<i>In Situ</i> Surfactant-Assisted Assembly for Efficient Removal of PFAS by Low-Pressure Ultrafiltration Membrane Process

The widespread use of perfluoroalkyl and polyfluoroalkyl substances (PFAS) has raised serious environmental and public health concerns, driving the urgent need for effective and scalable removal technologies. In this study, we present a surfactant-assisted ultrafiltration (UF) strategy for enhanced PFAS separation through leveraging <i>in situ</i> assembly of PFAS molecules with the cationic surfactant cetyltrimethylammonium bromide (CTAB). The addition of CTAB (0.14 mM) induces the formation of nanoscale complexes or micelles with PFAS, thus promoting their effective retention by UF membranes (99.1% for 0.14 mM CTAB vs 30.3% without CTAB). Moreover, both experimental and modeling results reveal a concentration polarization effect that leads to the accumulation of CTAB on the membrane surface. As such, even when the bulk concentration of CTAB is below its critical micelle concentration, localized micelle formation occurs near the membrane interface, enabling effective retention of PFAS. Notably, the CTAB-enhanced UF process is also effective in retaining other PFAS species, especially long-chain compounds such as PFHxA. Further experiments indicate that compared with electrostatic interactions, hydrophobic interactions between PFOA and CTAB play a more dominant role in forming micelles, thereby governing the subsequent retention by UF membranes. This study offers mechanistic insights into surfactant-mediated PFAS removal and presents a scalable, low-pressure membrane strategy for the effective treatment of PFAS-contaminated water.