Photocatalytic Degradation of PFAS Under Field Water Matrix Conditions Using an Adsorptive Photocatalyst

Abstract

Per- and polyfluoroalkyl substances (PFAS) are ubiquitous in surface waters. While numerous technologies have been investigated to mitigate human exposure, limited information is available for treatment of PFAS in actual field waters. Based on the “concentrate-and-destroy” strategy, we prepared and evaluated an adsorptive photocatalyst, namely gallium-doped activated carbon-supported titanate nanotubes (Ga/TNTs@AC), for treatment of six PFAS in a model surface water. Being most prevalent in the field water, perfluorooctane sulfonate (PFOS) was selected as a representative compound for feasibility and optimization studies. Batch experiments revealed that at a dosage of 1 g/L, Ga/TNTs@AC adsorbed 98% of 100 µg/L PFOS in the surface water within 10 min. Background cations enhanced PFOS removal by suppressing repulsive forces and enabling the cation-bridging effects. Upon UV irradiation, 35.5% of adsorbed PFOS was effectively degraded and 25.8% defluorinated. The photocatalytic defluorination of PFOS was boosted to 70.0% by addition of 60 µM Fe³⁺ during the photodegradation, where formation of Fe³⁺-PFOS and Fe³⁺-DOM complexes reduced the energy barrier, facilitated activation of PFOS, and diminished inhibitory effects of DOM. Acidic conditions were found favorable for both adsorption and photocatalysis of PFOS. Fixed-bed column tests confirmed the effective adsorption of PFOS and other PFAS in the field water, with complete PFOS breakthrough occurred after 5100 bed volumes. Subsequently, the PFAS-laden Ga/TNTs@AC successfully degraded the pre-concentrated PFAS, which also regenerated the Ga/TNTs@AC media for reuse. Ga/TNTs@AC appeared to be a promising material for enabling the “concentrate-&-destroy” strategy for more efficient removal and degradation of PFAS in field waters.