Electrochemical Reduction of Perfluorooctanoic Acid (PFOA): An Experimental and Theoretical Approach

Abstract

Perfluorooctanoic acid (PFOA) is an artificial chemical of global concern due to its high environmental persistence and potential human health risk. Electrochemical methods are promising technologies for water treatment because they are efficient, cheap, and scalable. The electrochemical reduction of PFOA is one of the current methodologies. This process leads to defluorination of the carbon chain to hydrogenated products. Here, we describe a mechanistic study of the electrochemical reduction of PFOA in gold electrodes. By using linear sweep voltammetry (LSV), an E 0 ′ of −1.80 V vs Ag/AgCl was estimated. Using a scan rate diagnosis, we determined an electrontransfer coefficient (α exp ) of 0.37, corresponding to a concerted mechanism. The strong adsorption of PFOA into the gold surface is confirmed by the Langmuir-like isotherm in the absence (K A = 1.89 × 10 12 cm 3 mol −1 ) and presence of a negative potential (K A = 3.94 × 10 7 cm 3 mol −1 , at −1.40 V vs Ag/AgCl). Based on Marcus−Hush's theory, calculations show a solvent reorganization energy (λ 0 ) of 0.9 eV, suggesting a large electrostatic repulsion between the perfluorinated chain and water. The estimated free energy of the transition state of the electron transfer (ΔG ‡ = 2.42 eV) suggests that it is thermodynamically the reaction-limiting step. 19 F − 1 H NMR, UV−vis, and mass spectrometry studies confirm the displacement of fluorine atoms by hydrogen. Density functional theory (DFT) calculations also support the concerted mechanism for the reductive defluorination of PFOA, in agreement with the experimental values.

An Atomic and Molecular Insight into How PFOA Reduces α-Helicity, Compromises Substrate Binding, and Creates Binding Pockets in a Model Globular Protein

“…Elsewhere, 21 PFAS compounds found upon post-mortem analysis revealed that in the kidney and lung, perfluorobutanoic acid was the most frequently found PFAS (and at highest concentrations with median values residing at 263 and 807 ng/g in the kidney and lung, respectively). − ,, In the liver and brain, perfluorohexanoic acid showed the maximum levels (median: 68.3 and 141 ng/g, respectively), while perfluorooctanoic acid (PFOA) was the most prevalent PFAS in bone (median: 20.9 ng/g). ,, In the serum of fishery workers, PFAS levels ranged between 0.01 and 10,400 ng/mL, while those exposed to contaminated drinking water presented with levels ranging between 0.5 and 35.5 ng/mL, suggesting that occupational exposure can result in PFAS burdens 1–4 orders of magnitude higher than the general population. , PFAS has been detected in serum from the maternal chord and in newborn blood, demonstrating that these chemicals are capable of passing through the placental barrier. Estimates of the efficiency of placental transfer range between 30% and 79%. , Breast milk has been shown to account for 83–99% of PFAS total daily intake for infants. , Nevertheless, the initial underestimation of their environmental impact together with their widespread use has caused in the last decades an increased level of environmental contamination from poly- and perfluorinated compounds and, in particular, from PFAS. , Although, several efforts have been made for PFAS detection and removal from water − and soil, − addressing the consequences of their historical use remains a critical challenge.…”