Imidazole-based I-quartet-incorporated polyamide nanofiltration membranes with enhanced perm-selectivity

Polyamide (PA) membranes prepared via interfacial polymerization have been widely used for nanofiltration (NF) processes for which breaking the permeability/selectivity trade-off remains a key challenge. Lower performances are obtained from thick or defect polyamide layers, largely due to the rapid reaction of monomers during interfacial polymerization. In this study, functional additives, bis-hexylureido-imidazole (DC6) and bis-octylureido-imidazole (DC8), were mixed with the aqueous phase containing piperazine (PIP) to regulate the interfacial polymerization reaction and indirectly enhance water permeation behaviors. DC8 could form a self-assembled tetrameric I-quartet superstructure in the aqueous phase, which slows down PIP diffusion towards the oil-water interface, promoting the formation of a thinner, and more uniform PA layer. Density functional theory (DFT) and molecular dynamics (MD) simulations were further used to confirm the above findings. The optimized membrane exhibited excellent rejection of both Na 2 SO 4 (96.2 %) and MgCl 2 (93.7 %), ∼ 50% increased water permeability from 16.5 L·m -2 ·h -1 ·bar -1 up to 24.4 L·m -2 ·h -1 ·bar -1 and high (SO 4 2- /Cl - = 28.9, Mg 2+ /Na + = 13.0 selectivity) during 60 hours stable evaluation with mixed salts. The study offers a new strategy for regulating interfacial polymerization via self-assembled imidazole I-quartets and expands the application of such supramolecular assemblies in designing high-performance membranes for efficient nanofiltration.