Ionic liquids tailored ultra-permeable antifouling nanofiltration membranes for water purification

Nanofiltration (NF) exhibits significant promise in tackling the worldwide water crisis, and the endeavor to develop high-performance NF membranes constitutes an essential long-term goal. In this study, an ionic liquid, [tetrakis(hydroxymethyl) phosphonium chloride, THPC], was employed as structural modifiers to prepare NF membranes. Hydrogen bonding effects between the hydroxyl group in THPC and the amino group in piperazine (PIP) decelerated the diffusion rate of PIP, which is verified by molecular dynamic simulations. This, together with the spatial effect provided by the unique tetrahedral structure of THPC, allowed to form a thinner, smoother, looser, and more hydrophilic polyamide selective layer. The resultant NF membrane achieved an ultra-high permeance (43.2 L m−2 h−1 bar−1) with satisfactory Na2SO4 rejection (97.8%), and a significant enhancement in its antifouling performance. Our work has achieved simultaneous optimization of NF membrane permeation-selectivity and antifouling performance through simple and cost-effective measures, which will inspire the construction of the coming version of high-performance NF membranes.