Surface Functionalization of Mxene for Enhanced and Rapid Removal of PFOS and Pfbs from Water

Per- and polyfluoroalkyl substances (PFAS) are synthetic chemicals that do not degrade easily in the environment. Once released into water, they persist for long periods, accumulate in living organisms, and pose serious health risks. This persistence arises from their strong C–F bonds and carboxylic or sulphonyl groups, which make them both water-loving and oil-resistant. These properties give PFAS exceptional stability, heat resistance, and strong surface activity. Consequently, PFAS such as perfluorobutanesulfonic acid (PFBS) and perfluorooctane sulfonate (PFOS) have been widely used in products like stain-resistant fabrics and firefighting foams, leading to their widespread release into aquatic systems. The U.S. Environmental Protection Agency (USEPA) has set extremely low safe limits for PFBS (10 ppt) and PFOS (4 ppt). Several methods, including adsorption, thermal degradation, and membrane filtration, have been explored for PFOS and PFBS removal, but none are fully effective. Adsorption, while promising, often suffers from slow kinetics, weak binding to short-chain PFAS, and reduced efficiency in the presence of competing ions. This highlights the urgent need for faster, more selective, and cost-effective solutions.

In this work, we investigated MXene (Ti₃C₂Tₓ), a two-dimensional nanomaterial with surface groups (–O, –OH, –F) suitable for modification. We synthesized two variants: amine-functionalized MXene (NH₂-MXene) and fluoride-functionalized MXene (F-MXene). These modifications altered the surface charge: pristine MXene was negatively charged (−30 mV), whereas NH₂-MXene (+42 mV) and F-MXene (+4.97 mV) became positively charged at pH 5. Adsorption studies showed that NH₂-MXene and F-MXene removed PFOS and PFBS much faster than unmodified MXene. The amine groups enhanced removal through electrostatic attraction (+NH₃⁺ of MXene with SO₃⁻ of PFOS and PFBS), while the fluoride groups promoted fluorophilic C–F···F–C interactions. This dual mechanism significantly enhanced performance. To test under realistic conditions, we also used tap water spiked with PFOS and PFBS, and the functionalized MXenes proved highly effective.

Overall, these findings demonstrate that surface-modified MXenes can selectively and rapidly capture PFOS and PFBS, making them promising candidates for cost-effective water treatment technologies to achieve PFAS-free drinking water.