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Abeywardane K, Goldsmith CF. Accurate Enthalpies of Formation for PFAS from First-Principles: Combining Different Levels of Theory in a Generalized Thermochemical Hierarchy. ACS PHYSICAL CHEMISTRY AU 2024; 4:247-258. [PMID: 38800729 PMCID: PMC11117692 DOI: 10.1021/acsphyschemau.3c00056] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 10/25/2023] [Revised: 01/05/2024] [Accepted: 01/08/2024] [Indexed: 05/29/2024]
Abstract
The enthalpies of formation are computed for a large number of per- and poly fluoroalkyl substances (PFAS) using a connectivity-based hierarchy (CBH) approach. A combination of different electronic structure methods are used to provide the reference data in a hierarchical manner. The ANL0 method, in conjunction with the active thermochemical tables, provides enthalpies of formation for smaller species with subchemical accuracy. Coupled-cluster theory with explicit correlations are used to compute enthalpies of formation for intermediate species, based upon the ANL0 results. For the largest PFAS, including perfluorooctanoic acid (PFOA) and heptafluoropropylene oxide dimer acid (GenX), coupled-cluster theory with local correlations is used. The sequence of homodesmotic reactions proposed by the CBH are determined automatically by a new open-source code, AutoCBH. The results are the first reported enthalpies of formation for the majority of the species. A convergence analysis and global uncertainty quantification confirm that the enthalpies of formation at 0 K should be accurate to within ±5 kJ/mol. This new approach is not limited to PFAS, but can be applied to many chemical systems.
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Affiliation(s)
- Kento Abeywardane
- Chemical Engineering Group, School
of Engineering, Brown University, Providence, Rhode Island 02912, United States
| | - C. Franklin Goldsmith
- Chemical Engineering Group, School
of Engineering, Brown University, Providence, Rhode Island 02912, United States
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2
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Liu Z, Jin B, Rao D, Bentel MJ, Liu T, Gao J, Men Y, Liu J. Oxidative Transformation of Nafion-Related Fluorinated Ether Sulfonates: Comparison with Legacy PFAS Structures and Opportunities of Acidic Persulfate Digestion for PFAS Precursor Analysis. ENVIRONMENTAL SCIENCE & TECHNOLOGY 2024; 58:6415-6424. [PMID: 38528735 PMCID: PMC11008247 DOI: 10.1021/acs.est.3c06289] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/04/2023] [Revised: 03/09/2024] [Accepted: 03/11/2024] [Indexed: 03/27/2024]
Abstract
The total oxidizable precursor (TOP) assay has been extensively used for detecting PFAS pollutants that do not have analytical standards. It uses hydroxyl radicals (HO•) from the heat activation of persulfate under alkaline pH to convert H-containing precursors to perfluoroalkyl carboxylates (PFCAs) for target analysis. However, the current TOP assay oxidation method does not apply to emerging PFAS because (i) many structures do not contain C-H bonds for HO• attack and (ii) the transformation products are not necessarily PFCAs. In this study, we explored the use of classic acidic persulfate digestion, which generates sulfate radicals (SO4-•), to extend the capability of the TOP assay. We examined the oxidation of Nafion-related ether sulfonates that contain C-H or -COO-, characterized the oxidation products, and quantified the F atom balance. The SO4-• oxidation greatly expanded the scope of oxidizable precursors. The transformation was initiated by decarboxylation, followed by various spontaneous steps, such as HF elimination and ester hydrolysis. We further compared the oxidation of legacy fluorotelomers using SO4-• versus HO•. The results suggest novel product distribution patterns, depending on the functional group and oxidant dose. The general trends and strategies were also validated by analyzing a mixture of 100000- or 10000-fold diluted aqueous film-forming foam (containing various fluorotelomer surfactants and organics) and a spiked Nafion precursor. Therefore, (1) the combined use of SO4-• and HO• oxidation, (2) the expanded list of standard chemicals, and (3) further elucidation of SO4-• oxidation mechanisms will provide more critical information to probe emerging PFAS pollutants.
