Omniphobic palygorskite coated Janus membrane with enhanced fouling and wetting resistance for direct contact membrane distillation

Abstract

Abstract A novel omniphobic-hydrophilic Janus membrane was developed to tackle the problems of traditional hydrophobic membrane wetting and fouling during membrane distillation (MD). The asymmetric membrane was first fabricated by simply depositing dopamine (DA) on a commercial polytetrafluoroethylene/polyethylene terephthalate (PTFE/PET) membrane. The low-surface-energy omniphobic surface with multilevel re-entrant structures was developed via spraying cylindrical palygorskite (PAL) nanorods, which were modified by polydopamine (PDA) coatings and fluorinated by 1H, 1H, 2H, 2H-perfluorodecyltriethoxysilane (17FAS). The asymmetric Janus membrane possessed outstanding wettability: the top layer achieved omniphobic (163.9°) while the bottom layer displayed underwater superoleophobicity (157.2°). In direct contact membrane distillation (DCMD) operations, the Janus membrane exhibited a robust desalination performance (salt rejection of ~100%) and excellent stability (over 50\xa0h) while treating different types of surfactant-stabilized mineral oil-in-water emulsions, demonstrating the superior wetting and fouling resistance of the membrane. Overall, the results exemplified an effective strategy for engineering Janus membranes with an omniphobic PAL and a hydrophilic PDA layer. Importantly, the Janus membrane shows broad application prospects in the field of MD processes for water recovery from industrial wastewater containing complex compounds.