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Li Y, Sidikjan N, Huang L, Chen Y, Zhang Y, Li Y, Yang J, Shen G, Liu M, Huang Y. Multi-media environmental fate of polychlorinated dibenzo-p-dioxins and dibenzofurans in China: A systematic review of emissions, presence, transport modeling and health risks. ENVIRONMENTAL POLLUTION (BARKING, ESSEX : 1987) 2024; 362:124970. [PMID: 39284404 DOI: 10.1016/j.envpol.2024.124970] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/25/2024] [Revised: 09/12/2024] [Accepted: 09/13/2024] [Indexed: 09/20/2024]
Abstract
Polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans (PCDD/Fs) are notorious persistent organic pollutants (POPs) with proven toxicity to human and ecosystems. This review critically evaluates existing research, emphasizing knowledge gaps regarding PCDD/F emissions, environmental behavior, human exposure, and associated risks in China. The current emission inventory of PCDD/Fs in China remains highly uncertain, both in terms of total emissions and emission trends. Moreover, existing monitoring data primarily focus on areas near pollution sources, limiting comprehensive understanding of the overall spatiotemporal characteristics of PCDD/F pollution. To address this, we propose a novel approach that integrates the Multi-media Urban Mode (MUM) model with an atmospheric chemical transport model that includes a dual adsorption model to capture gas-particle partitioning of PCDD/Fs in the atmosphere. This coupled model can simulate the transport and fate of PCDD/Fs in multi-media environments with high spatiotemporal resolution, facilitating a nuanced understanding of the impacts of emissions, climate, urbanization and other factors on PCDD/F pollution. Additionally, dietary ingestion, particularly from animal-derived foods, is identified as the predominant source (up to 98%) of human exposure to PCDD/Fs. While the changes in dietary structure, population distribution, and age structure can influence human exposure to PCDD/Fs, their impacts have not yet been quantified. The proposed model lays the foundation for a systematic assessment of health risks from PCDD/F exposure through various pathways by further incorporating a food chain model. Overall, this review offers a comprehensive strategy for assessing PCDD/F pollution, encompassing the entire continuum from emissions to environmental impacts.
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Affiliation(s)
- Ying Li
- Key Laboratory of Geographic Information Science (Ministry of Education), School of Geographical Sciences, East China Normal University, 200241, Shanghai, China
| | - Nazupar Sidikjan
- Key Laboratory of Geographic Information Science (Ministry of Education), School of Geographical Sciences, East China Normal University, 200241, Shanghai, China
| | - Lin Huang
- Key Laboratory of Geographic Information Science (Ministry of Education), School of Geographical Sciences, East China Normal University, 200241, Shanghai, China
| | - Yangmin Chen
- Key Laboratory of Geographic Information Science (Ministry of Education), School of Geographical Sciences, East China Normal University, 200241, Shanghai, China
| | - Yunshan Zhang
- Key Laboratory of Geographic Information Science (Ministry of Education), School of Geographical Sciences, East China Normal University, 200241, Shanghai, China
| | - Ye Li
- Key Laboratory of Geographic Information Science (Ministry of Education), School of Geographical Sciences, East China Normal University, 200241, Shanghai, China
| | - Jing Yang
- Key Laboratory of Geographic Information Science (Ministry of Education), School of Geographical Sciences, East China Normal University, 200241, Shanghai, China
| | - Guofeng Shen
- Laboratory of Earth Surface Processes, College of Urban and Environmental Science, Peking University, Beijing, 100871, China
| | - Min Liu
- Key Laboratory of Geographic Information Science (Ministry of Education), School of Geographical Sciences, East China Normal University, 200241, Shanghai, China
| | - Ye Huang
- Key Laboratory of Geographic Information Science (Ministry of Education), School of Geographical Sciences, East China Normal University, 200241, Shanghai, China.
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Zhang H, Xie K, Luo Q, Tang J, Zhang YN. Prediction of Base-Catalyzed Hydrolysis Kinetics of Polychlorinated Dibenzo- p-Dioxins by Density Functional Theory Calculations. ENVIRONMENTAL SCIENCE & TECHNOLOGY 2024; 58:5483-5490. [PMID: 38484382 DOI: 10.1021/acs.est.3c08985] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 03/27/2024]
Abstract
Polychlorinated dibenzo-p-dioxins (PCDDs), comprising 75 congeners, have gained considerable attention from the general public and the scientific community owing to their high toxic potential. The base-catalyzed hydrolysis of PCDDs is crucial for the assessment of their environmental persistence. Nonetheless, owing to the substantial number of congeners and low hydrolysis rates of PCDDs, conducting hydrolysis experiments proves to be exceedingly time-consuming and financially burdensome. Herein, density functional theory and transition state theory were employed to predict the base-catalyzed hydrolysis of PCDDs in aquatic environments. Findings reveal that PCDDs undergo base-catalyzed hydrolysis in aquatic environments with two competing pathways: prevailing dioxin ring-opening and reduced reactivity in the hydrolytic dechlorination pathway. The resultant minor products include hydroxylated PCDDs, which exhibit thermodynamic stability surpassing that of the principal product, chlorinated hydroxydiphenyl ethers. The half-lives (ranging from 17.10 to 1.33 × 1010 h at pH = 8) associated with the base-catalyzed hydrolysis of PCDDs dissolved in water were shorter compared to those within the water-sediment environmental system. This observation implies that hydroxide ions can protect aquatic environments from PCDD contamination. Notably, this study represents the first attempt to predict the base-catalyzed hydrolysis of PCDDs by using quantum chemical methods.
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Affiliation(s)
- Haiqin Zhang
- College of Environmental Science and Engineering, Liaoning Technical University, Fuxin 123000, China
- Key Laboratory of Regional Environment and Eco-Remediation of Ministry of Education, College of Environment, Shenyang University, Shenyang 110000, China
| | - Kun Xie
- College of Environmental Science and Engineering, Liaoning Technical University, Fuxin 123000, China
| | - Qing Luo
- Key Laboratory of Regional Environment and Eco-Remediation of Ministry of Education, College of Environment, Shenyang University, Shenyang 110000, China
| | - Jiaxi Tang
- College of Environmental Science and Engineering, Liaoning Technical University, Fuxin 123000, China
| | - Ya-Nan Zhang
- School of Environment, Northeast Normal University, Changchun 130117, China
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Liao Z, Zeng M, Wang L. Atmospheric oxidation mechansim of polychlorinated biphenyls (PCBs) initiated by OH radicals. CHEMOSPHERE 2020; 240:124756. [PMID: 31563106 DOI: 10.1016/j.chemosphere.2019.124756] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/25/2019] [Revised: 09/03/2019] [Accepted: 09/03/2019] [Indexed: 05/16/2023]
Abstract
Long-range atmospheric transport (LRAT) is the main route for circulating polychlorinated biphenyls (PCBs) from sources to sinks. In the atmosphere, PCBs containing six and less chlorine substitutions exist mainly as vapour, which can be oxidized by OH radical. Here, using quantum chemistry and transition state theory, we calculated the rate coefficients for reactions of OH radical with selected PCBs. The predicted rate coefficients agree with the available experimental values within a factor of 3. Calculations show that all PCBs considered here are persistent with their half-lives longer than 24 h. Reactions of PCBs with OH radical start with OH addition to the phenyl rings, forming PCB-n-OH adducts. Fate of biphenyl-n-OH (BP-n-OH, n = 2, 3, 4) adducts in the atmosphere is investigated. Calculations show that these radical adducts react similarly to benzene-OH adducts, forming hydroxybiphenyl (HO-BP) as main product and bicyclic radicals as minor products in their reaction with O2. Effective rates of reaction with O2 in the atmosphere are relatively slow, ∼1400, ∼45000, and ∼800 s-1 for BP-2-OH, BP-3-OH, and BP-4-OH, respectively. This suggests considerable reactions between BP-n-OH adducts and NO2, forming nitrobiphenyls. The bicyclic radicals from BP-n-OH + O2 would further transform to highly oxidized products as observed in a previous study. PCB-OH adducts react similarly as BP-n-OH radicals. For the three PCB-OH radicals considered here, their reactions with O2 also form HO-PCBs and bicyclic radicals.