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Affiliation(s)
- Zekun Liu
- Department
of Chemical & Environmental Engineering, University of California, Riverside, California 92521, United States
- Claros
Technologies Inc., Minneapolis, Minnesota 55413, United States
| | - Bosen Jin
- Department
of Chemical & Environmental Engineering, University of California, Riverside, California 92521, United States
| | - Dandan Rao
- Department
of Chemical & Environmental Engineering, University of California, Riverside, California 92521, United States
| | - Michael J. Bentel
- Department
of Chemical & Environmental Engineering, University of California, Riverside, California 92521, United States
| | - Tianchi Liu
- Department
of Chemical & Environmental Engineering, University of California, Riverside, California 92521, United States
| | - Jinyu Gao
- Department
of Chemical & Environmental Engineering, University of California, Riverside, California 92521, United States
| | - Yujie Men
- Department
of Chemical & Environmental Engineering, University of California, Riverside, California 92521, United States
| | - Jinyong Liu
- Department
of Chemical & Environmental Engineering, University of California, Riverside, California 92521, United States
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Zhang H, Zhu L, Zhang Y, Héroux P, Cai L, Liu Y. Removal of per- and polyfluoroalkyl substances from water by plasma treatment: Insights into structural effects and underlying mechanisms. WATER RESEARCH 2024; 253:121316. [PMID: 38377926 DOI: 10.1016/j.watres.2024.121316] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/08/2023] [Revised: 02/09/2024] [Accepted: 02/13/2024] [Indexed: 02/22/2024]
Abstract
Non-thermal plasma emerges as a promising technology for per- and polyfluoroalkyl substances (PFAS) decomposition due to its notable efficacy and environmentally friendly characteristics. In this study, we demonstrated the efficacy of a falling film dielectric barrier discharge (DBD) system for the removal of 10 PFAS, including perfluoroalkyl carboxylic acids (PFCAs), perfluoroalkyl sulfonic acids (PFSAs) and hexafluoropropylene oxide (HFPO) oligomer acids. Results showed that compounds with fluoroalkyl chain length>4 were effectively decomposed within 100 min, with long-chain PFAS demonstrating more pronounced removal performance than their short-chain analogues. The superior removal but low defluorination observed in HFPO oligomer acids could be ascribed to their ether-based structural features. The integration of experimental results with density functional theory (DFT) calculations revealed that the synergistic effects of various reactive species are pivotal to their efficient decomposition, with electrons, OH•, and NO2• playing essential roles. In contrast, the degradation of PFSAs was more dependent on electron attack than that of PFCAs and HFPO oligomer acids. Significantly, the most crucial degradation pathway for HFPO oligomer acids was the cleavage of ether CO, whether through radical or electron attack. Furthermore, the demonstrated effective removal in various water matrices showed the potential of the plasma system for removing PFAS in complex aquatic environments. This study provided mechanistic insights into PFAS degradation behavior in plasma processes, and it underscored the vital influence of molecular structures on degradability, thereby contributing to the further development and regulation of plasma-based technologies for treating PFAS in water.
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Affiliation(s)
- Han Zhang
- College of Environmental Science and Engineering, Donghua University, 2999 North Renmin Road, Shanghai 201620, China
| | - Luxiang Zhu
- College of Environmental Science and Engineering, Donghua University, 2999 North Renmin Road, Shanghai 201620, China
| | - Yinyin Zhang
- College of Environmental Science and Engineering, Donghua University, 2999 North Renmin Road, Shanghai 201620, China
| | - Paul Héroux
- Department of Epidemiology, Biostatistics and Occupational Health, McGill University, Montreal, Canada
| | - Li Cai
- College of Environmental Science and Engineering, Donghua University, 2999 North Renmin Road, Shanghai 201620, China
| | - Yanan Liu
- College of Environmental Science and Engineering, Donghua University, 2999 North Renmin Road, Shanghai 201620, China; Shanghai institute of pollution control and ecological security, Shanghai 200092, China.
