Polyamide membrane based on hydrophilic intermediate layer for simultaneous wetting and fouling resistance in membrane distillation

Thermally driven membrane distillation (MD) has garnered significant attention in hypersaline solution treatment. However, MD membranes suffer from inevitable membrane fouling and wetting owing to its inherent hydrophobicity and the complex composition of wastewater. Herein, dense polyamide (PA) Janus membranes based on both polyvinyl alcohol (PVA) and aramid nanofiber (ANF) intermediate layers are fabricated atop the hydrophobic polytetrafluoroethylene (PTFE) substrate via a coating-assisted interfacial polymerization (IP) method. The PVA and ANF hydrophilic coatings provide a favorable interface condition for the IP process to facilitate the introduction of a complete and dense PA layer. While treating the oily saline feed, both PA Janus membranes can significantly resist fouling owing to hydrophilic PA composite layers. When treating saline feed containing a high sodium dodecyl sulfate (SDS) surfactant, the PA/PVA PTFE membrane might experience progressive wetting with a prolonged operation time caused by SDS penetrating through the PA/PVA composite layer, while the PA/ANF PTFE membrane exhibits robust wetting resistance. Benefiting from ANF coating with superior swelling resistance and thermal stability conducive to maintain a denser and more complete PA layer compare to PVA coating, the PA/ANF PTFE membrane simultaneously resists wetting and fouling when dealing with a complex saline solution containing both oil and SDS surfactant, which is confirmed by its stable flux and low permeate conductivity in the continuous MD operation for 100 h. Scalable fabrication process and robust performance of the composite membrane endow it with great potential in saline wastewater desalination practicability.