Per- and polyfluoroalkyl substances (PFAS) have drawn increasing attention due to their omnipresence and adverse health effects. Perfluorooctane sulfonate (PFOS) is one of the most detected PFAS in the aquatic systems. Yet, technologies have been lacking for cost-effectively degrading PFAS in contaminated waters. To address this challenge, we prepared a new adsorptive photocatalyst, Ga/TNTs@AC, based on activated carbon and TiO<sub>2</sub>, and tested the adsorption and subsequent solid-phase photodegradation of PFOS. Ga/TNTs@AC was able to rapidly adsorb and nearly completely remove PFOS within 10 minutes (initial PFOS = 100 µg/L, Ga/TNTs@AC = 3 g/L), and subsequently, degrade 75.0% and mineralize 66.2% of pre-sorbed PFOS within 4-h UV irradiation. The effective PFOS photodegradation also regenerates Ga/TNTs@AC, allowing for repeated uses without invoking chemical regenerants. The superior photoactivity is attributed to the oxygen vacancies, which not only suppresses recombination of the electron/hole pairs, but also facilitates generation of superoxide anions. Both photoactivated holes and superoxide played critical roles in the PFOS degradation, which starts with cleavage of the sulfonate group and converts it into PFOA that is then decarboxylated and defluorinated following the stepwise defluorination mechanism. Ga/TNTs@AC holds the potential for more cost-effective degradation of PFOS and likely other PFAS.

Adsorption and solid-phase photocatalytic degradation of perfluorooctane sulfonate in water using gallium-doped carbon-modified titanate nanotubes

ACS Fall 2021

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