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Kim J, Kim T, Park H, Kim MK, Eom S, Choe Y, Choe JK, Zoh KD. Kinetics and proposed mechanisms of hexafluoropropylene oxide dimer acid (GenX) degradation via vacuum-UV (VUV) photolysis and VUV/sulfite processes. JOURNAL OF HAZARDOUS MATERIALS 2024; 463:132864. [PMID: 37907009 DOI: 10.1016/j.jhazmat.2023.132864] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/14/2023] [Revised: 07/04/2023] [Accepted: 10/24/2023] [Indexed: 11/02/2023]
Abstract
We investigated the degradation of hexafluoropropylene oxide dimer acid (GenX) in water via VUV photolysis and VUV/sulfite reactions under nitrogen-saturated conditions. Approximately 35% and 90% of GenX were degraded in 3 h in the VUV photolysis and VUV/sulfite reaction. While GenX removal rate was highest at pH 6 in VUV photolysis, it increased under alkaline pHs, especially at pH 10, in VUV/sulfite reaction. Radical scavenging experiments showed that, while both eaq- and •H contributed to VUV photolysis, eaq- played a significant role and •OH had a negative effect during VUV/sulfite reaction. Two transformation products (TPs) (TFA and PFPrA) were identified in VUV photolysis, whereas five TPs (TFA, PFPrA, TP182, TP348, and TP366) were identified in VUV/sulfite reaction by LCMS/MS and LCQTOF/MS. Defluorination of GenX was observed with the defluorination efficiency after 6 h reaching 17% and 67% in the VUV photolysis and VUV/sulfite reactions, respectively. Degradation mechanism for GenX based on the identified TPs and the theoretical calculation confirmed the susceptibility of GenX to nucleophilic attack. The initial reactions for GenX decomposition were C-C and C-O bond cleavage in both reactions, whereas sulfonation followed by decarboxylation was observed only in the VUV/sulfite reaction. ECOSAR ecotoxicity simulation showed that the toxicities of the TPs were not as harmful as those of GenX.
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Affiliation(s)
- Jaehee Kim
- Department of Environmental Health Sciences, School of Public Health, Seoul National University, Seoul, South Korea
| | - Taeyeon Kim
- Department of Environmental Health Sciences, School of Public Health, Seoul National University, Seoul, South Korea
| | - Heungjoo Park
- Department of Environmental Health Sciences, School of Public Health, Seoul National University, Seoul, South Korea
| | - Moon-Kyung Kim
- Institute of Health and Environment, Seoul National University, Seoul, South Korea
| | - Soyeon Eom
- Department of Environmental Health Sciences, School of Public Health, Seoul National University, Seoul, South Korea
| | - Yerin Choe
- Department of Civil and Environmental Engineering, Seoul National University, Seoul, South Korea
| | - Jong Kwon Choe
- Department of Civil and Environmental Engineering, Seoul National University, Seoul, South Korea
| | - Kyung-Duk Zoh
- Department of Environmental Health Sciences, School of Public Health, Seoul National University, Seoul, South Korea.
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Zhang C, Tang T, Knappe DRU. Oxidation of Per- and Polyfluoroalkyl Ether Acids and Other Per- and Polyfluoroalkyl Substances by Sulfate and Hydroxyl Radicals: Kinetic Insights from Experiments and Models. ENVIRONMENTAL SCIENCE & TECHNOLOGY 2023; 57:18970-18980. [PMID: 37223990 PMCID: PMC10667564 DOI: 10.1021/acs.est.3c00947] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/26/2023]
Abstract
Per- and polyfluoroalkyl substances (PFAS) are widely used anthropogenic chemicals. Because of the strength of the carbon-fluorine bond, PFAS are not destroyed in typical water treatment processes. Sulfate (SO4•-) and hydroxyl (•OH) radicals can oxidize some PFAS, but the behavior of per- and polyfluoroalkyl ether acids (PFEAs) in processes involving SO4•- and •OH is poorly understood. In this study, we determined second-order rate constants (k) describing the oxidation of 18 PFAS, including 15 novel PFEAs, by SO4•- and •OH. Among the studied PFAS, 6:2 fluorotelomer sulfonate reacted most readily with •OH [k•OH = (1.1-1.2) × 107 M-1 s-1], while polyfluoroalkyl ether acids containing an -O-CFH- moiety reacted more slowly [k•OH = (0.5-1.0) × 106 M-1 s-1]. In the presence of SO4•-, polyfluoroalkyl ether acids with an -O-CFH- moiety reacted more rapidly [kSO4•- = (0.89-4.6) × 106 M-1 s-1] than perfluoroalkyl ether carboxylic acids (PFECAs) and a chloro-perfluoro-polyether carboxylic acid (ClPFPECA) [kSO4•- = (0.85-9.5) × 104 M-1 s-1]. For homologous series of perfluoroalkyl carboxylic acids, linear and branched monoether PFECAs, and multiether PFECAs, PFAS chain length had little impact on second-order rate constants. SO4•- reacted with the carboxylic acid headgroup of perfluoroalkyl carboxylic acids and PFECAs. In contrast, for polyfluoroalkyl ether carboxylic and sulfonic acids with an -O-CFH- moiety, the site of SO4•- attack was the -O-CFH- moiety. Perfluoroalkyl ether sulfonic acids were not oxidized by SO4•- and •OH under the conditions evaluated in this study.
