Electrochemical Degradation of PFOA Using Graphite-Sheet Electrodes: Kinetics and Mechanisms

Abstract

Per- and polyfluoroalkyl substances (PFAS) are persistent, bioaccumulative, and toxic contaminants characterized by highly stable fluorinated alkyl chains. Due to their chemical resilience, PFAS are frequently detected in both influents and effluents of conventional wastewater treatment plants, where they undergo minimal to no removal. Electrooxidation offers a promising, chemical-free approach for PFAS remediation, but it typically relies on expensive, high-performance electrodes such as boron-doped diamond (BDD) or titanium-based materials, limiting scalability and practical deployment. This study establishes the use of low-cost, unmodified, flexible graphite sheet electrodes as anodes for the electrochemical degradation of perfluorooctanoic acid (PFOA). The degradation efficiency was assessed under varying conditions, including initial PFOA concentrations (5–1,000 μg·L–1), current densities (2.5–12.5 mA.cm–2), pH (3–9), electrolyte concentrations (0–0.05 M NaCl), and the presence of reactive radical species. Under optimized conditions (0.05 M NaCl, 10 mA.cm–2, pH ≈ 6), ∼99% PFOA degradation was achieved within 90 min at an initial concentration of 10 μg·L–1, with a corresponding energy consumption of 16.09 kWh.m–3 per order. Hydroxyl radicals and chlorine-based reactive species were identified as key contributors to the degradation mechanism. However, degradation efficiency was inhibited in the presence of a complex wastewater matrix, consistent with the known limitations of radical-mediated processes. Liquid chromatography–mass spectrometry (LC-MS) analysis of the 90 min sample revealed the formation of intermediate degradation products, including shorter-chain perfluoroalkyl carboxylic acids such as perfluoroheptanoic acid (PFHpA), perfluorohexanoic acid (PFHxA), perfluoropentanoic acid (PFPeA), and perfluorobutanoic acid (PFBA). Overall, the electrochemical oxidation approach demonstrated in this study offers a promising, economically attractive alternative for the degradation of PFAS in contaminated groundwater and wastewater.