Electrochemical Mineralization of Perfluorocarboxylic Acids (PFCAs) by Ce-Doped Modified Porous Nanocrystalline PbO2 Film Electrode

• Published in: Environmental science & technology Vol. 46; no. 18; pp. 10191 - 10198
• Main Authors: Niu, Junfeng, Lin, Hui, Xu, Jiale, Wu, Hao, Li, Yangyang
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 18-09-2012
• Subjects: Applied sciences; Carbon - chemistry; Cerium - chemistry; Electrochemical Techniques - instrumentation; Electrodes; Exact sciences and technology; Fluorocarbons - isolation & purification; General purification processes; Lead - chemistry; Minerals - chemistry; Nanoparticles - chemistry; Oxides - chemistry; Pollution; Porosity; Waste Disposal, Fluid - instrumentation; Waste Water - analysis; Wastewaters; Water Pollutants, Chemical - isolation & purification; Water treatment and pollution; Lead oxide; Emerging contaminant; Electrochemical treatment; Doped materials; Electrode material; Porous material; Persistent organic pollutant; Cerium addition; Electrolysis; Carboxylic acid; Mineralization; Thin layer electrode; Organic fluorine compounds; Physicochemical purification; Waste water purification; Nanostructured materials; Nanocrystal; Organic compounds; Perfluorinated carboxylic acid
• ISSN: 0013-936X; 1520-5851
• DOI: 10.1021/es302148z

The Ce-doped modified porous nanocrystalline PbO2 film electrode prepared by electrodeposition technology was used for electrochemical mineralization of environmentally persistent perfluorinated carboxylic acids (PFCAs) (∼C4–C8), i.e., perfluorobutanoic acid (PFBA), perfluopentanoic acid (PFPeA), perfluorohexanoic acid (PFHxA), perfluoheptanoic acid (PFHpA), and perfluorooctanoic acid (PFOA) in aqueous solution (100 mL of 100 mg L–1). The degradation of PFCAs follows pseudo-first-order kinetics, and the values of the relative rate constant (k) depend upon chain length k PFHpA (4.1 × 10–2 min–1; corresponding half-life 16.8 min) ≈ 1.1k PFOA ≈ 2.5k PFHxA≈ 6.9k PFPeA ≈ 9.7k PFBA. The carbon mineralization indices [i.e., 1 – (TOCinsolution/TOCinPFCA,degraded)] were 0.49, 0.70, 0.84, 0.91, and 0.95 for PFBA, PFPeA, PFHxA, PFHpA, and PFOA, respectively, after 90 min electrolysis. The major mineralization product, F–, as well as low amount of intermediate PFCAs with shortened chain lengths were detected in aqueous solution. By observing the intermediates and tracking the concentration change, a possible pathway of electrochemical mineralization is proposed as follows: Kolbe decarboxylation reaction occurs first at the anode to form the perfluoroalkyl radical, followed by reaction with hydroxyl radicals to form the perfluoroalkyl alcohol which then undergoes intramolecular rearrangement to form the perfluoroalkyl fluoride. After this, the perfluoroalkyl fluoride reforms perfluorinated carboxylic with shorter chain length than its origin by hydrolysis. This electrochemical technique could be employed to treat PFCAs (∼C4–C8) in contaminated wastewater.