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Pan W, He S, Xue Q, Liu X, Fu J, Xiao K, Zhang A. First-principles study on the heterogeneous formation of environmentally persistent free radicals (EPFRs) over α-Fe 2O 3(0001) surface: Effect of oxygen vacancy. J Environ Sci (China) 2024; 142:279-289. [PMID: 38527893 DOI: 10.1016/j.jes.2023.07.021] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/19/2023] [Revised: 07/13/2023] [Accepted: 07/19/2023] [Indexed: 03/27/2024]
Abstract
Metal oxides with oxygen vacancies have a significant impact on catalytic activity for the transformation of organic pollutants in waste-to-energy (WtE) incineration processes. This study aims to investigate the influence of hematite surface oxygen point defects on the formation of environmentally persistent free radicals (EPFRs) from phenolic compounds based on the first-principles calculations. Two oxygen-deficient conditions were considered: oxygen vacancies at the top surface and on the subsurface. Our simulations indicate that the adsorption strength of phenol on the α-Fe2O3(0001) surface is enhanced by the presence of oxygen vacancies. However, the presence of oxygen vacancies has a negative impact on the dissociation of the phenol molecule, particularly for the surface with a defective point at the top layer. Thermo-kinetic parameters were established over a temperature range of 300-1000 K, and lower reaction rate constants were observed for the scission of phenolic O-H bonds over the oxygen-deficient surfaces compared to the pristine surface. The negative effects caused by the oxygen-deficient conditions could be attributed to the local reduction of FeIII to FeII, which lower the oxidizing ability of surface reaction sites. The findings of this study provide us a promising approach to regulate the formation of EPFRs.
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Affiliation(s)
- Wenxiao Pan
- State Key Laboratory of Environmental Chemistry and Ecotoxicology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China
| | - Shuming He
- School of Environment, Hangzhou Institute for Advanced Study, University of Chinese Academy of Sciences, Hangzhou 310012, China
| | - Qiao Xue
- State Key Laboratory of Environmental Chemistry and Ecotoxicology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China.
| | - Xian Liu
- State Key Laboratory of Environmental Chemistry and Ecotoxicology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China
| | - Jianjie Fu
- State Key Laboratory of Environmental Chemistry and Ecotoxicology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China; School of Environment, Hangzhou Institute for Advanced Study, University of Chinese Academy of Sciences, Hangzhou 310012, China
| | - Kang Xiao
- College of Resources and Environment, University of Chinese Academy of Sciences, Beijing 100049, China; Beijing Yanshan Earth Critical Zone National Research Station, University of Chinese Academy of Sciences, Beijing 101408, China
| | - Aiqian Zhang
- State Key Laboratory of Environmental Chemistry and Ecotoxicology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China; School of Environment, Hangzhou Institute for Advanced Study, University of Chinese Academy of Sciences, Hangzhou 310012, China; College of Resources and Environment, University of Chinese Academy of Sciences, Beijing 100049, China.
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Ahmed SM, Oumnov RA, Kizilkaya O, Hall RW, Sprunger PT, Cook RL. Role of Electronegativity in Environmentally Persistent Free Radicals (EPFRs) Formation on ZnO. THE JOURNAL OF PHYSICAL CHEMISTRY. C, NANOMATERIALS AND INTERFACES 2024; 128:5179-5188. [PMID: 38567373 PMCID: PMC10983065 DOI: 10.1021/acs.jpcc.3c08231] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 12/17/2023] [Revised: 02/28/2024] [Accepted: 03/04/2024] [Indexed: 04/04/2024]
Abstract
Environmentally persistent free radicals (EPFRs), a group of emerging pollutants, have significantly longer lifetimes than typical free radicals. EPFRs form by the adsorption of organic precursors on a transition metal oxide (TMO) surface involving electron charge transfer between the organic and TMO. In this paper, dihalogenated benzenes were incorporated to study the role of electronegativity in the electron transfer process to obtain a fundamental knowledge of EPFR formation mechanism on ZnO. Upon chemisorption on ZnO nanoparticles at 250 °C, electron paramagnetic resonance (EPR) confirms the formation of oxygen adjacent carbon-centered organic free radicals with concentrations between 1016 and 1017 spins/g. The radical concentrations show a trend of 1,2-dibromobenzene (DBB) > 1,2-dichlorobenzene (DCB) > 1,2-difluorobenzene (DFB) illustrating the role of electronegativity on the amount of radical formation. X-ray absorption spectroscopy (XAS) confirms the reduction of the Zn2+ metal center, contrasting previous experimental evidence of an oxidative mechanism for ZnO single crystal EPFR formation. The extent of Zn reduction for the different organics (DBB > DCB > DFB) also correlates to their polarity. DFT calculations provide theoretical evidence of ZnO surface reduction and exhibit a similar trend of degree of reduction for different organics, further building on the experimental findings. The lifetimes of the EPFRs formed confirm a noteworthy persistency.
