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

Perfluorooctane sulfonate (PFOS) has drawn increasing attention due to its omnipresence and adverse health effects. We prepared a new adsorptive photocatalyst, Ga/TNTs@AC, based on activated carbon and TiO2, and tested the adsorption and subsequent solid-phase photodegradation of PFOS. Ga/TNTs@AC showed faster adsorption kinetics and higher affinity for PFOS than the parent AC, and could degrade 75.0% and mineralize 66.2% of pre-sorbed PFOS within 4-h UV irradiation. The efficient 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 suppressed recombination of the e(-)/h(+) pairs, but also facilitated O-2(center dot-) generation. Both h(+) and O-2(center dot-) 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 PFOS degradation.

Automated summary

The new adsorptive photocatalyst Ga/TNTs@AC showed faster adsorption kinetics and higher affinity for PFOS, degrading and mineralizing a significant percentage of pre-sorbed PFOS within a short UV irradiation time. The efficient PFOS photodegradation regenerates the catalyst for repeated uses without the need for chemical regenerants, attributing to the oxygen vacancies that facilitate O-2(center dot-) generation and suppress recombination of e(-)/h(+) pairs. The degradation of PFOS by Ga/TNTs@AC involves the cleavage of the sulfonate group and conversion into PFOA through a stepwise defluorination mechanism.