Ultra-permeable thin-film nanocomposite membrane with an asymmetric structure harvested by a heterogeneous interlayer for brackish water desalination

Abstract

Constructing interlayers has proven highly efficacious in augmenting the performance of polyamide (PA) NF membranes. However, the fabrication of highly-permeable interlayered RO membranes poses significant challenges. In this work, we propose a hydrophilic-hydrophobic heterogeneous interlayer strategy to fabricate an ultra-permeable thin-film nanocomposite membrane with asymmetric two-layered structures (a-TFN). This membrane comprises a dense PA upper layer doped with ordered ZIF-8 nanocrystals and a porous dendrimer lower layer. The heterogeneous interlayer, characterized by nonuniform wettability, is more supportive of the eruption and diffusion of MPD monomers compared to a hydrophilic interlayer, beneficial to the formation of a highly cross-linked PA layer replete with nanovoids. Additionally, the in-situ encapsulation of ZIF-8 nanocrystals within the dense PA layer provide additional transport channels, while the dendrimer layer serves as a gutter layer, collectively enhancing water transport. The resulting a-TFN membrane exhibits an unprecedented water permeance (8.67 ± 0.13 L·m−2·h−1·bar−1), outperforming state-of-the-art commercial and advanced structural RO membranes, while maintaining competitive NaCl rejection (98.1 ± 0.19 %). Furthermore, it demonstrates exceptional structural durability, resistance to compaction, and antifouling performance. This study provides valuable insights for the design of interlayered RO membranes with enhanced performance.