Synergy of super-liquid-repellency and nanoscale sieving in a sandwich-architectured janus membrane for stable membrane distillation of hypersaline wastewater.

Membrane distillation (MD) remains plagued by membrane scaling, wetting, and a persistent permeability-selectivity trade-off often intensified by conventional surface modifications. Herein, we propose a rational dual-barrier design strategy to construct a sandwich-structured Janus membrane (termed as #PVDF-NA) via sequential functionalization of a polyvinylidene fluoride (PVDF) substrate. This hierarchical architecture integrates a super-liquid-repellent polysiloxane nanofilament (PN) top layer, self-assembled from hydrolyzed trichloromethylsilane, with an underlying dense polyamide (PA) network formed through interfacial polymerization between trimesoyl chloride and m-phenylenediamine. The #PVDF-NA membrane achieved a permeate flux of 34.6 kg·m⁻²·h⁻¹, comparable to that of the original #PVDF membrane (33.7 kg·m⁻²·h⁻¹) while maintaining excellent salt selectivity. This exceptional performance stems from an unconventional vapor transport mechanism that couples polyamide matrix dissolution-diffusion with pore-flow permeation. Under harsh MD conditions using 20 wt% NaCl and 25 mM gypsum feeds, #PVDF-NA demonstrated unprecedented anti-scaling capability, evidenced by stable permselectivity over an extended duration. When challenged with surfactant and ethanol-containing feeds, the membrane exhibited delayed wetting onset and preserved structural integrity despite gradual flux decline. Notably, partial wetting did not compromise water quality, ensuring continuous production of high-purity permeate. These superior attributes arise from the synergistic interplay between the extreme liquid repellency of the PN top layer and the precise molecular sieving of the PA barrier. Long-term desalination of real seawater (∼50 h) further verified the remarkable operational stability of #PVDF-NA. This work introduces an advanced Janus membrane architecture and a versatile platform for energy-efficient MD, offering a robust and practical pathway toward sustainable treatment of hypersaline wastewater.