The effects of surface oxidation and fluorination of boron-doped diamond anodes on perchlorate formation and organic compound oxidation

Jawando, Wuraola; Gayen, Pralay; Chaplin, Brian P.

doi:10.1016/j.electacta.2015.06.034

Cited by 24 publications

(22 citation statements)

References 64 publications

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“…This indicates that F element was introduced to the anode surface during EO treatment of PFOS. A similar phenomenon was observed with EO treatment of PFOA using BDD anode in earlier studies. , …”

Section: Resultssupporting

confidence: 88%

“…There could be products that were not identified, or the released fluoride may not be fully recovered. For example, fluoride may be bound to the anode surface that was not recoverable during EO treatment of PFAS Figure c displays the X-ray photoelectron spectroscopy (XPS) characterizations of the titanium suboxide particles that were scraped from the anode surface before and after electrooxidation treatment of PFOS.…”

Section: Resultsmentioning

confidence: 99%

See 1 more Smart Citation

Degradation of Perfluorooctanesulfonate by Reactive Electrochemical Membrane Composed of Magnéli Phase Titanium Suboxide

Shi

Wang

et al. 2019

Environ. Sci. Technol.

120

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This study investigated the degradation of perfluorooctanesulfonate (PFOS) in a reactive electrochemical membrane (REM) system in which a porous Magneĺi phase titanium suboxide ceramic membrane served simultaneously as the anode and the membrane. Near complete removal (98.30 ± 0.51%) of PFOS was achieved under a cross-flow filtration mode at the anodic potential of 3.15 V vs standard hydrogen electrode (SHE). PFOS removal efficiency during the REM operation is much greater than that of the batch operation mode under the same anodic potential. A systematic reaction rate analysis in combination with electrochemical characterizations quantitatively elucidated the enhancement of PFOS removal in REM operation in relation to the increased electroactive surface area and improved interphase mass transfer. PFOS appeared to undergo rapid mineralization to CO 2 and F − , with only trace levels of short-chain perfluorocarboxylic acids (PFCAs, C 4 −C 8 ) identified as intermediate products. Density functional theory (DFT) simulations and experiments involving free radical scavengers indicated that PFOS degradation was initiated by direct electron transfer (DET) on anode to yield PFOS free radicals (PFOS • ), which further react with hydroxyl radicals that were generated by water oxidation and adsorbed on the anode surface ( • OH ads ). The attack of • OH ads is essential to PFOS degradation, because, otherwise, PFOS • may react with water and revert to PFOS.

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Section: Resultssupporting

confidence: 88%

Section: Resultsmentioning

confidence: 99%

Degradation of Perfluorooctanesulfonate by Reactive Electrochemical Membrane Composed of Magnéli Phase Titanium Suboxide

Shi

Wang

et al. 2019

Environ. Sci. Technol.

120

View full text Add to dashboard Cite

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“…Similarly, the O–H dissociation constants K a of aliphatic alcohols are small: K a ≈ 10 –18 for tert -butanol, corresponding to free-energy changes of ∼100 kJ mol –1 . These values show that although oxidized BDD (O-BDD) surfaces may have a number of species, − these do not necessarily provide labile sites for inner-sphere electrochemical reactions. , One potentially important property controlling electrochemical pathways on diamond is surface hydrophobicity, which impacts the organization of the adjacent water molecules. , Surface hydrophobicity can be manipulated via direct fluorination of diamond − (F-BDD) and by functionalization with polyfluorinated ligands (PF-BDD) . These surface modifications have been shown to yield very hydrophobic surfaces with only very weak interaction with water. , The high C–F bond strength (calculated at 506 kJ mol –1 ) suggests that using fluorinated surfaces or ligands provides a robust way to potentially alter the relative rates of O 2 and • OH production.…”

