydrophobic-superhydrophilic Janus interface, and the single-side interface-confined spraying method guarantees a robust superhydrophobic-superhydrophilic Janus interface. The Janus membrane featured both superhydrophilicity and superhydrophobicity with the outstanding stable interface and remarkable chemical stability could separate not only surfactant-stabilized water-in-oil emulsions by gravity alone, but also handle the surfactant-stabilized oil-in-water emulsions under low separation pressure through simple operation process. Moreover, this superwettable Janus membrane can achieve long-term on-demand oil/water emulsion separation with low flux decline and near 100% flux recovery. Overall, this work develops a new avenue for Janus membrane and provides a new application for a variety of oily wastewater treatment problems.