On the Role of the Cathode for the Electro-Oxidation of Perfluorooctanoic Acid

Abstract

Perfluorooctanoic acid (PFOA), C7F15COOH, has been widely employed over the past fifty years, causing an environmental problem because of its dispersion and low biodegradability. Furthermore, the high stability of this molecule, conferred by the high strength of the C-F bond makes it very difficult to remove. In this work, electrochemical techniques are applied for PFOA degradation in order to study the influence of the cathode on defluorination. For this purpose, boron-doped diamond (BDD), Pt, Zr, and stainless steel have been tested as cathodes working with BDD anode at low electrolyte concentration (3.5 mM) to degrade PFOA at 100 mg/L. Among these cathodic materials, Pt improves the defluorination reaction. The electro-degradation of a PFOA molecule starts by a direct exchange of one electron at the anode and then follows a complex mechanism involving reaction with hydroxyl radicals and adsorbed hydrogen on the cathode. It is assumed that Pt acts as an electrocatalyst, enhancing PFOA defluorination by the reduction reaction of perfluorinated carbonyl intermediates on the cathode. The defluorinated intermediates are then more easily oxidized by HO• radicals. Hence, high mineralization (xTOC: 76.1%) and defluorination degrees (xF−: 58.6%) were reached with Pt working at current density j = 7.9 mA/cm2. This BDD-Pt system reaches a higher efficiency in terms of defluorination for a given electrical charge than previous works reported in literature. Influence of the electrolyte composition and initial pH are also explored.

Installation of synergistic binding sites onto porous organic polymers for efficient removal of perfluorooctanoic acid

“…Among various technologies used for PFAS removal from contaminated water such as oxidative 6 , UV irradiation 7 , sonochemical 8 , and electrochemical methods 9 , adsorption is highly favored owing to its simplicity and high efficiency in the purification process of contaminated water 10 . Thus, a wide range of adsorbents have been investigated for PFAS elimination from polluted waters.…”

Electrochemical Oxidation of Perfluorooctanesulfonate by Magnéli Phase Ti4O7 Electrode in the Presence of Trichloroethylene

“…The pseudo-first order rate constants (kobs) of PFOS removal were 0.0471 and 0.0254 min -1 without and with TCE, respectively. It was proposed that PFOS can be oxidized at anode through direct electron transfer and then followed by reactions with HO• at anode and/or adsorbed hydrogen at cathode to release fluoride [26,39]. Hydroxyl radicals can be in situ generated from water electrolysis when the anode potential is greater than 2.38 V (vs. SHE) [23].…”

“…This suggested significant defluorination of PFOS upon EO treatment, and it appeared to be not influenced by the presence of TCE. Recent studies suggested that the reduction reactions at cathode enhanced the fluoride release of PFASs in the EO process [39]. Although the presence of TCE inhibited PFOS removal by competing for electron transfer sites and HO• at anode, the defluorination at cathode might not be inhibited and played a role.…”

Rate, Efficiency, and Mechanisms of Electrochemical Perfluorooctanoic Acid Degradation with Boron-Doped Diamond and Plasma Electrodes

“…Examples of separation-based methods include adsorption, − ion exchange, , membrane separation, , and foam fractionation. − More recently, electrosorption-based technologies have demonstrated potential for selectively removing PFAS through functional surfaces. − Although these methods can physically remove PFAS from water, the PFAS ultimately remains as a persistent waste that needs to be chemically degraded. Examples of degradation-based methods include sonolysis, ,, photochemical, − electrochemical, ,− and plasma − processes. In the last decade, electrochemical and plasma-based processes have attracted much attention because of their capability to mineralize PFAS into F – and CO 2 .…”

“…A BDD electrode was chosen as the conventional electrode since it is known to be corrosion-resistant and stable at high current densities . Furthermore, it has a wide potential window and a high overpotential for O 2 generation, thereby constituting the state-of-the-art electrode for the oxidation of PFAS. ,− ,− Both BDD and plasma electrodes were used in the same cell under the same mixing conditions, and the currents employed were comparable. Long-chain, surface-active PFAS molecules are especially prevalent contaminants; therefore, perfluorooctanoic acid (PFOA) was selected as the model PFAS compound.…”