Using piezoelectric mechanochemistry for solvent-free, nonthermal defluorination of perfluoroalkyl substances (PFAS) contained in carbon-based sorbents

Abstract

Mechanochemical methods such as ball milling offer a solvent-free and non-thermal approach for PFAS remediation, enabling not just separation but actual destruction of PFAS through defluorination. In this study, we demonstrate that effective PFAS defluorination using ball milling critically depends on the presence of a co-milling catalyst, in this case piezoelectric catalysts such as boron nitride (BN), which showed the highest performance among other tested piezoelectric materials. While BN has already proven effective for defluorination of pure PFAS compounds, PFAS in sediments, and aqueous film-forming foam (AFFF), prior studies have been limited by the small amounts of PFAS they can treat inside another medium. To overcome these limitations, we present as an alternative the coupling of BN with activated carbon as a pre-concentration medium for PFAS. By leveraging activated carbon's high sorption capacity, we were able to destroy nearly 100 times higher mass of PFOA in less than one-third of the time compared to previous studies on sediments or AFFF. These results suggest that the design of larger-scale ball milling systems for PFAS destruction should incorporate the use of high-capacity sorbents to concentrate contaminants, thus destroying higher amounts more effectively. While in the case of activated carbon the chances of reusing it after milling are minimal, it could be safely disposed of without the risk of releasing PFAS back into the environment.