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Affiliation(s)
- Zhihong Liao
- School of Chemistry & Chemical Engineering, South China University of Technology, Guangzhou, 510640, China
| | - Min Zeng
- School of Chemistry & Chemical Engineering, South China University of Technology, Guangzhou, 510640, China
| | - Liming Wang
- School of Chemistry & Chemical Engineering, South China University of Technology, Guangzhou, 510640, China; Guangdong Provincial Key Laboratory of Atmospheric Environment and Pollution Control, South China University of Technology, Guangzhou, 510006, China.
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Xiaolan Zeng, Sun X, Wang H. Computational Study on the Atmospheric Oxidation Mechanism of 6-Chlorobenzo[a]pyrene Initiated by OH Radicals. RUSSIAN JOURNAL OF PHYSICAL CHEMISTRY A 2019. [DOI: 10.1134/s0036024419130363] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
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Rashidian N, Zahedi E, Shiroudi A. Kinetic and mechanistic insight into the OH-initiated atmospheric oxidation of 2,3,7,8-tetrachlorodibenzo-p-dioxin via OH-addition and hydrogen abstraction pathways: A theoretical investigation. THE SCIENCE OF THE TOTAL ENVIRONMENT 2019; 679:106-114. [PMID: 31082585 DOI: 10.1016/j.scitotenv.2019.05.056] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/13/2019] [Revised: 05/03/2019] [Accepted: 05/05/2019] [Indexed: 06/09/2023]
Abstract
The 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) is the most toxic polychlorinated dibenzo-p-dioxin. The OH-initiated oxidation of TCDD has been studied using the density functional, canonical transition state, and canonical Rice-Ramsperger-Kassel-Marcus theories. The kinetic data were corrected for quantum tunneling by the Wigner and Eckart models. All OH addition and hydrogen atom abstraction channels were thermodynamically exergonic. The kinetic and thermodynamic data analysis at the reliable level MPWB1K/MG3S//M06-2X/MG3S indicate that the addition of OH to the carbon atom adjacent to the oxygen atom in dioxin ring leads to the formation of predominant adduct. The calculated bimolecular rate constant for the formation of predominant adduct was ~5.97-6.75 × 10-13 cm3 molecule-1 s-1, its branching ratio was ~0.955, and the overall rate constant for the OH-initiated oxidation of TCDD was ~6.25-7.08 × 10-13 cm3 molecule-1 s-1. The atmospheric lifetime of TCDD determined by OH was ~8.17-9.26 days indicating the TCDD can be categorized as medium lifetime organic pollutant.
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Affiliation(s)
- Nooshin Rashidian
- Department of Chemistry, Shahrood Branch, Islamic Azad University, Shahrood, Iran
| | - Ehsan Zahedi
- Department of Chemistry, Shahrood Branch, Islamic Azad University, Shahrood, Iran.
| | - Abolfazl Shiroudi
- Young Researchers and Elite Club, East Tehran Branch, Islamic Azad University, Tehran, Iran
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Zeng X, Wang Y. Computational investigation of the atmospheric oxidation reactions of polybrominated dibenzo-p-dioxins initiated by OH radicals. CHEMOSPHERE 2018; 212:548-553. [PMID: 30165281 DOI: 10.1016/j.chemosphere.2018.08.116] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/16/2018] [Revised: 07/30/2018] [Accepted: 08/23/2018] [Indexed: 06/08/2023]
Abstract
Density functional theory (DFT) method was used to study OH-initiated atmospheric oxidative reactions of some polybrominated dibenzo-p-dioxins (PBDDs). B3LYP functional and 6-311++G (2df,p) basis set were applied to optimize molecular structures of all stationary points involved in the investigated reactions. The rate constants for key elementary reactions were estimated by means of transition state theory. The computational results demonstrate that all addition reactions of PBDDs with OH radicals can occur spontaneously at standard conditions, however, the OH addition reactions are very slow due to low atmospheric concentration of OH radicals. Addition reactions occurring at γ-C position dominate in OH addition of all PBDDs. With the number of bromine atoms substituting at α-sites increases, the overall rate coefficients of OH addition decrease. The succeeding addition reactions of PBDD-OH adducts with O2 take place hardly both thermodynamically and kinetically. Abstraction reaction of H atoms by O2 is a governing route for PBDD-α(β)-adducts without bromine atoms at the same site, while the fused-ring CO bond fission is a main reaction channel for PBDD-γ-adducts, which will produce substituted phenoxy radicals.
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Affiliation(s)
- Xiaolan Zeng
- College of Chemistry and Chemical Engineering, Xinyang Normal University, Henan Xinyang 464000, China.
