Nanofibrous Janus membrane with improved self-cleaning property for efficient oil-in-water and water-in-oil emulsions separation

Developing a membrane integrating high separation efficiency and good anti-fouling ability for both oil-in-water and water-in-oil emulsions is meaningful due to the complexity and diversity of actual oily wastewater. Herein, a facile strategy was designed to generate a nanofibrous Janus membrane to achieve multifunctional and self-cleaning properties. Hydrophilic β-FeOOH was anchored on poly(vinylidene fluoride-co-hexa-fluoropropylene) (PVDF-HEP) fibers to achieve hydrophilicity and self-cleaning performance of PVDF-HEP/β-FeOOH layer by in situ mineralization technology. The Janus membrane was then obtained by incorporating PVDF-HEP fibers layer onto the hydrophilic layer through electrospinning technology. PVDF-HEP/β-FeOOH layer owns superhydrophilicity (WCA = 0°) and underwater superoleophobicity (OCA = 159°), which can separate different surfactant-stabilized oil-in-water emulsions with separation efficiency of above 99.8 % when this layer is facing up. Conversely, the PVDF-HEP layer exhibits superhydrophobicity (WCA = 149°), which can separate different surfactant-stabilized water-in-oil emulsions with separation efficiency of above 99 % when this layer is facing up. More importantly, a satisfying water flux recovery rate of 98.2 % is acquired due to the synergistic effect between β-FeOOH photocatalysis and asymmetric wettability of the membrane, endowing the membrane with effective self-cleaning capability and satisfactory stability. This study provides a new strategy for designing multifunctional membrane toward actual complex oily wastewater treatment.