Nanovehicle-assisted monomer shuttling enables highly permeable and selective nanofiltration membranes for water purification

Abstract

Fabricating nanofiltration membranes with high water permeance and selectivity is crucial to efficient water purification. However, achieving such a goal with a simple and cost-effective approach that is compatible with existing membrane manufacturing infrastructure remains a substantial technical challenge. Here we show a strategy of nanoemulsion-regulated interfacial polymerization (NERIP) based on nanovehicle-assisted monomer shuttling for fabricating highly permeable and selective nanofiltration membranes. In NERIP, the nanovehicles, which are surfactant-stabilized oil droplets (in water) enriched with piperazine (PIP), enter and merge into the hexane phase to initiate the polymerization between PIP and trimesoyl chloride. This nanovehicle-assisted monomer shuttling results in the formation of polyamide ‘bubbles’ that later collapse into nanocraters. The nanocrater structure substantially increases the surface area and void fraction of the polyamide layer. The PIP shuttling also accelerates the polymerization reaction, enabling the formation of a thin and highly cross-linked polyamide layer with a more uniform pore size distribution. These structural superiorities yield an unprecedentedly high performance with a water permeance of 36.8 ± 1.9 l m−2 h−1 bar−1 and a Na2SO4 rejection of 99.6 ± 0.1%. NERIP creates a new dimension to fabricate highly permeable and selective nanofiltration membranes for desalination and water purification. The development of advanced nanofiltration membranes should be compatible with existing manufacturing process to be practically useful. A process based on nanoemulsion-regulated interfacial polymerization allows the fabrication of low-cost and high-performance membranes.