An Ultraviolet/Boron Nitride Photocatalytic Process Efficiently Degrades Poly-/Perfluoroalkyl Substances in Complex Water Matrices

Hexagonal boron nitride (hBN) is among several semiconductor photocatalysts shown to degrade poly-/perfluoroalkyl substances (PFAS) in aqueous suspension when excited by ultraviolet-C radiation (UVC; 254 nm); however, only degradation of perfluorooctanoic acid (PFOA) at ppm-range concentrations has been examined in previous reports, showing relatively low efficiency. Herein, photocatalytic treatment of PFOA and other PFAS by hBN was found to be much more efficient than other catalysts when applied to environmentally relevant concentrations in the ppb range. The unexpected inverse concentration dependence is likely related to the contribution of hydrophobic interactions to PFAS adsorption on hBN, as are the observed wider operational pH and salinity ranges. When excited with vacuum ultraviolet-emitting lamps (185/254 nm), hBN was also able to degrade perfluorooctanesulfonate (PFOS) through an unconventional mechanism. Treatment of groundwater contaminated by aqueous film-forming foams was demonstrated in a 5 L hBN+UVC/VUV photoreactor, achieving >99% degradation of PFOA in 15 min and 65% degradation of PFOS in 1 h. Electrical energies per order of destruction for PFOA and PFOS therein were 2.7 and ∼50 kWh•m –3, respectively. The strong performance under a realistic water matrix and operational conditions suggests that hBN photocatalysis warrants further research and consideration as a treatment tool for PFAS contamination.