Section: Introductionmentioning

confidence: 99%

Enhancing Electrochemical Efficiency of Hydroxyl Radical Formation on Diamond Electrodes by Functionalization with Hydrophobic Monolayers

et al. 2018

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Electrochemical formation of high-energy species such as hydroxyl radicals in aqueous media is inefficient because oxidation of H2O to form O2 is a more thermodynamically favorable reaction. Boron-doped diamond (BDD) is widely used as an electrode material for generating •OH radicals because it has a very large kinetic overpotential for O2 production, thus increasing electrochemical efficiency for •OH production. Yet, the underlying mechanisms of O2 and •OH production at diamond electrodes are not well understood. We demonstrate that boron-doped diamond surfaces functionalized with hydrophobic, polyfluorinated molecular ligands (PF-BDD) have significantly higher electrochemical efficiency for •OH production compared with hydrogen-terminated (H-BDD), oxidized (O-BDD), or poly(ethylene ether)-functionalized (E-BDD) boron-doped diamond samples. Our measurements show that •OH production is nearly independent of surface functionalization and pH (pH = 7.4 vs 9.2), indicating that •OH is produced by oxidation of H2O in an outer-sphere electron-transfer process. In contrast, the total electrochemical current, which primarily produces O2, differs strongly between samples with different surface functionalizations, indicating an inner-sphere electron-transfer process. X-ray photoelectron spectroscopy measurements show that although both H-BDD and PF-BDD electrodes are oxidized over time, PF-BDD showed longer stability (≈24 h of use) than H-BDD. This work demonstrates that increasing surface hydrophobicity using perfluorinated ligands selectively inhibits inner-sphere oxidation to O2 and therefore provides a pathway to increased efficiency for formation of •OH via an outer-sphere process. The use of hydrophobic electrodes may be a general approach to increasing selectivity toward outer-sphere electron-transfer processes in aqueous media.

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“…After DET oxidation (eq ), the surface-bound Cl • is oxidized to free chlorine (HClO/OCl – ), , which undergoes a combination of DET oxidation and • OH-mediated oxidation to form ClO 4 – (reactions 8–15 in Table S3). , The rates of the reactions described above were calibrated by fitting the measured Cl – , free chlorine, ClO 3 – , and ClO 4 – concentrations as functions of electrolysis time (Figure S2a). All of the model fitting results achieved R 2 values of >0.95.…”

Section: Resultsmentioning

confidence: 99%

Inhibition of Perchlorate Formation during the Electrochemical Oxidation of Perfluoroalkyl Acid in Groundwater

Yang

Fernando

Holsen

et al. 2019

Environ. Sci. Technol. Lett.

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Perfluorooctanoic acid (PFOA) and perfluorooctanesulfonate (PFOS) are groundwater contaminants of emerging concern due to their toxicity and persistence. Currently, there are limited destructive treatment options for this type of water. One promising approach is electrochemical oxidation (EO) using a boron-doped diamond (BDD) anode. However, during EO treatment, chloride in water is readily converted to perchlorate (ClO 4 − ), which is an endocrine disruptor. This is a common dilemma for EO techniques: anodes with higher EO activity tend to produce more ClO 4 − . In this study, we used the BDD anode as a model anode to treat PFOA and PFOS in a chloride-bearing electrolyte. We found that the formation of ClO 4 − can be largely inhibited without compromising the efficiency of PFOA and PFOS destruction by adding hydrogen peroxide (≥50 mM H 2 O 2 ). Experimental approaches and computational kinetic modeling indicate that H 2 O 2 inhibits ClO 4− formation by quenching chlorine and hydroxyl radicals and the oxidation of PFOA and PFOS is primarily determined by direct electron transfer oxidation, regardless of the dominant radical species. This facile strategy suppressed 88% of ClO 4 − formation during EO treatment of groundwater spiked with PFOA and PFOS.

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The effects of surface oxidation and fluorination of boron-doped diamond anodes on perchlorate formation and organic compound oxidation

Cited by 24 publications

References 64 publications

Degradation of Perfluorooctanesulfonate by Reactive Electrochemical Membrane Composed of Magnéli Phase Titanium Suboxide

Degradation of Perfluorooctanesulfonate by Reactive Electrochemical Membrane Composed of Magnéli Phase Titanium Suboxide

Enhancing Electrochemical Efficiency of Hydroxyl Radical Formation on Diamond Electrodes by Functionalization with Hydrophobic Monolayers

Inhibition of Perchlorate Formation during the Electrochemical Oxidation of Perfluoroalkyl Acid in Groundwater

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