Janus membranes with asymmetric wettability via a layer-by-layer coating strategy for robust membrane distillation

Abstract

Commercial membranes for membrane distillation experience severe wetting and fouling phenomena, which largely hinder their practical applications. To address these issues, a novel strategy to fabricate the Janus membrane is proposed via a facile layer-by-layer coating of Teflon® AF1600 and polydopamine (PDA) on an oxygen plasma treated commercial polytetrafluoroethylene/polypropylene (PTFE/PP) membrane. The resultant membrane has a unique asymmetric surface wettability. In brief, the top layer of the Janus membrane is strongly hydrophobic (145.1 ± 1.8°), while the bottom layer exhibits underwater superoleophobicity (154.2 ± 2.2°) and in-air hydrophilicity (33.5 ± 1.2°). As a result, the Janus membrane possesses a significantly enhanced wetting resistance toward common liquids including pure water, surfactant, ethanol, and crude oil, compared to the unmodified membrane. Due to the excellent anti-fouling property, the Janus membrane also shows a rather robust desalination performance (i.e., a slight decline in water flux and negligible salt passage) when treating a multi-component saline wastewater containing both humic acid and crude oil, ending up with a high water recovery ratio of 50%. Overall, the Janus membrane developed in this work is highly promising for the water reclamation from highly saline wastewater containing complex organic compounds.