Customizing membrane microstructures for targeted removal of per- and polyfluoroalkyl substances for healthy drinking water

Efficient removal the hazardous per - and polyfluoroalkyl substances (PFAS) is imperative for healthy drinking water. The scalable and cost-effective nanofiltration (NF) process is considered the golden option for removing PFAS, but the inherent membrane structural properties usually induce unsatisfactory removals as well as low permeance. To overcome this challenge, we used the polar solvent ethanol (ETOH) as a co-solvent for the interfacial polymerization (IP) process to achieve precise modulation of the microstructural properties of NF membranes. The presence of ETOH enriched the piperazine (PIP) monomers on the organic side of the IP reaction zone, contributing to enhanced local reaction heat release and the formation of nanobubbles. Thus, a denser and less intruded substrate with a more homogeneous distribution of the nanobubble structure of the polyamide layer was achieved. Advantageously to the structural features, the preferred ETOH-4 NF membranes exhibited excellent permeability (17.54 LMH/bar) and selectivity (1821.45 bar^-1 for water/Na₂SO₄ and 180.67 bar^-1 for NaCl/Na₂SO₄). The ETOH-4 membrane demonstrates exceptional efficacy in the removal of 22 PFAS compounds, achieving removal rates ranging from 93.42 % to 99.99 %. Furthermore, it exhibits remarkable selectivity between water and PFAS substances. An in-depth analysis showed that the enhanced size exclusions were the main reason for the efficient removal of PFAS. This work provides a new route for customizing the microstructures of high-performance NF membranes for efficient PFAS removals.