| | - Yan Wang
- College of Chemistry and Chemical Engineering, Xinyang Normal University, Henan Xinyang 464000, China
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7
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Wang Y, Zeng X. OH-initiated atmospheric oxidation mechanism of 1-chloropyrene: A theoretical study. COMPUT THEOR CHEM 2017. [DOI: 10.1016/j.comptc.2017.06.011] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/19/2022]
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8
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Xin ML, Yang JW, Li Y. The mechanism for enhanced oxidation degradation of dioxin-like PCBs (PCB-77) in the atmosphere by the solvation effect. Chem Cent J 2017; 11:61. [PMID: 29086899 PMCID: PMC5503851 DOI: 10.1186/s13065-017-0291-3] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/16/2017] [Accepted: 07/05/2017] [Indexed: 11/29/2022] Open
Abstract
The reaction pathways of PCB-77 in the atmosphere with ·OH, O2, NOx, and 1O2 were inferred based on density functional theory calculations with the 6-31G* basis set. The structures the reactants, transition states, intermediates, and products were optimized. The energy barriers and reaction heats were obtained to determine the energetically favorable reaction pathways. To study the solvation effect, the energy barriers and reaction rates for PCB-77 with different polar and nonpolar solvents (cyclohexane, benzene, carbon tetrachloride, chloroform, acetone, dichloromethane, ethanol, methanol, acetonitrile, dimethylsulfoxide, and water) were calculated. The results showed that ·OH preferentially added to the C5 atom of PCB-77, which has no Cl atom substituent, to generate the intermediate IM5. This intermediate subsequently reacted with O2 via pathway A to generate IM5a, with an energy barrier of 7.27 kcal/mol and total reaction rate of 8.45 × 10−8 cm3/molecule s. Pathway B involved direct dehydrogenation of IM5 to produce the OH-PCBs intermediate IM5b, with an energy barrier of 28.49 kcal/mol and total reaction rate of 1.15 × 10−5 cm3/molecule s. The most likely degradation pathway of PCB-77 in the atmosphere is pathway A to produce IM5a. The solvation effect results showed that cyclohexane, carbon tetrachloride, and benzene could reduce the reaction energy barrier of pathway A. Among these solvents, the solvation effect of benzene was the largest, and could reduce the total reaction energy barrier by 25%. Cyclohexane, carbon tetrachloride, benzene, dichloromethane, acetone, and ethanol could increase the total reaction rate of pathway A. The increase in the reaction rate of pathway A with benzene was 8%. The effect of solvents on oxidative degradation of PCB-77 in the atmosphere is important.The reaction pathways of PCB-77 in the atmosphere with •OH, O2, NOx, and 1O2 were inferred based on density functional theory calculations with the 6-31G* basis set. Different polar and nonpolar solvents: cyclohexane, benzene, carbon tetrachloride, chloroform, acetone, dichloromethane, ethanol, methanol, acetonitrile, dimethylsulfoxide, and water were selected to study the solvation effect on the favorable reaction pathways. The investigated results showed what kind of pathway was most likely to occur and the solvent effect on the reaction pathway ![]()
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Affiliation(s)
- Mei-Ling Xin
- College of Environmental Science and Engineering, North China Electric Power University, No. 2, Beinong Road, Beijing, 102206, China.,The Moe Key Laboratory of Resources and Environmental Systems Optimization, North China Electric Power University, Beijing, 102206, China
| | - Jia-Wen Yang
- College of Environmental Science and Engineering, North China Electric Power University, No. 2, Beinong Road, Beijing, 102206, China.,The Moe Key Laboratory of Resources and Environmental Systems Optimization, North China Electric Power University, Beijing, 102206, China
| | - Yu Li
- College of Environmental Science and Engineering, North China Electric Power University, No. 2, Beinong Road, Beijing, 102206, China. .,The Moe Key Laboratory of Resources and Environmental Systems Optimization, North China Electric Power University, Beijing, 102206, China.
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9
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Zeng X, Chen J, Qu R, Pan X, Wang Z. The OH-initiated atmospheric chemical reactions of polyfluorinated dibenzofurans and polychlorinated dibenzofurans: A comparative theoretical study. CHEMOSPHERE 2017; 168:10-17. [PMID: 27776226 DOI: 10.1016/j.chemosphere.2016.10.062] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/11/2016] [Revised: 10/16/2016] [Accepted: 10/18/2016] [Indexed: 06/06/2023]
Abstract
The atmospheric chemical reactions of some polyfluorinated dibenzofurans (PFDFs) and polychlorinated dibenzofurans (PCDFs), initiated by OH radical, were investigated by performing theoretical calculations using density functional theory (DFT) and B3LYP/6-311++G(2df,p) method. The obtained results indicate that OH addition reactions of PFDFs and PCDFs occurring at C1∼4 and CA sites are thermodynamic spontaneous changes and the branching ratio of the PF(C)DF-OH adducts is decided primarily by kinetic factor. The OH addition reactions of PFDFs taking place at fluorinated C1∼4 positions are kinetically comparable with those occurring at nonfluorinated C1∼4 positions, while OH addition reactions of PCDFs occurring at chlorinated C1∼4 sites are negligible. The total rate constants of the addition reactions of PFDFs or PCDFs become smaller with consecutive fluorination or chlorination, and substituting at C1 position has more adverse effects than substitution at other sites. The succedent O2 addition reactions of PF(C)DF-OH adducts are thermodynamic nonspontaneous processes under the atmospheric conditions, and have high Gibbs free energies of activation (ΔrG≠). The substituted dibenzofuranols are the primary oxidation products for PCDFs under the atmospheric conditions. However, other oxidative products may also be available for PFDFs besides substituted dibenzofuranols.
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Affiliation(s)
- Xiaolan Zeng
- State Key Laboratory of Pollution Control and Resources Reuse, School of the Environment, Nanjing University, Nanjing, 210023, China; College of Chemistry and Chemical Engineering, Xinyang Normal University, Henan, Xinyang, 464000, China
| | - Jing Chen
- State Key Laboratory of Pollution Control and Resources Reuse, School of the Environment, Nanjing University, Nanjing, 210023, China
| | - Ruijuan Qu
- State Key Laboratory of Pollution Control and Resources Reuse, School of the Environment, Nanjing University, Nanjing, 210023, China
| | - Xiaoxue Pan
- State Key Laboratory of Pollution Control and Resources Reuse, School of the Environment, Nanjing University, Nanjing, 210023, China
| | - Zunyao Wang
- State Key Laboratory of Pollution Control and Resources Reuse, School of the Environment, Nanjing University, Nanjing, 210023, China.
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Gao HY, Mao L, Shao B, Huang CH, Zhu BZ. Why Does 2,3,5,6-Tetrachlorophenol Generate the Strongest Intrinsic Chemiluminescence among All Nineteen Chlorophenolic Persistent Organic Pollutants during Environmentally-friendly Advanced Oxidation Process? Sci Rep 2016; 6:33159. [PMID: 27748358 PMCID: PMC5066286 DOI: 10.1038/srep33159] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/23/2016] [Accepted: 05/17/2016] [Indexed: 12/04/2022] Open
Abstract
We found recently that intrinsic chemiluminescence (CL) could be produced by all 19 chlorophenolic persistent organic pollutants during environmentally-friendly advanced oxidation processes. Interestingly and unexpectedly, the strongest CL was produced not by the most-highly chlorinated pentachlorophenol (PCP), but rather by the less chlorinated 2,3,5,6-tetrachlorophenol (2,3,5,6-TeCP), one of the three tetrachlorophenol (TeCPs) isomers. However, it remains unclear what is the underlying molecular mechanism. Here we show that not only chlorinated quinoid intermediates, but more interestingly, semiquinone radicals were produced during the degradation of the three TeCPs and PCP by Fenton reagents, and the type and yield of which were found to be well correlated with CL generation. We propose that hydroxyl radical-dependent formation of more tetrachlorinated quinoids, quinone-dioxetanes and electronically excited carbonyl species might be responsible for the exceptionally strong CL production by 2,3,5,6-TeCP as compared to PCP and its two isomers. This is the first report showing the critical role of quinoid intermediates and semiquinone radicals in CL generation from polychlorinated phenols and Fenton system. These new findings may have broad chemical and environmental implications for future studies on remediation of other halogenated persistent aromatic pollutants by advanced oxidation processes.
