Resorcin[4]arene-derived hierarchical porous organic polymer modulated polyamide TFC membrane for effective ion separation

Abstract

Fine-customized structure and morphology of the thin-film-composite polyamide membranes (TFC-PA) play an essential role in obtaining high water permeance and solute–solute selectivity. Herein we fabricated a TFC-PA nanofiltration membrane with excellent separation performance by the regulation of the interfacial polymerization process via a resorcin[4]arene-derived hierarchical POPs intermediate layer (RA-POPs). The RA-POPs interlayer was constructed on the PSF substrate surface through in situ covalent assembly by the azo-coupling reaction, followed by the formation of the PA layer on top of this porous layer. The effect of azo-coupling reaction conditions on the morphologies and performance of the prepared TFC-PA-POPs membranes was investigated. The constructed RA-POPs layer interlayer increased the hydrophilicity of the substrates. This hydrophilic RA-POPs interlayer facilitated the uniform distribution of the amine solution and slowed down the PIP diffusion into the organic phase by the supramolecular interactions. Consequently, the formed PA layer exhibited a thinner thickness, a high degree of crosslinking, a crumpled structure and an enhanced negatively charged surface. The obtained TFC-PA-POPs membranes possessed high water permeance of 21.0 L m⁻² h⁻¹ bar⁻¹, comparable Na₂SO₄ rejection of 99.35 % and excellent mixed ion selectivity (Cl⁻/SO₄²⁻) of 340 in the high salt concentration, which is superior to the commercial and the state-of-the-art polyamide-based NF membranes. The reduced pore size, narrowed pore size distribution and enhanced surface negative charge endowed the TFC-PA-POPs membranes with high mono/multivalent anions selectivity. Our approach for modulating the polyamide microstructure by incorporating macrocycle-derived hierarchical porous organic polymer interlayer has provided insight into the design of TFC-PA NF membranes with high water permeance and precise ion separation for high-salinity wastewater treatment and water purification.