TiO₂-Induced Heterogeneous Photodegradation of a Fluorotelomer Alcohol in Air

Degradation of C₄F₉C₂H₄OH in air over TiO₂ particles was examined in this first report of gas−solid heterogeneous photochemical degradation of fluorotelomer alcohols (FTOHs), which may be precursors of perfluorocarboxylic acids (PFCAs) in the environment. Photoirradiation (>290 nm) of C₄F₉C₂H₄OH in air flowing over TiO₂ produced CO₂, via C₄F₉CH₂CHO, C₄F₉CHO, C_nF_2n+1COF (n = 2 and/or 3), and COF₂, in that order. X-ray photoelectron spectroscopy of the TiO₂ surface showed a decrease in the amount of fluorine bonded to carbon and an increase in the amount of F^- as the degradation of C₄F₉C₂H₄OH in air proceeded. Of the carbon content in the initial C₄F₉C₂H₄OH (78.8 ppmv), 90.7% was transformed to CO₂, and the predominant fluorine species produced on the TiO₂ surface was F^-. Fluorotelomer unsaturated acids, which are considered to be toxic and have been observed in the biodegradation of FTOHs, did not form. Increased relative humidity in the air accelerated the decomposition of the reaction intermediates, which led to increased CO₂ and F^- formation. This result indicates that humidity is a key factor for counteracting FTOHs in indoor air. Although perfluoroalkyl substances such as PFCAs in water reportedly undergo little photodegradation over TiO₂, our data show that mineralization of C₄F₉C₂H₄OH in air can be achieved with TiO₂.