Janus hollow fiber membrane with a mussel-inspired coating on the lumen surface for direct contact membrane distillation

Membrane distillation is a thermally driven separation process that is widely applied in desalination and wastewater treatment. Hydrophobic membranes with high mass transfer and low heat transfer are desirable in conventional direct contact membrane distillation (DCMD). In this work, we reported a facile method to fabricate Janus hollow fiber membranes with asymmetric wettability for DCMD. The hydrophilic polydopamine/polyethyleneimine coating was deposited onto the lumen surface of hydrophobic polypropylene hollow fiber membrane, and the hydrophilic layer thickness could be easily adjusted by the deposition time. During the DCMD test, the Janus membrane showed an improved permeate flux with the increasing deposition time and operation temperature, and the flux improvement was up to 120% for the Janus membrane deposited for 6 h with 80 °C feed. On the other hand, the Janus membrane also exhibited a high salt rejection and good long-term stability in saline feed desalination with a deposition time of 2 or 4 h. Moreover, this research provides us a facile method to fabricate Janus membranes for other applications.