While considered a gold standard for photocatalytic degradation of more conventional organic water contaminants, TiO2 is known to be ineffective at degrading the highly recalcitrant poly-/perfluoroalkyl substances (PFAS), compared to alternative semiconductor materials. A variety of reasons for its poor activity toward PFAS have been speculated in the literature, including insufficient redox potential and excessive electron-hole recombination rates. Furthermore, several works have reported greatly enhanced PFOA degradation rates by TiO2 modified with graphitic carbon cocatalysts, such as graphene oxides and activated carbon. The enhancement was typically attributed to the electron withdrawing ability of the conductive carbon material, and thus improved electron-hole separation. Herein, we provide evidence that PFOA degradation enhancement by graphene oxide (GO)-modified TiO2 is unrelated to charge carrier separation, but instead attributed to unique PFOA adsorption sites created at the semiconductor-GO interface. This adsorption is speculated to arise from a combination of electrostatic attraction by the positively-charge TiO2 surface and hydrophobic interaction by the GO, and to yield more intimate Ti4+-PFOA interaction for improved charge transfer. We furthermore demonstrated even greater PFOA degradation rate enhancements (up to 50%) when TiO2 was modified with hydrophobic materials that are not conductive or semiconductive, including polytetrafluoroethylene and polyethylene microparticles. These findings suggest that hydrophobic materials offer a unique mechanism of photocatalysis enhancement for development of future PFAS-active catalysts.

Revised mechanism for explaining PFOA degradation enhancement by the use of graphitic carbon with semiconductor photocatalytic materials

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ACS Fall 2022

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.