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

•Janus membranes are fabricated by single-sided PDA/PEI deposition on PP hollow fibers.•Thickness of the hydrophilic layer can be facilely adjusted by the deposition time.•The Janus membranes exhibit up to 120% improvement in the water flux for DCMD.•Good operational stability and high salt rejection are obtained with Janus membranes.