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Affiliation(s)
- Chuhui Zhang
- Department of Civil, Construction, and Environmental Engineering, North Carolina State University, Raleigh, North Carolina 27695, United States
| | - Tiffany Tang
- Department of Civil, Construction, and Environmental Engineering, North Carolina State University, Raleigh, North Carolina 27695, United States
| | - Detlef R U Knappe
- Department of Civil, Construction, and Environmental Engineering, North Carolina State University, Raleigh, North Carolina 27695, United States
- Center for Human Health and the Environment, North Carolina State University, Raleigh, North Carolina 27695, United States
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Zhang C, Xu Y, Liu W, Zhou H, Zhang N, Fang Z, Gao J, Sun X, Feng D, Sun X. New insights into the degradation mechanism and risk assessment of HFPO-DA by advanced oxidation processes based on activated persulfate in aqueous solutions. ECOTOXICOLOGY AND ENVIRONMENTAL SAFETY 2023; 263:115298. [PMID: 37499385 DOI: 10.1016/j.ecoenv.2023.115298] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/07/2023] [Revised: 07/09/2023] [Accepted: 07/21/2023] [Indexed: 07/29/2023]
Abstract
Hexafluoropropylene oxide dimer acid (HFPO-DA) is widely used as a substitute for perfluorooctanoic acid (PFOA). HFPO-DA exhibits high water solubility and low adsorption potential, conferring significant fluidity in aquatic environments. Given that the toxicity of HFPO-DA is similar to PFOA, it is necessary to control its content in aquatic environments. Electrochemical and thermally-activated persulfates have been successfully used to degrade HFPO-DA, but UV-activated persulfates cannot degrade the compound. Given that research on degradation mechanisms is still incomplete and lacks kinetic research, the mechanism and kinetic calculations of oxidative degradation were studied in detail using DFT calculations. And the toxicity of HFPO-DA degradation intermediates and products was evaluated to reveal the feasibility of using advanced oxidation process (AOP) technology based on persulfate to degrade HFPO-DA in wastewater. The results showed that the committed step of HFPO-DA degradation was initiated by the electron transfer reaction of SO4•- radicals. This reaction is not spontaneous at room temperature and requires sufficient electrical or thermal energy to be absorbed from the external environment. The perfluoroalcohol produced during this reaction can subsequently undergo four possible reactions: H atom abstraction from alcohol groups by an OH radical; H atom abstraction by SO4•-; direct HF removal; and HF removal with water as the catalyst. The final degradation products of HFPO-DA mainly include CO2, CF3CF2COOH, CF3COOH, FCOOH and HF, which has been identified through previous experimental analysis. Ecotoxicity assessment indicates that degradation does not produce highly toxic intermediates, and that the final products are non-toxic, supporting the feasibility of persulfate-based AOP technologies.
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Affiliation(s)
- Chenxi Zhang
- Shandong Facility Horticulture Bioengineering Research Center, Weifang University of Science and Technology, Weifang 262700, China; Environment Research Institute, Shandong University, Qingdao 266237, China
| | - Youxin Xu
- Shandong Facility Horticulture Bioengineering Research Center, Weifang University of Science and Technology, Weifang 262700, China; Environment Research Institute, Shandong University, Qingdao 266237, China
| | - Wenyan Liu
- School of agriculture, Ludong University, Yantai 264025, China
| | - Huaiyu Zhou
- Shandong Facility Horticulture Bioengineering Research Center, Weifang University of Science and Technology, Weifang 262700, China
| | - Ningning Zhang
- Shandong Facility Horticulture Bioengineering Research Center, Weifang University of Science and Technology, Weifang 262700, China
| | - Zhihao Fang
- Shandong Facility Horticulture Bioengineering Research Center, Weifang University of Science and Technology, Weifang 262700, China
| | - Junping Gao
- Shandong Facility Horticulture Bioengineering Research Center, Weifang University of Science and Technology, Weifang 262700, China
| | - Xiaoan Sun
- Shandong Facility Horticulture Bioengineering Research Center, Weifang University of Science and Technology, Weifang 262700, China
| | - Di Feng
- Shandong Facility Horticulture Bioengineering Research Center, Weifang University of Science and Technology, Weifang 262700, China.
