A non-substrate-specific technique of antifouling and antiwetting Janus membrane fabrication for membrane distillation

Abstract

Although Janus membranes (comprising a hydrophilic antifouling layer on a wetting-resistant membrane substrate) have shown promise in sustainable membrane distillation (MD) processes for treating industrial wastewaters, most fabrication methods are substrate-specific and lack a universal technique for robust Janus MD membranes. Here, we present a non-substrate-specific technique using polydopamine-assisted, surface-initiated atom-transfer radical-polymerization (ATRP) that grafts a zwitterionic polymer layer onto any wetting-resistant substrate. We first prepare a model omniphobic substrate by surface fluorination of a quartz fiber mat, followed by polydopamine-assisted ATRP to complete Janus membrane fabrication. The grafting of zwitterionic polymer layer with a tunable thickness (∼1–10 μm) on one side of the membrane surface, while preserving the omniphobicity of the membrane substrate, is demonstrated. The binding robustness of the two layers of disparate wettability is then shown. An excellent antifouling functionality of the Janus membrane is confirmed by complete oil detachment in a static oil-fouling test, and by the stable desalination with nearly perfect salt rejection (> 99 %) in direct contact MD using a surfactant-stabilized, crude oil-in-brine emulsion, as simulated high-salinity industrial wastewater feed. Finally, we apply our modification technique to other lab-fabricated as well as commercial non-wetting substrates to demonstrate its universal applicability for Janus membrane fabrication.