Sustainable recycling of waste poly(vinylidene fluoride) and rational design of Janus membrane with superhydrophilic/hydrophobic asymmetric wettability for efficient separation of surfactant-stabilized water-in-oil and oil-in-water emulsions

Membrane materials are great interest in the purification of oily wastewater due to their special wetting and high selectivity, however, the membrane fouling, poor recyclability and inferior efficiency significantly restrain the practical application. Herein, waste cellulose is used as the membrane matrix and modified with dopamine to obtain a super-hydrophilic polydopamine/cellulose membrane (PDA/CM). Secondly, poly(vinylidene fluoride) (PVDF) fiber membrane was electrospun on the surface of super-hydrophilic PDA/CM to form hydrophobic PVDF, and finally a Janus membrane (PVDF/PDA/CM) with asymmetric wetting properties was obtained for the separation of water-in-oil and oil-in-water emulsions. The structure, emulsion separation performance and mechanical properties of Janus membrane were discussed. The PDA/CM membrane side exhibits suphydrophilicity, which can separate various oil-in-water emulsions with efficiency of above 99%. Oppositely, the PVDF side owns hydrophobicity, which can separate various water-in-oil with efficiency of above 98.8%. After 10 cycles, the separation permeation flux remained over 14,000 L m-2 h-1 bar- 1 for oil -in -water emulsions and 8000 L m- 2 h-1 bar -1 for water -in -oil emulsions, demonstrating its good recycling ability. This work can provide a new strategy for designing laminated Janus separation membrane and realize the on -demand separation of surfactantstabilized water -in -oil emulsions and oil -in -water emulsions by inversion of the membrane.