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Affiliation(s)
- Hui-Ying Gao
- State Key Laboratory of Environmental Chemistry and Ecotoxicology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, P. R. China
- University of Chinese Academy of Sciences, Beijing 100049, P. R. China
| | - Li Mao
- State Key Laboratory of Environmental Chemistry and Ecotoxicology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, P. R. China
- University of Chinese Academy of Sciences, Beijing 100049, P. R. China
| | - Bo Shao
- State Key Laboratory of Environmental Chemistry and Ecotoxicology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, P. R. China
- University of Chinese Academy of Sciences, Beijing 100049, P. R. China
| | - Chun-Hua Huang
- State Key Laboratory of Environmental Chemistry and Ecotoxicology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, P. R. China
- University of Chinese Academy of Sciences, Beijing 100049, P. R. China
| | - Ben-Zhan Zhu
- State Key Laboratory of Environmental Chemistry and Ecotoxicology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, P. R. China
- University of Chinese Academy of Sciences, Beijing 100049, P. R. China
- Linus Pauling Institute, Oregon State University, Corvallis, OR 97331, USA
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11
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Gerasimov G. Modeling study of polychlorinated dibenzo-p-dioxins and dibenzofurans behavior in flue gases under electron beam irradiation. CHEMOSPHERE 2016; 158:100-106. [PMID: 27258900 DOI: 10.1016/j.chemosphere.2016.05.064] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/18/2016] [Revised: 05/08/2016] [Accepted: 05/22/2016] [Indexed: 06/05/2023]
Abstract
The efficiency of the electron beam treatment of industrial flue gases for the removal of sulfur and nitrogen oxides was investigated as applied to polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) using methods of mathematical modeling. The proposed kinetic model of the process includes mechanism of PCDD/Fs decomposition caused by their interaction with OH radicals generated in the flue gases under the electron beam (EB) irradiation as well as PCDD/Fs formation from unburned aromatic compounds. The model allows to predict the main features of the process, which are observed in pilot plant installations, as well as to evaluate the process efficiency. The results of calculations are compared with the available experimental data.
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Affiliation(s)
- Gennady Gerasimov
- Institute of Mechanics, Moscow State University, 1 Michurinsky Ave., 119192, Moscow, Russia.
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12
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Zeng X, Zhang X, Wang Z. Theoretical study on the OH-initiated oxidation mechanism of polyfluorinated dibenzo-p-dioxins under the atmospheric conditions. CHEMOSPHERE 2016; 144:2036-2043. [PMID: 26580719 DOI: 10.1016/j.chemosphere.2015.10.106] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/04/2015] [Revised: 10/23/2015] [Accepted: 10/25/2015] [Indexed: 06/05/2023]
Abstract
Density functional theory (DFT) calculations at the B3LYP/6-311++G(2df,p) level of theory have been carried out to investigate the atmospheric oxidation mechanisms of some polyfluorinated dibenzo-p-dioxins (PFDDs), initiated by OH radical. The computed results show that all OH addition reactions of PFDDs are thermodynamically spontaneous processes and the branch ratio of the PFDD-OH adducts is determined by the magnitude of the Gibbs free energies of activation (Δ(r)G(≠)) and hence rate constants (k) for addition reactions. The OH reactions with all studied PFDDs are dominated by Cγ-addition and the total rate constants for OH addition decrease with increasing the number of fluorine atom substituting at α positions. Under the atmospheric conditions, the subsequent O2 addition reactions of PFDD-OH adducts occur hardly thermodynamically and are slow kinetically. For PFDD-α(β)-OH adducts without F atom at same positions the main reaction pathway is H abstraction by O2, while PFDD-γ-OH adducts will undergo fused-ring C-O bond cleavage, affording the substituted phenoxy radicals.
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Affiliation(s)
- Xiaolan Zeng
- State Key Laboratory of Pollution Control and Resources Reuse, School of the Environment, Nanjing University, Nanjing 210023, China; College of Chemistry and Chemical Engineering, Xinyang Normal University, Henan, Xinyang 464000, China
| | - Xiaoling Zhang
- State Key Laboratory of Pollution Control and Resources Reuse, School of the Environment, Nanjing University, Nanjing 210023, China
| | - Zunyao Wang
- State Key Laboratory of Pollution Control and Resources Reuse, School of the Environment, Nanjing University, Nanjing 210023, China.
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Quantitative Structure-Activity Relationships Study on the Rate Constants of Polychlorinated Dibenzo-p-Dioxins with OH Radical. Int J Mol Sci 2015; 16:18812-24. [PMID: 26274950 PMCID: PMC4581273 DOI: 10.3390/ijms160818812] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/06/2015] [Revised: 07/30/2015] [Accepted: 08/04/2015] [Indexed: 01/15/2023] Open
Abstract
The OH-initiated reaction rate constants (kOH) are of great importance to measure atmospheric behaviors of polychlorinated dibenzo-p-dioxins (PCDDs) in the environment. The rate constants of 75 PCDDs with the OH radical at 298.15 K have been calculated using high level molecular orbital theory, and the rate constants (kα, kβ, kγ and kOH) were further analyzed by the quantitative structure-activity relationships (QSAR) study. According to the QSAR models, the relations between rate constants and the numbers and positions of Cl atoms, the energy of the highest occupied molecular orbital (EHOMO), the energy of the lowest unoccupied molecular orbital (ELUMO), the difference ΔEHOMO-LUMO between EHOMO and ELUMO, and the dipole of oxidizing agents (D) were discussed. It was found that EHOMO is the main factor in the kOH. The number of Cl atoms is more effective than the number of relative position of these Cl atoms in the kOH. The kOH decreases with the increase of the substitute number of Cl atoms.
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14
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Zhang K, Sun S, Zhang H. Mechanism and kinetic study on the ring-opening degradation of 2,3,7,8-tetrachlorinated dibenzofuran initiated by OH radicals in waste incineration. RSC Adv 2015. [DOI: 10.1039/c5ra13804c] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
This work is about bimolecular reactions and subsequent unimolecular reactions including the ring-opening and hydrogen-transfer of 2,3,7,8-TCDF-OH adducts.
