Constructing re-entrant superhydrophobic structures on membrane surface for robust anti-wetting membrane distillation

Abstract

The practical application of membrane distillation (MD) remains limited by membrane wetting and scaling, particularly in the presence of low surface tension contaminants and inorganic scalants. The traditional fluorination modification method of hydrophobic membrane surface fluorination only realizes the chemical modification and then improves the anti-wetting and anti-scaling performances, but it is difficult to maximize the effect by constructing the secondary structure of fluorinated material. In this study, we introduce an interfacial phase separation method to create pure fluoropolymer (AF2400) structure on the surface of hierarchical polyvinylidene fluoride (PVDF) membranes. The optimal AF2400 layer features thin and porous structure generating a secondary re-entrant. The modified membranes exhibited enhanced resistance to both wetting and scaling, maintaining stable MD operation for 16 h with a 0.6 mM sodium dodecyl sulfate (SDS) solution as feed and for 30 h with a mixed foulant feed solution containing 0.2 mM SDS and 20 mM gypsum. The synergistic effect of hierarchical morphology and engineered surface chemistry contributed to improved membrane robustness and long-term performance. These results highlight a scalable and effective approach to fabricating advanced MD membranes with robust anti-wetting and anti-scaling performance.