Amphiphobic surface modification of electrospun nanofibrous membranes for anti-wetting performance in membrane distillation

Membrane distillation (MD) works as a promising alternative of RO to desalinate hypersaline water owing to its unique advantages including high concentration brine tolerance, 100% theoretical solute rejection, and low operating pressure. Hydrophobic MD membranes face critical challenge to treat industrial wastewaters containing low surface tension substances because these substances led to membrane wetting with loss of membrane permeability and rejection. In this study, we report a simple and facile approach to fabricate amphiphobic polyvinylidene fluoride-co-hexafluoropropylene (PVDF-HFP) electrospun nanofibrous membranes with anti wetting property. 1H,1H,2H,2H-perfluorodecyltriethoxysilane (FAS) was used to fluorinate PVDF-HFP fibers and was then crosslinked to form a network upon dealcoholization under thermal treatment. The FAS-coated PVDF-HFP nanofibrous membranes exhibited great stable amphiphobicity with high contact angles against both water and oil, even challenged under critical conditions including boiling water, and strong base and acid etchings. Surface fluorination of PVDF-HFP nanofibrous membrane with the FAS coating did not sacrifice its permeate flux and salt rejection much. The fabricated amphiphobic nanofibrous membrane exhibited robust MD performance in the long-term operation and also in the presence of surfactant sodium dodecyl sulfate in the feed saline solution.