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Affiliation(s)
- Syed Monjur Ahmed
- Department
of Chemistry, Louisiana State University, Baton Rouge, Louisiana 70803, United States
| | - Reuben A. Oumnov
- Department
of Natural Sciences and Mathematics, Dominican
University of California, San Rafael, California 94901, United States
| | - Orhan Kizilkaya
- Center for
Advanced Microstructures and Devices, Louisiana
State University, 6980
Jefferson Highway, Baton Rouge, Louisiana 70806, United States
| | - Randall W. Hall
- Department
of Natural Sciences and Mathematics, Dominican
University of California, San Rafael, California 94901, United States
| | - Phillip T. Sprunger
- Center for
Advanced Microstructures and Devices, Louisiana
State University, 6980
Jefferson Highway, Baton Rouge, Louisiana 70806, United States
- Department
of Physics and Astronomy, Louisiana State
University, Baton Rouge, Louisiana 70803, United States
| | - Robert L. Cook
- Department
of Chemistry, Louisiana State University, Baton Rouge, Louisiana 70803, United States
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Khachatryan L, Rezk MY, Nde D, Hasan F, Lomnicki S, Boldor D, Cook R, Sprunger P, Hall R, Cormier S. New Features of Laboratory-Generated EPFRs from 1,2-Dichlorobenzene (DCB) and 2-Monochlorophenol (MCP). ACS OMEGA 2024; 9:9226-9235. [PMID: 38434874 PMCID: PMC10905596 DOI: 10.1021/acsomega.3c08271] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 10/20/2023] [Revised: 12/18/2023] [Accepted: 01/22/2024] [Indexed: 03/05/2024]
Abstract
The present research is primarily focused on investigating the characteristics of environmentally persistent free radicals (EPFRs) generated from commonly recognized aromatic precursors, namely, 1,2-dichlorobenzene (DCB) and 2-monochlorophenol (MCP), within controlled laboratory conditions at a temperature of 230 °C, termed as DCB230 and MCP230 EPFRs, respectively. An intriguing observation has emerged during the creation of EPFRs from MCP and DCB utilizing a catalyst 5% CuO/SiO2, which was prepared through various methods. A previously proposed mechanism, advanced by Dellinger and colleagues (a conventional model), postulated a positive correlation between the degree of hydroxylation on the catalyst's surface (higher hydroxylated, HH and less hydroxylated, LH) and the anticipated EPFR yields. In the present study, this correlation was specifically confirmed for the DCB precursor. Particularly, it was observed that increasing the degree of hydroxylation at the catalyst's surface resulted in a greater yield of EPFRs for DCB230. The unexpected finding was the indifferent behavior of MCP230 EPFRs to the surface morphology of the catalyst, i.e., no matter whether copper oxide nanoparticles are distributed densely, sparsely, or completely agglomerated. The yields of MCP230 EPFRs remained consistent regardless of the catalyst type or preparation protocol. Although current experimental results confirm the early model for the generation of DCB EPFRs (i.e., the higher the hydroxylation is, the higher the yield of EPFRs), it is of utmost importance to closely explore the heterogeneous alternative mechanism(s) responsible for generating MCP230 EPFRs, which may run parallel to the conventional model. In this study, detailed spectral analysis was conducted using the EPR technique to examine the nature of DCB230 EPFRs and the aging phenomenon of DCB230 EPFRs while they exist as surface-bound o-semiquinone radicals (o-SQ) on copper sites. Various aspects concerning bound radicals were explored, including the hydrogen-bonding tendencies of o-semiquinone (o-SQ) radicals, the potential reversibility of hydroxylation processes occurring on the catalyst's surface, and the analysis of selected EPR spectra using EasySpin MATLAB. Furthermore, alternative routes for EPFR generation were thoroughly discussed and compared with the conventional model.
