Supramolecular chemistry assisted construction of ultra-permselective polyamide nanofilm with asymmetric structure for ion sieving

Abstract

Highly-permselective NF membranes are critical to energy-efficient ionic separation. Herein, an ultra-permselective polyamide (PA) nanofilm with asymmetric two-layered structure is achieved by supramolecular chemistry modulated interfacial polymerization (IP) process. Such nearly-40-nm asymmetric PA nanofilm consists of a PA dense layer with nanoscale homogeneity and a polydopamine-β-cyclodextrin (PDA-β-CD) porous layer induced by mussel-inspired surface chemistry, with crosslinking. Experimental characterizations reveal that the exceptionally-hydrophilic and highly-porous PDA-β-CD coating imparts the spatial enrichment and temporal retardation of amine monomers via H-bonding and host-guest interactions, conducing to form the diffusion-difference-enabled striped PA nanofilm with nanoscale ordered structures and enhanced cross-linking degree. Meanwhile, the PDA-β-CD porous coating not only can finely tune the microstructure of PA nanofilm, but also highly prefers for surmounting funnel effect and shortening water transport path. As a result, the resultant asymmetric PA nanofilm attains a noticeable water permeance of 38.59 ± 2.42 L m⁻² h⁻¹ bar⁻¹, competitive retention of Na₂SO₄ (99.4 ± 0.2 %) and unprecedented Cl⁻/SO₄²⁻ selectivity of 202.1, far outperforming the state-of-the-art commercial and lab-made NF membranes. Moreover, it evinces an outstanding ion-sieving performance under the high-salinity solutions, suggesting that our approach for tuning microstructure enables the development of ultra-permeability and excellent selectivity for application in brine refinement and salt reclamation.