Photocatalytic decomposition of perfluorooctanoic acid (PFOA) by TiO₂ in the presence of oxalic acid

• Published in: Journal of hazardous materials 2011-09, Vol.192 (3), p.1869-1875
• Main Authors: Wang, Yuan, Zhang, Pengyi
• Format: Article
• Language: English
• Subjects: acidity; Anions; Applied sciences; Caprylates - chemistry; carbon dioxide; Catalysis; Catalytic reactions; Chemical engineering; Chemistry; Chemistry Techniques, Analytical; Decomposition; Electron paramagnetic resonance; electron paramagnetic resonance spectroscopy; Electron Spin Resonance Spectroscopy; Electrons; Exact sciences and technology; Fluorocarbons - chemistry; formic acid; Free Radicals; General and physical chemistry; Light; nitrogen; Nitrogen - chemistry; Oxalic acid; Oxalic Acid - chemistry; Perchlorates - chemistry; Perchloric acid; Photocatalysis; Photochemistry - methods; Pollution; potassium; potassium iodide; Potassium Iodide - chemistry; Potassium iodides; Reactors; Theory of reactions, general kinetics. Catalysis. Nomenclature, chemical documentation, computer chemistry; Titanium - chemistry; Titanium dioxide; ultraviolet radiation; Ultraviolet Rays; Water Pollutants, Chemical - analysis; Water Purification - methods
• ISSN: 0304-3894; 1873-3336
• DOI: 10.1016/j.jhazmat.2011.07.026

Heterogeneous photocatalytic decomposition of perfluoroocatanoic acid (PFOA) by TiO₂ under 254nm UV light was investigated. Adding oxalic acid as a hole-scavenger significantly accelerated PFOA decomposition under nitrogen atmosphere. Fluoride ion, formic acid and six shorter-chain perfluorinated carboxylic acids (PFCAs) bearing C₂–C₇ were identified as intermediates. When using perchloric acid (HClO₄) as a replacement of oxalic acid to maintain the same pH of the reaction solution, PFOA did not decomposition efficiently. Compared with oxalic acid, potassium iodide (KI, another hole-scavenger) also led to a slower PFOA decomposition, while the addition of an electron acceptor (potassium persulfate, K₂S₂O₈) obviously inhibited PFOA decomposition. This suggested that oxalic acid played more than one role in PFOA decomposition rather than simply providing acidity and acting as a hole-scavenger. The electron paramagnetic resonance (EPR) measurements confirmed the existence of carboxyl anion radicals (CO₂ ⁻) in the photocatalytic process, which was a result of the reaction between oxalic acid and photogenerated hole. These findings indicated that PFOA decomposition was primarily induced by CO₂ ⁻ radicals, although photogenerated electron was also conducive to PFOA decomposition. A possible mechanism for PFOA decomposition was proposed.