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Affiliation(s)
- Kun Zhang
- College of Chemical and Environmental Engineering
- Harbin University of Science and Technology
- Harbin 150080
- P. R. China
| | - Shengmin Sun
- College of Food Engineering
- Harbin University of Commerce
- Harbin 150076
- P. R. China
| | - Hui Zhang
- College of Chemical and Environmental Engineering
- Harbin University of Science and Technology
- Harbin 150080
- P. R. China
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15
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Vallejo M, Fresnedo San Román M, Ortiz I, Irabien A. Overview of the PCDD/Fs degradation potential and formation risk in the application of advanced oxidation processes (AOPs) to wastewater treatment. CHEMOSPHERE 2015; 118:44-56. [PMID: 24974140 DOI: 10.1016/j.chemosphere.2014.05.077] [Citation(s) in RCA: 54] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/08/2014] [Revised: 05/23/2014] [Accepted: 05/26/2014] [Indexed: 06/03/2023]
Abstract
Polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) are a family of unintentionally produced persistent organic pollutants (POPs) that have received considerable public and scientific attention due to the toxicity of some of their congeners, more specifically those with chlorine substitution in the 2,3,7,8 positions. The environmental management and control of PCDD/Fs is addressed at a global level through the Stockholm Convention that establishes that POPs should be destroyed or irreversibly transformed in order to reduce or eliminate their release to the environment. Several technologies, including advanced oxidation processes (AOPs) such as photolysis, photocatalysis and Fenton oxidation, have been considered as effective methods for destroying PCDD/Fs in polluted waters. Nevertheless, during the remediation of wastewaters it is critical that the treatment technologies applied do not lead to the formation of by-products that are themselves POPs, especially if PCDD/Fs precursors or chlorine are present in the reaction medium. Despite the high effectiveness of AOPs in the oxidation of major contaminants, scarce references deal with the monitoring of PCDD/Fs in the course of the oxidation process, revealing that a detailed assessment of non-combustion technologies with respect to PCDD/Fs formation is still lacking. This study reports a review of the state of the art related to the potential remediation and/or formation of PCDD/Fs as a result of the application of AOPs for the treatment of polluted waters, warning on the correct selection of the operating conditions.
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Affiliation(s)
- Marta Vallejo
- Departamento de Ingenierías Química y Biomolecular, ETSIIyT, Universidad de Cantabria, Avda. de los Castros, 39005 Santander, Spain
| | - M Fresnedo San Román
- Departamento de Ingenierías Química y Biomolecular, ETSIIyT, Universidad de Cantabria, Avda. de los Castros, 39005 Santander, Spain
| | - Inmaculada Ortiz
- Departamento de Ingenierías Química y Biomolecular, ETSIIyT, Universidad de Cantabria, Avda. de los Castros, 39005 Santander, Spain.
| | - Angel Irabien
- Departamento de Ingenierías Química y Biomolecular, ETSIIyT, Universidad de Cantabria, Avda. de los Castros, 39005 Santander, Spain
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16
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Li P, Wang W, Sun Q, Li Z, Du A, Bi S, Zhao Y. Insights into the Mechanism of the Reaction between Tetrachloro‐
p‐
Benzoquinone and Hydrogen Peroxide and their Implications in the Catalytic Role of Water Molecules in Producing the Hydroxyl Radial. Chemphyschem 2013; 14:2737-43. [PMID: 23893963 DOI: 10.1002/cphc.201300395] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/20/2013] [Revised: 05/07/2013] [Indexed: 11/06/2022]
Affiliation(s)
- Ping Li
- Key Laboratory of Life‐Organic Analysis, School of Chemistry and Chemical Engineering, Qufu Normal University, Qufu, 273165 (P. R. China)
| | - Weihua Wang
- Key Laboratory of Life‐Organic Analysis, School of Chemistry and Chemical Engineering, Qufu Normal University, Qufu, 273165 (P. R. China)
| | - Qiao Sun
- Australian Institute for Bioengineering and Nanotechnology, University of Queensland, QLD 4072 (Australia)
| | - Zhen Li
- Institute of Superconducting and Electronic Materials, University of Wollongong, NSW 2500 (Australia)
| | - Aijun Du
- School of Chemistry, Physics and Mechanical Engineering, Queensland University of Technology, Brisbane, QLD 4001 (Australia)
| | - Siwei Bi
- Key Laboratory of Life‐Organic Analysis, School of Chemistry and Chemical Engineering, Qufu Normal University, Qufu, 273165 (P. R. China)
| | - Yan Zhao
- Key Laboratory of Life‐Organic Analysis, School of Chemistry and Chemical Engineering, Qufu Normal University, Qufu, 273165 (P. R. China)
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17
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Wang L, Tang A. The oxidation mechanism of polychlorinated dibenzo-p-dioxins under the atmospheric conditions - a theoretical study. CHEMOSPHERE 2012; 89:950-956. [PMID: 22835868 DOI: 10.1016/j.chemosphere.2012.06.050] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/13/2011] [Revised: 05/22/2012] [Accepted: 06/30/2012] [Indexed: 06/01/2023]
Abstract
The atmospheric polychlorinated dibenzo-p-dioxins (PCDDs) partition appreciably in the gas phase, where they undergo rapid oxidation. The atmospheric oxidation mechanisms of a few PCDDs, initiated by OH radical, are studied using density functional theory calculations. The oxidations start with OH-addition to the aromatic rings, dominantly at γ-sites, followed by the non-chlorinated β-sites; while additions to the α-sites or chlorinated sites are negligible. For PCDDs with all β-sites being chlorinated, formation of PCDD-γ-OH adducts become virtually the only reaction path. Under the atmospheric conditions, the PCDD-β/γ-OH adducts combine with O(2) slowly at rates <1s(-1). Instead, the PCDD-β-OH adducts will react with O(2) through hydrogen abstraction at rates <50s(-1), forming PCDD-β-ol, and the PCDD-γ-OH adducts will decompose to the substituted phenoxy radicals by fused-ring C-O bond cleavage at rates of 10(3) ~10(5) s(-1). The reaction mechanisms of PCDDs are drastically different from the peroxy mechanism for the atmospheric oxidations of benzene and dibenzofuran.
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Affiliation(s)
- Liming Wang
- School of Chemistry & Chemical Engineering, South China University of Technology, Guangzhou 510640, China.