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Affiliation(s)
- Lavrent Khachatryan
- Department
of Chemistry, Louisiana State University, Baton Rouge, Louisiana 70803, United States
| | - Marwan Y. Rezk
- Department
of Engineering Science, Biological Engineering, Louisiana State University, Baton Rouge, Louisiana 70803, United States
| | - Divine Nde
- Department
of Chemistry, Louisiana State University, Baton Rouge, Louisiana 70803, United States
| | - Farhana Hasan
- Department
of Environmental Sciences, Louisiana State
University, Baton
Rouge, Louisiana 70803, United States
| | - Slawomir Lomnicki
- Department
of Environmental Sciences, Louisiana State
University, Baton
Rouge, Louisiana 70803, United States
| | - Dorin Boldor
- Department
of Engineering Science, Biological Engineering, Louisiana State University, Baton Rouge, Louisiana 70803, United States
| | - Robert Cook
- Department
of Chemistry, Louisiana State University, Baton Rouge, Louisiana 70803, United States
| | - Phillip Sprunger
- Department
of Physics and Astronomy, Louisiana State
University, Baton
Rouge, Louisiana 70803, United States
| | - Randall Hall
- Natural
Sciences and Mathematics, School of Health and Natural Sciences, Dominican University of California, San Rafael, California 94901, United States
| | - Stephania Cormier
- Department
of Biological Sciences, LSU Superfund Research
Program and Pennington Biomedical Research Center, Baton Rouge, Louisiana 70808, United States
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Xu Y, Lu X, Su G, Chen X, Meng J, Li Q, Wang C, Shi B. Scientific and regulatory challenges of environmentally persistent free radicals: From formation theory to risk prevention strategies. JOURNAL OF HAZARDOUS MATERIALS 2023; 456:131674. [PMID: 37236112 DOI: 10.1016/j.jhazmat.2023.131674] [Citation(s) in RCA: 10] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/19/2023] [Revised: 05/18/2023] [Accepted: 05/20/2023] [Indexed: 05/28/2023]
Abstract
EPFRs (Environmentally Persistent Free Radicals) are a class of pollutants that have been identified as potential environmental contaminants due to their persistence and ability to generate reactive oxygen species (ROS) that can cause oxidative stress in living organisms. However, no study has comprehensively summarized the production conditions, influencing factors and toxic mechanisms of EPFRs, impeding exposure toxicity assessments and risk prevention strategies. To bridge the gap between theoretical research and practical application, a thorough literature review to summarize the formation, environmental effects, and biotoxicity of EPFRs are conducted. A total of 470 relevant papers were screened in Web of Science Core collection databases. The transfer of electrons between interfaces and the cleavage of covalent bonds of persistent organic pollutants is crucial to the generation of EPFRs, which is induced by external sources of energy, including thermal energy, light energy, transition metal ions, and others. In the thermal system, the stable covalent bond of organic matter can be destroyed by heat energy at low temperature to form EPFRs, while the formed EPFRs can be destroyed at high temperature. Light can also accelerate the production of free radicals and promote the degradation of organic matter. The persistence and stability of EPFRs are synergistically influenced by individual environmental factors such as environmental humidity, oxygen content, organic matter content, and environmental pH. Studying the formation mechanism of EPFRs and their biotoxicity is essential for fully understanding the hazards posed by these emerging environmental contaminants.
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Affiliation(s)
- Yulin Xu
- School of Municipal and Environmental Engineering, Shenyang Jianzhu University, Shenyang 110168, China; Key Laboratory of Environmental Nanotechnology and Health Effects Research, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China
| | - Xiaofei Lu
- School of Municipal and Environmental Engineering, Shenyang Jianzhu University, Shenyang 110168, China
| | - Guijin Su
- Key Laboratory of Environmental Nanotechnology and Health Effects Research, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China; University of Chinese Academy of Sciences, Beijing 100049, China
| | - Xing Chen
- School of Municipal and Environmental Engineering, Shenyang Jianzhu University, Shenyang 110168, China; Key Laboratory of Environmental Nanotechnology and Health Effects Research, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China
| | - Jing Meng
- Key Laboratory of Environmental Nanotechnology and Health Effects Research, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China; University of Chinese Academy of Sciences, Beijing 100049, China
| | - Qianqian Li
- Key Laboratory of Environmental Nanotechnology and Health Effects Research, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China; University of Chinese Academy of Sciences, Beijing 100049, China
| | - Chenxi Wang
- School of Municipal and Environmental Engineering, Shenyang Jianzhu University, Shenyang 110168, China; Key Laboratory of Environmental Nanotechnology and Health Effects Research, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China
| | - Bin Shi
- Key Laboratory of Environmental Nanotechnology and Health Effects Research, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China; University of Chinese Academy of Sciences, Beijing 100049, China.
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