Enhanced hardness removal by polyamide thin-film composite nanofiltration membranes modified with a novel P204 based ionic liquid

Hard water softening by removing multivalent cations such as calcium (Ca 2+ ) and magnesium (Mg 2+ ) remain challenging for nanofiltration (NF) membranes due to the trade-off between membrane permeability and selectivity. In this study, chelation ionic liquid ([NH 4 ] [P204]) was synthesized to modify the polyamide selective layer of thin film composite (TFC) NF membranes. This modification enhanced ion rejection of membranes through synergistic effects of size sieving and electrostatic interactions without much compromising the water flux. The optimal membrane NF-ILs-2.0 wt% achieved rejection rates of 95.1 % and 92.5 % for Mg 2+ and Ca 2+ , respectively, alongside a stable water flux of 36.0 LMH. Density functional theory (DFT) calculations and molecular dynamics (MD) simulations revealed the effectiveness of the membranes in removal hardness and strong coordination interactions between [NH 4 ] [P204] and the cations. The novel ionic liquid functions as a promising modifier for-developing advanced NF membranes with enhanced simplicity, efficiency and durability for water treatments.