Electrochemical degradation of PFOA using unmodified graphite electrodes: a scalable approach for PFAS remediation

Perfluorooctanoic acid (PFOA) is a category of PFAS (per- and polyfluoroalkyl substances), particularly prevalent in aquatic environments, and this study investigated the effectiveness of electrochemical oxidation using cost-effective graphite electrodes for PFOA degradation with sodium sulfate as the supporting electrolyte. Optimization studies revealed maximum degradation efficiency at pH 3, 45 mA/cm² current density, 20 mM electrolyte concentration, and 4-h treatment time. Under these conditions, the system achieved 85% total organic carbon (TOC) removal, 84.19% PFOA degradation confirmed by high-resolution mass spectrometry, and defluorination, demonstrating substantial mineralization of PFOA. High-resolution mass spectrometry identified a degradation pathway proceeding through defluorination, decarboxylation, hydroxylation, and dehydroxylation mechanisms, with heptafluoropropane identified as the final organic intermediate before complete mineralization to CO₂, H₂O, and fluoride ions. The system followed a decarboxylation-hydroxylation-elimination-hydrolysis (DHEH) mechanism. Ion chromatography confirmed significant defluorination, with fluoride concentrations increasing from 13.1 to 884.33 μg/L. Characterization of electrodes revealed surface modifications that enhanced electrochemical activity while maintaining structural integrity. These findings demonstrate that graphite electrodes offer a cost-effective alternative to expensive boron-doped diamond electrodes for PFOA removal while maintaining comparable performance.