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18
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Theoretical studies on the interaction mechanisms between tetrachloro-p-benzoquinone and hydrogen peroxide. Struct Chem 2012. [DOI: 10.1007/s11224-012-0155-3] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
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19
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Zhang C, Zhao Y, Bai J, Gong C, Sun X. Mechanism and kinetic study on the OH-initiated degradation of 2,3,7,8-tetrachlorinated dibenzofuran in atmosphere. THE SCIENCE OF THE TOTAL ENVIRONMENT 2012; 435-436:53-60. [PMID: 22846763 DOI: 10.1016/j.scitotenv.2012.07.007] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/14/2011] [Revised: 07/01/2012] [Accepted: 07/01/2012] [Indexed: 06/01/2023]
Abstract
High-accuracy molecular orbital calculation has been performed to investigate the atmospheric oxidation reaction of 2,3,7,8-tetrachlorodibenzofuran (2,3,7,8-TeCDF) initiated by the OH radical in the presence of O(2) and NO/H(2)O. The possible channels involved in the reaction are discussed, and the favorable reaction pathways are revealed. The degradation occurs easily once the OH radical initiates the reaction. Two aspects need to be mentioned: one is that H(2)O in atmosphere is a source of OH radical which will initiate a new round of degradation and improve the degradation efficiency; the other is that the furan ring of 2,3,7,8-TeCDF can be turned into dioxin ring, which may explain the experimental hypothesis that polychlorodibenzofurans can be transformed to polychlorodibenzo-p-dioxins. Rate constants of the elementary reactions are calculated over a temperature range of 250-400K. Arrhenius formulas are fitted and the atmospheric lifetimes of reaction species in the troposphere are discussed for the first time, which can be applied to the study on the model simulation and the management of the hazardous materials.
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Affiliation(s)
- Chenxi Zhang
- Environment Research Institute, Shandong University, Jinan 250100, PR China
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20
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Zhang C, Sun T, Sun X. Mechanism for OH-initiated degradation of 2,3,7,8-tetrachlorinated dibenzo-p-dioxins in the presence of O2 and NO/H2O. ENVIRONMENTAL SCIENCE & TECHNOLOGY 2011; 45:4756-4762. [PMID: 21539348 DOI: 10.1021/es104271a] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/30/2023]
Abstract
The atmospheric oxidation of 2,3,7,8-tetrachlorodibenzo-p-dioxin (2,3,7,8-TeCDD) is investigated theoretically by high-accuracy molecular orbital calculation. The study shows that the OH radical can easily be added to the C atom adjacent to the O atom in dioxin ring to form OH radical adduct. The 2,3,7,8-TeCDD-OH adduct can immediately react with O(2) to form the 2,3,7,8-TeCDD-OH-O(2) adduct which can react with NO or H(2)O to complete the decomposition process. The degradation mechanism varies with the addition position of O(2) and the O-abstraction by NO. The OH radical can be reproduced through the H-abstraction of H(2)O and initiate a new round of degradation. The direct dynamic calculation is performed, and the rate constants is calculated over a temperature range of 200-1200 K, using the canonical variational transition state theory with small-curvature tunneling effect. The four-parameter formula of rate constants with the temperature is fitted and the lifetimes of the reaction species in the troposphere are estimated according to the rate constants, which is helpful for the atmospheric model study on the formation and degradation of dioxin.
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Affiliation(s)
- Chenxi Zhang
- Environment Research Institute, Shandong University, Jinan 250100, PR China
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Wang L, Tang A. Atmospheric oxidation mechanisms of polychlorinated dibenzo-p-dioxins are different from those of benzene and dibenzofuran: a theoretical prediction. CHEMOSPHERE 2011; 82:782-785. [PMID: 21109286 DOI: 10.1016/j.chemosphere.2010.11.006] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/21/2010] [Revised: 10/18/2010] [Accepted: 11/01/2010] [Indexed: 05/30/2023]
Abstract
The reaction mechanisms of dibenzo-p-dioxin (DD) and 2,3,7,8-TCDD with OH radical have been studied using density functional theory calculations. Under the atmospheric conditions, ca 42% of DD+OH reaction proceeds as formation of DD-OH-β adduct, which will react with O(2) slowly; while the rest will proceed as formation of DD-OH-γ adduct, which will decompose to the substituted phenoxy radical P1 by the fused-ring C-O bond cleavage. For 2,3,7,8-TCDD+OH, the reaction will predominantly form the substituted phenoxy radical P2. The reaction mechanisms are drastically different from the peroxy mechanism for the atmospheric oxidations of benzene and dibenzofuran.
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Affiliation(s)
- Liming Wang
- School of Chemistry and Chemical Engineering, South China University of Technology, Guangzhou 510640, China.
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22
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Hung PC, Chang SH, Chi KH, Chang MB. Degradation of gaseous dioxin-like compounds with dielectric barrier discharges. JOURNAL OF HAZARDOUS MATERIALS 2010; 182:246-251. [PMID: 20605067 DOI: 10.1016/j.jhazmat.2010.06.021] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/21/2010] [Revised: 06/03/2010] [Accepted: 06/07/2010] [Indexed: 05/29/2023]
Abstract
Developing effective technologies to reduce dioxin emissions has become an important issue in the research and industrial fields. In this study, a dioxin-containing gas stream generating system was applied to evaluate the effectiveness of dielectric barrier discharge (DBD) plasma technology for the destruction of dioxin-like compounds. The results indicate that the destruction efficiencies of dioxin-like compounds achieved with DBD plasma strongly depend on the composition of the simulated gas stream. As the DBD plasma is operated with the simulated gas stream containing 20% water vapor, around 74% PCDDs and 89% PCDFs can be destroyed by DBD plasma. UV, electrons, and OH radicals are generated via the DBD plasma process and react with the dioxin-like compounds in the gas stream. Dechlorination via UV and electrons and decomposition via OH radicals occur at the same time and significantly increase the destruction efficiency of PCDD/Fs in the presence of oxygen and water vapor. Additionally, the total toxicity destruction of dioxin-like compounds with the input energy of 1 kJ increases from 1.47 to 3.06 ng-TEQ(WHO) as the water vapor is incorporated into the gas stream.
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Affiliation(s)
- Pao Chen Hung
- Graduate Institute of Environmental Engineering, National Central University, Chungli 320, Taiwan
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23
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Estimating persistence of brominated and chlorinated organic pollutants in air, water, soil, and sediments with the QSPR-based classification scheme. Mol Divers 2010; 15:173-88. [PMID: 20386980 DOI: 10.1007/s11030-010-9250-9] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/12/2009] [Accepted: 03/22/2010] [Indexed: 10/19/2022]
Abstract
We have estimated degradation half-lives of both brominated and chlorinated dibenzo-p-dioxins (PBDDs and PCDDs), furans (PBDFs and PCDFs), biphenyls (PBBs and PCBs), naphthalenes (PBNs and PCNs), diphenyl ethers (PBDEs and PCDEs) as well as selected unsubstituted polycyclic aromatic hydrocarbons (PAHs) in air, surface water, surface soil, and sediments (in total of 1,431 compounds in four compartments). Next, we compared the persistence between chloro- (relatively well-studied) and bromo- (less studied) analogs. The predictions have been performed based on the quantitative structure-property relationship (QSPR) scheme with use of k-nearest neighbors (kNN) classifier and the semi-quantitative system of persistence classes. The classification models utilized principal components derived from the principal component analysis of a set of 24 constitutional and quantum mechanical descriptors as input variables. Accuracies of classification (based on an external validation) were 86, 85, 87, and 75% for air, surface water, surface soil, and sediments, respectively. The persistence of all chlorinated species increased with increasing halogenation degree. In the case of brominated organic pollutants (Br-OPs), the trend was the same for air and sediments. However, we noticed that the opposite trend for persistence in surface water and soil. The results suggest that, due to high photoreactivity of C-Br chemical bonds, photolytic processes occurring in surface water and soil are able to play significant role in transforming and removing Br-OPs from these compartments. This contribution is the first attempt of classifying together Br-OPs and Cl-OPs according to their persistence, in particular, environmental compartments.
