Rapid Degradation and Mineralization of Perfluorooctanoic Acid by a New Petitjeanite Bi3O(OH)(PO4)2 Microparticle Ultraviolet Photocatalyst

Water treatment techniques for destructive removal of perfluoroalkyl substances (PFAS) have only recently begun to emerge in the research literature, comprising unconventional advanced oxidation and reduction methods. Photocatalytic degradation of PFAS has not been widely pursued, which is a result of the limited ability of common semiconductor materials to induce C–F bond cleavage in aqueous systems. Herein, degradation of perfluorooctanoic acid (PFOA) by bismuth phosphate photocatalysts under ultraviolet irradiation has been investigated for the first time, including the relatively well-known monoclinic BiPO4 wide band gap semiconductor, as well as a novel Bi3O(OH)(PO4)2 (BOHP) composition. Compared to BiPO4 and a β-Ga2O3 nanomaterial reference catalyst, BOHP microparticles achieved dramatically faster PFOA degradation and mineralization, despite both a smaller surface area and a lower band gap energy. The rate constant for degradation of PFOA by BOHP in a pure water solution was ∼15 times greater than those of both BiPO4 and β-Ga2O3 (∼20–30 times greater when normalized for surface area) and was on the same order of magnitude as that of phenol degradation by P25 TiO2 in the same photoreactor. The superior performance of BOHP was primarily related to the surface charge and adsorption behavior of PFOA, in combination with the favorable redox potentials of BOHP charge carriers. The catalyst was further tested at low PFOA concentrations (i.e., microgram per liter range) in the presence of natural organic matter, and rapid degradation of PFOA was also observed, indicating the potential of BOHP to enable practical ex situ destructive treatment of PFAS-contaminated groundwater.