Minimize the trade-off between wetting resistance and water permeance in membrane distillation with ion-sieving coating layer

Abstract

• An ion-sieving layer was introduced into the MD system for anti-wetting. • Swelling of ion-sieving layer was mitigated by intercalating Ca 2+ ions. • The trade-off between wetting resistance and water permeance was overcome. • Mass transport in janus, omniphobic and ion-sieving membrane was discussed. The conventional hydrophobic membranes in membrane distillation system are prone to be wetted by surfactants. Meanwhile, there is a trade-off between wetting resistance and water permeance on advanced membrane materials, such as Janus membrane and omniphobic membrane. To overcome this dilemma, a composite membrane with ion-sieving layer was fabricated by self-assembling MXene nanosheets on the commercial PTFE membrane. The coating layer exhibited ordered subnanometer channels, and the stability can be further enhanced by intercalating Ca 2+ ions between the two-dimensional MXene pieces. The experiments using SDS-NaCl solution and realistic wastewater demonstrated that such modification can provide an excellent anti-wetting property without sacrificing the permeate flux. The anti-wetting property can be attributed to the ion-sieving effect, which created an energy barrier by the partial dehydration of ions. Simultaneously, the ion-sieving layer has a much lower water transfer resistance than the coating layer on conventional Janus membrane due to its ordered nanostructure, and the hydrophobic substrate can provide a larger effective evaporation interface compared with the omniphobic membrane. This article attempts to provide an insight into the novel membrane distillation system coupled with ion-sieving effect, and paves the way for developing advanced membranes for treating wastewater with low surface tension contaminants.