| | - Xiaomin Sun
- Environment Research Institute, Shandong University, Qingdao 266237, China.
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Yang Z, Zhuo Q, Wang W, Guo S, Chen J, Li Y, Lv S, Yu G, Qiu Y. Fabrication and characterizations of Zn-doped SnO 2-Ti 4O 7 anode for electrochemical degradation of hexafluoropropylene oxide dimer acid and its homologues. JOURNAL OF HAZARDOUS MATERIALS 2023; 455:131605. [PMID: 37196440 DOI: 10.1016/j.jhazmat.2023.131605] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/09/2023] [Revised: 05/01/2023] [Accepted: 05/08/2023] [Indexed: 05/19/2023]
Abstract
Hexafluoropropylene oxide dimer acid (HFPO-DA) and its homologues, as perfluorinated ether alkyl substances with strong antioxidant properties, have rarely been reported by electrooxidation processes to achieve good results. Herein, we report the use of an oxygen defect stacking strategy to construct Zn-doped SnO2-Ti4O7 for the first time and enhance the electrochemical activity of Ti4O7. Compared with the original Ti4O7, the Zn-doped SnO2-Ti4O7 showed a 64.4% reduction in interfacial charge transfer resistance, a 17.5% increase in the cumulative rate of •OH generation, and an enhanced oxygen vacancy concentration. The Zn-doped SnO2-Ti4O7 anode exhibited high catalytic efficiency of 96.4% for HFPO-DA within 3.5 h at 40 mA/cm2. Hexafluoropropylene oxide trimer and tetramer acid exhibit more difficult degradation due to the protective effect of the -CF3 branched chain and the addition of the ether oxygen atom leading to a significant increase in the C-F bond dissociation energy. The degradation rates of 10 cyclic degradation experiments and the leaching concentrations of Zn and Sn after 22 electrolysis experiments demonstrated the good stability of the electrodes. In addition, the aqueous toxicity of HFPO-DA and its degradation products was evaluated. This study analyzed the electrooxidation process of HFPO-DA and its homologues for the first time, and provided some new insights.
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Affiliation(s)
- Zehong Yang
- School of Environment and Civil Engineering, Dongguan University of Technology, Dongguan 523808, Guangdong, China
| | - Qiongfang Zhuo
- School of Environment and Civil Engineering, Dongguan University of Technology, Dongguan 523808, Guangdong, China; Guangdong Provincial Key Laboratory of Environmental Pollution Control and Remediation Technology, Sun Yat-sen University, Guangzhou 510275, China; Dongguan Key Laboratory of Emerging Contaminants, Dongguan 523808, Guangdong, China.
| | - Wenlong Wang
- School of Materials Science and Engineering, Dongguan University of Technology, Dongguan 523808, Guangdong, China
| | - Shuting Guo
- School of Environment and Civil Engineering, Dongguan University of Technology, Dongguan 523808, Guangdong, China
| | - Jianfeng Chen
- School of Environment and Civil Engineering, Dongguan University of Technology, Dongguan 523808, Guangdong, China
| | - Yanliang Li
- School of Environment and Civil Engineering, Dongguan University of Technology, Dongguan 523808, Guangdong, China
| | - Sihao Lv
- School of Environment and Civil Engineering, Dongguan University of Technology, Dongguan 523808, Guangdong, China
| | - Gang Yu
- Advanced Interdisciplinary Institute of Environment and Ecology, Beijing Normal University, Zhuhai 519000, Guangdong, China
| | - Yongfu Qiu
- School of Environment and Civil Engineering, Dongguan University of Technology, Dongguan 523808, Guangdong, China
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