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Plasma-Assisted Abatement of Per- and Polyfluoroalkyl Substances (PFAS): Thermodynamic Analysis and Validation in Gliding Arc Discharge
Journal article   Open access   Peer reviewed

Plasma-Assisted Abatement of Per- and Polyfluoroalkyl Substances (PFAS): Thermodynamic Analysis and Validation in Gliding Arc Discharge

Mikaela J. Surace, Jimmy Murillo-Gelvez, Mobish A. Shaji, Alexander A. Fridman, Alexander Rabinovich, Erica R. McKenzie, Gregory Fridman and Christopher M. Sales
Plasma, v 6(29), pp 419-434
01 Jul 2023
DOI: https://doi.org/10.3390/plasma6030029
Featured in Collection :   UN Sustainable Development Goals @ Drexel
url
https://doi.org/10.3390/plasma6030029View
Published, Version of Record (VoR)CC BY V4.0,  Open

Abstract

gliding arc discharges plasma treatment of PFAS-contaminated water thermodynamics of PFOA mineralization
Per- and polyfluoroalkyl substances (PFAS) are a group of synthetic organofluorine surfactants that are resistant to typical methods of degradation. Thermal techniques along with other novel, less energy-intensive techniques are currently being investigated for the treatment of PFAS-contaminated matrices. Non-equilibrium plasma is one technique that has shown promise for the treatment of PFAS-contaminated water. To better tailor non-equilibrium plasma systems for this application, knowledge of the energy required for mineralization, and in turn the roles that plasma reactive species and heat can play in this process, would be useful. In this study, fundamental thermodynamic equations were used to estimate the enthalpies of reaction (480 kJ/mol) and formation (−4640 kJ/mol) of perfluorooctanoic acid (PFOA, a long-chain legacy PFAS) in water. This enthalpy of reaction estimate indicates that plasma reactive species alone cannot catalyze the reaction; because the reaction is endothermic, energy input (e.g., heat) is required. The estimated enthalpies were used with HSC Chemistry software to produce a model of PFOA defluorination in a 100 mg/L aqueous solution as a function of enthalpy. The model indicated that as enthalpy of the reaction system increased, higher PFOA defluorination, and thus a higher extent of mineralization, was achieved. The model results were validated using experimental results from the gliding arc plasmatron (GAP) treatment of PFOA or PFOS-contaminated water using argon and air, separately, as the plasma gas. It was demonstrated that PFOA and PFOS mineralization in both types of plasma required more energy than predicted by thermodynamics, which was anticipated as the model did not take kinetics into account. However, the observed trends were similar to that of the model, especially when argon was used as the plasma gas. Overall, it was demonstrated that while energy input (e.g., heat) was required for the non-equilibrium plasma degradation of PFOA in water, a lower energy barrier was present with plasma treatment compared to conventional thermal treatments, and therefore mineralization was improved. Plasma reactive species, such as hydroxyl radicals ( ⋅OH ) and/or hydrated electrons (e−(aq)), though unable to accelerate an endothermic reaction alone, likely served as catalysts for PFOA mineralization, helping to lower the energy barrier. In this study, the activation energies (Ea) for these species to react with the alpha C–F bond in PFOA were estimated to be roughly 1 eV for hydroxyl radicals and 2 eV for hydrated electrons.

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18 citations in Web of Science
10 citations in Scopus

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UN Sustainable Development Goals (SDGs)

This publication has contributed to the advancement of the following goals:

#6 Clean Water and Sanitation
#3 Good Health and Well-Being

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Collaboration types
Domestic collaboration
Web of Science research areas
Physics, Fluids & Plasmas
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