Structural tailoring of hierarchical fibrous composite membranes to balance mass transfer and heat transfer for state-of-the-art desalination performance in membrane distillation

Abstract

Membrane distillation (MD) displays superior characteristics to other technologies to alleviate the ever-increasing freshwater crisis through seawater desalination and/or wastewater recycling. However, the critical challenge in MD is fabricating high-performance membranes. In this study, we fabricated a high-performance hierarchical fibrous composite (HFC) membrane to acquire a high water flux while maintaining a high salt rejection for MD. This HFC membrane comprises of a thin active dense layer with small poly (vinylidene fluoride-co-hexafluoropropylene) (PH) nanofibers to allow maximum mass transfer and a thick support layer with large poly(ethylene terephthalate) (PET) microfibers to give minimum heat transfer. By tailoring the structures of both the active and support layers to reduce the trade-off between the mass transfer and heat transfer during the MD process, the optimized HFC membrane, having a 3 μm thick PH active layer and 70 μm thick PET support layer, achieved the highest reported water flux of 79.21 ± 4.17 L m⁻² h⁻¹ and the salt rejection was higher than 99.9% using 3.5 wt% NaCl as the feed under a temperature difference of 40 °C in direct contact membrane distillation (DCMD). Our study describes a novel HFC membrane which demonstrates great achievements in elevating the MD performance.