Degradation of Perfluorooctanoic Acid by Chlorine Radical Triggered Electrochemical Oxidation System

Abstract

Electrochemical oxidation (EO) has been shown to have the unique ability to degrade perfluorooctanoic acid (PFOA), although the radical chemistry involved in this degradation is unclear, particularly in the presence of chloride ions (Cl − ). In this study, reaction kinetics, free radical quenching, electron spin resonance, and radical probes were used to examine the roles of •OH and reactive chlorine species (RCS, including Cl•, Cl 2•− , and ClO•) in the EO of PFOA. Using EO in the presence of NaCl, PFOA degradation rates of 89.4%−94.9% and defluorination rates of 38.7%−44.1% were achieved after 480 min with PFOA concentrations ranging from 2.4 to 240 μM. The degradation occurred via the synergistic effect of •OH and Cl• rather than through direct anodic oxidation. The degradation products and density functional theory (DFT) calculations revealed that Cl• triggered the first step of the reaction, thus the initial direct electron transfer was not the rate-limiting step of PFOA degradation. The change in Gibbs free energy of the reaction caused by Cl• was 65.57 kJ mol −1 , which was more than two times lower than that triggered by •OH. However, •OH was involved in the subsequent degradation of PFOA. The synergistic effect of Cl• and •OH in PFOA degradation is demonstrated for the first time in this study, which is promising for the development of electrochemical technology to remove perfluorinated alkyl substances from the environment.

Spontaneous Degradation of the “Forever Chemicals” Perfluoroalkyl and Polyfluoroalkyl Substances (PFASs) on Water Droplet Surfaces

“…In contrast, as depicted in Figures and S11, the degradation initiated by addition of ·OH on the carboxyl group of PFOA to produce a C 7 F 15 –C­(OH) 2 O· intermediate required only a quite low activation free energy (Δ G ‡ = 10.3 kcal·mol –1 ), which is also lower than that in the gaseous and aqueous phase. ,, The C 7 F 15 –C­(OH) 2 O intermediate subsequently loses an H 2 CO 3 group to form a C 7 F 15 · radical (Figure S12). Thus, the degradation is triggered by ·OH rather than e – .…”

Hydrogen Production via Electrolysis of Wastewater

“…Besides •OH, chlorine radicals (•Cl) are also widely used to degrade pollutants due to their high activity and selectivity [54,55]. Urine is an abundant biological pollutant enriched with 80% nitrogen in domestic wastewater.…”

Fluoropolymers as Unique and Irreplaceable Materials: Challenges and Future Trends in These Specific Per or Poly-Fluoroalkyl Substances

“…In addition, Song et al [53] recently succeeded in eliminating PFOA via chlorineradical-triggered electrochemical oxidation, while Chen et al [54] synthesized an original FPNP-embedded hydrogel for PFAS adsorption. These FPNPs were produced from tandem photo-mediated RDRP (Figure 4).…”