Surface fluorination on TiO2 catalyst induced by photodegradation of perfluorooctanoic acid

The effect of oxygen in the photocatalytic oxidation pathways of perfluorooctanoic acid

“…The PFOA degradation passes through the formation of oxygen-centered perfluororadicals, as already reported in the literature [28]. The commonly accepted mechanisms foresee that these radicalic intermediates evolve by producing unstable perfluorinated alcohols, which further decompose to perfluoroacyl fluorides by eliminating hydrofluoric acid [65].…”

“…These findings can be justified by an alternative decomposition mechanism based on the elimination of COF 2 as a decomposition product induced by β-scission reactions of oxyradicals, in competition with the stepwise chain length decrease [28]. Overall, the concentration trends of were 0.008 and 0.002 mM, respectively.…”

“…The PFOA initial concentration ([PFOA] 0 = 4 mM) was maintained lower than its CMC (7.8 mM [48]) in order to avoid the formation of emulsions that would reduce the TiO 2 -promoted photodegradation rates [27,28]. Moreover, the PFOA initial concentration was high enough to allow the detection of the degradation intermediates, even at very low concentrations.…”

“…In particular, PFOA is characterized by a CMC of 0.0078 M and above this value PFOA molecules tend to aggregate in micelles of average dimension around 100 nm, originating a colloid [48]. Below the CMC, PFOA molecules are expected to exhibit lower chemical stability than PFOA aggregates towards the coupled effect of TiO 2 and UV light [28]. On the basis of the optimizations achieved in previous studies [27,28], the general experimental conditions were reported for benchmarking purposes with the experimental TOC concentrations ( Fig.…”

Temperature effect on photolysis decomposing of perfluorooctanoic acid

“…For direct photolysis, the electrophilic oxidants are oxygen in the reaction solution or water molecules of the reaction solution (Niu et al, 2013;Gatto et al, 2015;Mitchell et al, 2013). The C 6 F 13 C 16 O 18 O and C 6 F 13 C 18 O 18 O are the main intermediates resulting from direct irradiation of PFOA in H 2 18 O solutions under high oxygen pressure (Hori et al, 2004a).…”