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 H₂O₂ 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.