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Altarawneh M, Kennedy EM, Dlugogorski BZ, Mackie JC. Computational Study of the Oxidation and Decomposition of Dibenzofuran under Atmospheric Conditions. J Phys Chem A 2008; 112:6960-7. [DOI: 10.1021/jp800093j] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Mohammednoor Altarawneh
- Process Safety and Environment Protection Research Group, School of Engineering, The University of Newcastle, Callaghan, NSW 2308, Australia
| | - Eric M. Kennedy
- Process Safety and Environment Protection Research Group, School of Engineering, The University of Newcastle, Callaghan, NSW 2308, Australia
| | - Bogdan Z. Dlugogorski
- Process Safety and Environment Protection Research Group, School of Engineering, The University of Newcastle, Callaghan, NSW 2308, Australia
| | - John C. Mackie
- Process Safety and Environment Protection Research Group, School of Engineering, The University of Newcastle, Callaghan, NSW 2308, Australia
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25
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Altarawneh M, Dlugogorski BZ, Kennedy EM, Mackie JC. Quantum Chemical and Kinetic Study of Formation of 2-Chlorophenoxy Radical from 2-Chlorophenol: Unimolecular Decomposition and Bimolecular Reactions with H, OH, Cl, and O2. J Phys Chem A 2008; 112:3680-92. [DOI: 10.1021/jp712168n] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
Affiliation(s)
- Mohammednoor Altarawneh
- Process Safety and Environment Protection Research Group, School of Engineering, The University of Newcastle, Callaghan, NSW 2308, Australia
| | - Bogdan Z. Dlugogorski
- Process Safety and Environment Protection Research Group, School of Engineering, The University of Newcastle, Callaghan, NSW 2308, Australia
| | - Eric M. Kennedy
- Process Safety and Environment Protection Research Group, School of Engineering, The University of Newcastle, Callaghan, NSW 2308, Australia
| | - John C. Mackie
- Process Safety and Environment Protection Research Group, School of Engineering, The University of Newcastle, Callaghan, NSW 2308, Australia
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26
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27
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Catalytic Conversions of Polychlorinated Benzenes and Dioxins with Low-chlorine Using V2O5/TiO2. Catal Letters 2007. [DOI: 10.1007/s10562-007-9283-6] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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28
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Suárez E, Suárez D, Menéndez MI, López R, Sordo TL. Formation of trichlorinated dibenzo-p-dioxins from 2,4-dichlorophenol and 2,4,5-trichlorophenolate: a theoretical study. Chemphyschem 2006; 7:2331-8. [PMID: 17086592 DOI: 10.1002/cphc.200600355] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
The reaction of the 2,4,5-trichlorophenolate anion with 2,4-dichlorophenol to afford trichlorinated dibenzo-p-dioxins (T3CDDs) is investigated at the B3LYP/6-31+G(d) and B3LYP/6-311+G(3df,2p)//B3LYP/6-31+G(d)+ZPVE(B3LYP/6-31+G(d)) levels of theory. The first stage of the process corresponds to the formation of a predioxin, which can evolve through four different routes. Two of them lead directly to the products 2,3,7-T3CDD and 1,3,8-T3CDD, and the other two afford different predioxin-type intermediates, which in turn can evolve through all or some of the four routes to give new predioxins or T3CDD. Consequently, the theoretical results obtained show plainly the complex chemistry implied in the formation of dioxins from chlorophenols via anionic mechanisms by disclosing all the critical structures through which the system evolves, thus allowing assessment of the viability of the different mechanistic routes and the accessible products. The statistical thermodynamics treatment at 1 atm and 298.15, 600, 900, and 1200 K indicates that at higher temperatures, the Gibbs energy barrier for the formation of the initial predioxin is clearly the rate-determining step for the whole process, but at lower temperatures the Gibbs energy barrier for this step is similar to those for its evolution into 2,3,7-T3CDD. This result is in contrast with previous proposals that the closure of the central ring is the rate-limiting step. Finally, according to our results the rate constant for the formation of polychlorinated dibenzo-p-dioxins increases with the temperature, in agreement with the experimental observation that the conversion of trichlorophenols increases when going from 600 to 900 K in the gas phase in the absence of catalysts, and with DFT molecular dynamics results.
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Affiliation(s)
- Ernesto Suárez
- Departamento de Química Física y Analítica, Facultad de Química, Universidad de Oviedo, C/Julián Clavería 8, 33006 Oviedo, Principado de Asturias, Spain
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29
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Li XD, Zhang J, Yan JH, Chen T, Lu SY, Cen KF. Effect of water on catalyzed de novo formation of polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans. JOURNAL OF HAZARDOUS MATERIALS 2006; 137:57-61. [PMID: 16533559 DOI: 10.1016/j.jhazmat.2006.01.068] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/11/2005] [Revised: 01/31/2006] [Accepted: 01/31/2006] [Indexed: 05/07/2023]
Abstract
The effect of water vapor on catalyzed de novo formation of polychlorinated dibenzo-p-dioxins (PCDD) and polychlorinated dibenzofurans (PCDF) was investigated through experiments conducted on a fixed-bed apparatus. The results indicated that water vapor could promote the formation of PCDD and PCDF. The dominant pathway was activating fly ash in this work, while water also reacted with chlorine to change the equilibrium of Deacon reaction, which influenced the final yield of PCDD/PCDF. Also a suppression effect of water on CuCl(2) was found according to the values of the catalysis indicator. It is possible that water reduced the catalysis of CuCl(2) or prevented its direct chlorination. But the overall effect of water on the formation of PCDD and PCDF was promotion rather than inhibition.
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Affiliation(s)
- Xiao-dong Li
- State Key Laboratory of Clean Energy Utilization, Zhejiang University, 310027 Zhejiang, PR China.
