Omniphobic PVDF nanofibrous membrane for superior anti-wetting performance in direct contact membrane distillation

Membrane wetting caused by low surface tension pollutants in feed solution has been a major challenge for membrane distillation (MD), and omniphobic membranes have been proposed as a promising solution to address this challenge due to their strong repellence towards liquids with a broad range of surface tensions. In this study, we report a nanoparticle-free strategy to fabricate omniphobic polyvinylidene fluoride (PVDF) nanofibrous membranes for robust MD desalination. A solvent-thermal induced roughening method was used to create multiscale hierarchical nanofin structures on electrospun PVDF nanofibers, followed by a polydopamine-anchored surface fluorination treatment to reduce the surface energy of the nanofibrous membrane. We show that the as-prepared membrane exhibited super repellence (>150°) to diverse liquids with surface tension ranging from 73 to 30 mN m⁻¹. Moreover, the omniphobic membrane maintained stable salt rejection and water flux in direct contact MD processes in the presence of sodium dodecyl sulfate surfactant (up to 0.4 mM) or mineral oil (up to 480 mg L⁻¹), demonstrating its promising potential in practical water reclamation from MD applications.