New Indole Derivative Heterogeneous System for the Synergistic Reduction and Oxidation of Various Per-/Polyfluoroalkyl Substances: Insights into the Degradation/Defluorination Mechanism

Wang, Zhe; Jin, Xin; Hong, Ran; Wang, Xinhao; Chen, Zhanghao; Gao, Guandao; He, Huan; Liu, Jinyong; Gu, Cheng

doi:10.1021/acs.est.3c05940

“…After bulk electrolysis, a m / z of 394.96 m / z is observed. This mass is attributed to the monohydrogenated species [C 7 F 14 H–COO] − which has previously been reported as a reduction product . In addition, a m / z of 374.97 corresponding to the monounsaturated chain [C 7 F 13 –COO] − is observed.…”

Section: Resultsmentioning

confidence: 56%

“…These results are consistent with our experimentally observed reduction potentials and support a concerted mechanism for the reductive PFOA C–F dissociation. Other reports have obtained reduction potentials in the range of −2.50 to −2.95 V vs SHE …”

Section: Resultsmentioning

confidence: 89%

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

Calvillo Solís,

Sandoval-Pauker,

Bai

et al. 2024

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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.

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“…Interest-ingly, the product C 7 F 14 HCOO À exhibited 5 isomer peaks (Figure S9), suggesting that hydrodefluorination might occur to the different sites of the perfluoroalkyl chain. [26] The Fukui function calculation suggests that nucleophilic attacking is likely to occur on all the F saturated C centers of PFOA, PFOS and 6 : 3-FTCA (Figure S10). Further DFT calculation predicts that O 2 *À nucleophilic attacking either the α-CF 2 -(next to carboxyl group) or the middle chain -CF 2 -encounters the transient energy barrier (TS α1 ) of 40-65 kcal/mol (Figure S11).…”

Section: Methodsmentioning

confidence: 99%

Electrostatic Field in Contact‐Electro‐Catalysis Driven C−F Bond Cleavage of Perfluoroalkyl Substances

Wang,

Zhang,

Zhang

et al. 2024

Angewandte Chemie

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Perfluoroalkyl substances (PFASs) are persistent and toxic to human health. It is demanding for high‐efficient and green technologies to remove PFASs from water. In this study, a novel PFAS treatment technology was developed, utilizing polytetrafluoroethylene (PTFE) particles (1~5 μm) as the catalyst and a low frequency ultrasound (US, 40 kHz, 0.3 W/cm2) for activation. Remarkably, this system can induce near‐complete defluorination for different structured PFASs. The underlying mechanism relies on contact electrification between PTFE and water, which induces cumulative electrons on PTFE surface, and creates a high surface voltage (tens of volts). Such high surface voltage can generate abundant reactive oxygen species (ROS, i.e., O2•–, HO•, etc.) and a strong interfacial electrostatic field (IEF of 109~1010 V/m). Consequently, the strong IEF significantly activates PFAS molecules and reduces the energy barrier of O2•– nucleophilic reaction. Simultaneously, the co‐existence of surface electrons (PTFE*(e−)) and HO• enables synergetic reduction and oxidation of PFAS and its intermediates, leading to enhanced and thorough defluorination. The US/PTFE method shows compelling advantages of low energy consumption, zero chemical input, and few harmful intermediates. It offers a new and promising solution for effectively treating the PFAS‐contaminated drinking water.

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Electrostatic Field in Contact‐Electro‐Catalysis Driven C−F Bond Cleavage of Perfluoroalkyl Substances

Wang,

Zhang,

Zhang

et al. 2024

Angew Chem Int Ed

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7

0

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Perfluoroalkyl substances (PFASs) are persistent and toxic to human health. It is demanding for high‐efficient and green technologies to remove PFASs from water. In this study, a novel PFAS treatment technology was developed, utilizing polytetrafluoroethylene (PTFE) particles (1~5 μm) as the catalyst and a low frequency ultrasound (US, 40 kHz, 0.3 W/cm2) for activation. Remarkably, this system can induce near‐complete defluorination for different structured PFASs. The underlying mechanism relies on contact electrification between PTFE and water, which induces cumulative electrons on PTFE surface, and creates a high surface voltage (tens of volts). Such high surface voltage can generate abundant reactive oxygen species (ROS, i.e., O2•–, HO•, etc.) and a strong interfacial electrostatic field (IEF of 109~1010 V/m). Consequently, the strong IEF significantly activates PFAS molecules and reduces the energy barrier of O2•– nucleophilic reaction. Simultaneously, the co‐existence of surface electrons (PTFE*(e−)) and HO• enables synergetic reduction and oxidation of PFAS and its intermediates, leading to enhanced and thorough defluorination. The US/PTFE method shows compelling advantages of low energy consumption, zero chemical input, and few harmful intermediates. It offers a new and promising solution for effectively treating the PFAS‐contaminated drinking water.

show abstract

New Indole Derivative Heterogeneous System for the Synergistic Reduction and Oxidation of Various Per-/Polyfluoroalkyl Substances: Insights into the Degradation/Defluorination Mechanism

Cited by 7 publications

References 46 publications

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

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

Electrostatic Field in Contact‐Electro‐Catalysis Driven C−F Bond Cleavage of Perfluoroalkyl Substances

Electrostatic Field in Contact‐Electro‐Catalysis Driven C−F Bond Cleavage of Perfluoroalkyl Substances

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