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Katsumata H, Kaneco S, Suzuki T, Ohta K, Yobiko Y. Degradation of polychlorinated dibenzo-p-dioxins in aqueous solution by Fe(II)/H2O2/UV system. CHEMOSPHERE 2006; 63:592-9. [PMID: 16213552 DOI: 10.1016/j.chemosphere.2005.08.015] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/15/2005] [Revised: 08/04/2005] [Accepted: 08/12/2005] [Indexed: 05/04/2023]
Abstract
The photodegradation of polychlorinated dibenzo-p-dioxins (PCDDs), which include tetra- to octa-CDDs (TeCDD, PeCDD, HxCDD, HpCDD and OCDD), was carried out in the presence of Fe(II) and H2O2 mixed reagent. The degradation efficiency was strongly influenced by UV irradiation, and the initial concentrations of H2O2 and Fe(II). An initial TeCDD concentration of 10 ng l(-1) was completely degraded within 20 min under the optimum conditions. All PCDDs tested were successfully degraded by Fe(II)/H2O2/UV treatment and complete degradation of TeCDD, PeCDD and HxCDD was achieved within 120 min. PCDD photodegradation rates decreased with the number of chlorine atoms. The degradation process of TeCDD by this system seems to be initiated by an oxidative reaction (OH* radical attack) because less chlorinated DDs as intermediate products were not detected. From the Frontier electron density calculation, the first OH* radical attack positions on TeCDD were found to be four C atoms neighboring two O atoms. The decomposition of TeCDD gave 4,5-dichlorocatechol as an intermediate product. A TeCDD degradation scheme was proposed based on the identified intermediate and the values of Frontier electron density. Based on these results, Fe(II)/H2O2/UV system could be useful technology for the treatment of wastewater containing persistent pollutants such as dioxins and polychlorinated biphenyls.
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Affiliation(s)
- Hideyuki Katsumata
- Sattelite Venture Business Laboratory, Mie University, Tsu, Mie 514-8507, Japan.
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31
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Ljubić I, Sabljić A. Theoretical Study of Structure, Vibrational Frequencies, and Electronic Spectra of Polychlorinated Dibenzo-p-dioxins. J Phys Chem A 2006; 110:4524-34. [PMID: 16571059 DOI: 10.1021/jp056013m] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The structure, vibrational frequencies, and excited states of 2,3,7,8-tetrachloro-, 1,4,6,9-tetrachloro-, and octachlorodibenzo-p-dioxin (2,3,7,8-TCDD, 1,4,6,9-TCDD, and OCDD) were studied via complete active space SCF followed by the multireference second-order perturbative approach (CASSCF/CASPT2), as well as the time-dependent density functional theory (TD-B3LYP). The cc-pVDZ basis set and the full pi-electron active spaces of 16 electrons in 14 active orbitals were employed. Whereas 2,3,7,8-TCDD assumes a planar D(2)(h)() minimum, 1,4,6,9-TCDD and OCDD are slightly folded exhibiting the C(2)(v)() symmetry. The extra stabilization due to the folding is very small. In all three isomers the highly intensive band system in the 200-240 nm region is dominated by the transitions to the 2(1)B(2u) and 3(1)B(2u) states with by far the largest oscillator strengths. The low-intensity absorptions in the 280-320 nm region can be attributed to the 1(1)B(2u) <-- 1(1)A(g), with possible contribution of the vibronically allowed 2(1)A(g) <-- 1(1)A(g) transition. Both CASPT2 and TD-B3LYP convincingly predict 1(3)B(3g) to be the lowest lying triplet state, which contradicts the experimental assignments. Calculated harmonic wavenumbers and absorption spectra agree well with the experimental data, and are sufficiently distinct to allow for an unambiguous identification of the three isomers.
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Affiliation(s)
- Ivan Ljubić
- Department of Physical Chemistry, Ruder Bosković Institute, P.O. Box 180, HR-10002, Zagreb, Republic of Croatia.
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Ljubić I, Sabljić A. Dibenzo-p-dioxin. An ab Initio CASSCF/CASPT2 Study of the π−π* and n−π* Valence Excited States. J Phys Chem A 2005; 109:8209-17. [PMID: 16834207 DOI: 10.1021/jp051867s] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The pi-pi* and n-pi* valence excited states of dibenzo-p-dioxin (DD) were studied via the complete active space SCF and multiconfigurational second-order perturbation theory employing the cc-pVDZ basis set and the full pi-electron active spaces of 16 electrons in 14 active orbitals. The geometry and harmonic vibrational wavenumbers of the ground state correlate well with the experimental and other theoretical data. In particular, significant improvements over previously reported theoretical results are observed for the excitation energies. All of the pi-pi* excited states exhibit planar D(2h)minima. Thus no evidence was found for a C(2v) butterfly-like relaxation, although the wavenumbers of the b(3u) butterfly flapping mode proved exceedingly low in both the ground S(0)((1)A(g)) and the lowest dipole allowed excited S(1)((1)B(2u)) state. The calculations of oscillator strengths established the 2(1)B(2u) <-- 1(1)A(g) and 2(1)B(1u) <-- 1(1)A(g) transitions as by far the most intense, whereas the only allowed of the n-pi* transitions ((1)B(3u)) should possess only a modest intensity. Studies into dependence of the oscillator strengths on the extent of the butterfly-like folding showed that the electronic spectrum is more consistent with a folded equilibrium geometry assumed by DD in solution.
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Affiliation(s)
- Ivan Ljubić
- Department of Physical Chemistry, Ruer Bosković Institute, P.O. Box 180, HR-10002 Zagreb, Republic of Croatia.
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Chu SZ, Inoue S, Wada K, Li D, Suzuki J. Fabrication and photocatalytic characterizations of ordered nanoporous X-doped (X = N, C, S, Ru, Te, and Si) TiO2/Al2O3 films on ITO/glass. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2005; 21:8035-41. [PMID: 16089417 DOI: 10.1021/la050902j] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/03/2023]
Abstract
Transparent, ordered nanoporous TiO2/Al2O3 composite films doped with metal elements (Ru, Si, and Te) and nonmetal elements (N, C, and S) were fabricated by successive anodization and sol-gel process directly on glass substrates covered with a tin-doped indium oxide (ITO) film. The doping of ruthenium, nitrogen, carbon, and sulfur in TiO2 exhibited an enhanced effect on the absorbance, while the doping of silicon and tellurium showed little effect. Particularly, the N- and Ru-doped TiO2/Al2O3 films on ITO/glass developed an enhanced absorption red shift of 580 nm (-N) and 500 nm (-Ru). The nanoporous TiO2/Al2O3 composite film exhibited the highest photocatalytic activity in decomposing acetaldehyde under ultraviolet-light irradiation, with a value of 13 times in initial reaction rate or 7.8 times in quantum yield higher than a commercially available TiO2 material, Degussa P25. The ultraviolet-light photocatalytic activities of nanoporous TiO2/Al2O3 films were enhanced by the doping of nitrogen, carbon, and sulfur but slightly weakened by the doping of ruthenium, silicon, and tellurium. Particularly, the nanoporous N-doped TiO2/Al2O3 films exhibited effective photocatalytic activity on ultraviolet light decomposition of a highly toxic dioxin, HpCDD, and gave the highest decomposition rate of approximately 95% (via 7 h of irradiation) for the specimen with a dopant content of 1.7 wt % nitrogen.
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Affiliation(s)
- Song-Zhu Chu
- Advanced Materials Laboratory, National Institute for Materials Science (NIMS), Namiki 1-1, Tsukuba, Ibaraki 305-0044, Japan.
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