Decomposition of Environmentally Persistent Perfluorooctanoic Acid in Water by Photochemical Approaches

Abstract

The decomposition of persistent and bioaccumulative perfluorooctanoic acid (PFOA) in water by UV-visible light irradiation, by H202 with UV-visible light irradiation, and by a tungstic heteropolyacid photocatalyst was examined to develop a technique to counteract stationary sources of PFOA. Direct photolysis proceeded slowly to produce CO2, F-, and short-chain perfluorocarboxylic acids. Compared to the direct photolysis, H2O2 was less effective in PFOA decomposition. On the other hand, the heteropolyacid photocatalyst led to efficient PFOA decomposition and the production of F- ions and CO2. The photocatalyst also suppressed the accumulation of short-chain perfluorocarboxylic acids in the reaction solution. PFOA in the concentrations of 0.34-3.35 mM, typical of those in wastewaters after an emulsifying process in fluoropolymer manufacture, was completely decomposed by the catalyst within 24 h of irradiation from a 200-W xenon-mercury lamp, with no accompanying catalyst degradation, permitting the catalyst to be reused in consecutive runs. Gas chromatography/mass spectrometry (GC/MS) measurements showed no trace of environmentally undesirable species such as CF4, which has a very high global-warming potential. When the (initial PFOA)/(initial catalyst) molar ratio was 10: 1, the turnover number for PFOA decomposition reached 4.33 over 24 h of irradiation.

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). This proves that the water molecule in solution is the main oxidative source.…”

“…It is well known that the efficiency of direct photolysis is limited by quantum efficiency and the intensity of the irradiating light, in which the intensity is increased at the cost of energy consumption (Hori et al, 2004a;Cao et al, 2010). The quantum yield is the number of degraded PFOA molecules divided by the number of photons absorbed by the system.…”

“…The end carbon atom of C 7 F 15 U radical possesses high electric charge intensity (Hori et al, 2004a;Chen et al, 2007), which prefers to react with electrophilic oxidants (Hori et al, 2003a(Hori et al, , 2003b(Hori et al, , 2004bDillert et al, 2007). 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).…”

“…In the case of photochemical decomposition, there have been a number of attempts to promote the degradation of PFOA. Direct photolysis, as a clean technique, is limited by the low degradation efficiency and inadequate mineralization (Hori et al, 2004a). The indirect photoreactions have been developed to improve the efficiency of photo degradation.…”

“…In the electrochemical degradation of PFOA by a boron-doped diamond film electrode, the apparent reaction rate constant increased from 0.108 to 0.444 hr −1 as reaction temperature increased from 20 to 100°C (Xiao et al, 2011). In the photolysis processes for decomposing PFOA, intermediate reactions involved with the water molecules have been reported (Hori et al, 2004a;Chen et al, 2007). However, there have been few reports concerning the temperature effects on the PFOA photolysis degradation.…”