Hydrogel modified evaporation interface for highly stable membrane distillation

Abstract: Surface effect of low-surface-tension contaminants accumulating at the evaporation surface can easily induce membrane wetting in the application of membrane distillation, especially in hypersaline scenarios. In this work, we propose a novel strategy to eliminate the surface effect and redistribute contaminants at the evaporation interface with simply incorporating a layer of hydrogel. The as-fabricated composite membrane exhibits remarkable stability, even when exposed to extreme conditions, such as a salt concentration of 5M and surfactant concentration of 8 mM. The breakthrough pressure of the membrane is as high as 20 bars in the presence of surfactants, surpassing commercial hydrophobic membranes by one to two magnitudes. Combined study of density functional theory and molecular dynamics simulations reveals the important role of hydrogel-surfactant interaction in suppressing the surface effect. As a proof of concept, we also demonstrate the stable performance of the membrane in processing synthetic wastewater containing surfactants of 144 mg L-1, mineral oils of 1g L-1 and NaCl of 192 g L-1, showing potential of the membrane in addressing challenges of hypersaline water treatment and zero liquid discharge processes.