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Heqing Tang - One of the best experts on this subject based on the ideXlab platform.
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Complete Debromination of 2,2′,4,4′-tetrabromodiphenyl ether by visible-light photocatalysis on g-C3N4 supported Pd
Applied Catalysis B: Environmental, 2020Co-Authors: Ming Lei, Zhiying Wang, Lihua Zhu, Wenshan Nie, Heqing TangAbstract:Abstract Deep Debromination of polybrominated diphenyl ethers (PBDEs) by visible light photocatalysis is still a challenge in the field of halogenated pollutants control. Here, an efficient photocatalyst (Pd/g-C3N4) was prepared by a simple impregnation-chemical reduction method with bulk g-C3N4 and PdCl2 as precursors. Under preferred reaction conditions (visible light irradiation for 120 min), the use of the 0.5% Pd/g-C3N4 composites (0.4 g L−1) yielded an almost complete Debromination of BDE47 (10 μmol L−1) in methanol-water mixture, while the Debromination of BDE47 did not occur on pure g-C3N4. A “Pd-promoted active H atom species attack and C-Br bond cleavage” route was proposed according to the identified degradation intermediates. A catalytic mechanism was further clarified: Pd nanoparticles exerted affinity interaction with bromine atoms, and the storing of electrons on Pd would increase the binding interaction. In the Debromination process, methanol acts as both a hole scavenger and a hydrogen donor to provide active H atom species through the reaction of H+ and photogenerated electrons on Pd nanoparticles. The initiation of BDE47 Debromination on Pd nanoparticles required an induction period to enrich a critical amount of electrons for stretching the C-Br bond and its subsequent being attacked by active H atoms. The generated 2,2′-dibromodiphenyl ether (BDE4) would be further reduced to bromine-free products by hydro-Debromination process or coupling reaction.
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Peculiar and full Debromination of tetrabromodiphenyl ether on Pd/TiO2: A competing route through hydro-Debromination and coupling-Debromination
Applied Catalysis B: Environmental, 2020Co-Authors: Ming Lei, Zhiying Wang, Lihua Zhu, Yao Tang, Huimin Wang, Heqing TangAbstract:Abstract The use of palladium deposited TiO2 (Pd/TiO2) as catalysts yielded complete Debromination of 2,2′,4,4′-tetrabromodiphenyl ether (BDE47) in isopropanol solution containing NaOH at 40 °C within 60 min. The final organic products were diphenyl ether and dibenzofuran. It was disclosed that two competing reduction paths (hydro-Debromination and coupling-Debromination) occurred over Pd nanoparticles. The hydro-Debromination was dependent on the participation of active H atom species generated by catalytic transfer hydrogenation on metallic Pd. The coupling-Debromination proceeded via the oxidative addition of Pd(0) to B r 2 C 12 H 8 OB r 2 ′ , leading to an transition state of B r 2 Pd II C 12 H 8 OB r 2 ′ , the reductive dissociation of which resulted in the elimination of Br− ions, producing a new transition state Pd 0 C 12 H 8 OB r 2 ′ − . A further oxidative addition of Pd 0 C 12 H 8 OB r 2 ′ − generated B r 2 ′ Pd II C 12 H 8 O − , and its final reductive elimination provided dibenzofuran, leading to the regeneration of Pd(0). The integration of the catalytic coupling and hydrogenation reaction on Pd nanoparticles greatly accelerated the removal of the halogenated organic pollutants.
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Reductive Debromination of Polybrominated Diphenyl Ethers: Dependence on Br Number of the Br-Rich Phenyl Ring.
Environmental science & technology, 2019Co-Authors: Shun Guo, Ming Lei, Lihua Zhu, Tetsuro Majima, Heqing TangAbstract:Reductive Debromination has been widely studied for the degradation of polybrominated diphenyl ethers (PBDEs), although the reaction mechanisms are not so clear. In the present study, the photocatalytic degradation and Debromination of ten PBDEs were carried out with CuO/TiO2 nanocomposites as the photocatalyst under an anaerobic condition. The pseudo-first-order rate constants were obtained for the photocatalytic Debromination of PBDEs, and their relative rate constants ( kR) were evaluated against kR= 1 for BDE209. Unlike the generally accepted summary that kR is dependent on the total Br number ( N) of PBDEs, kR is found to depend on the Br number on a phenyl ring with more Br atoms than the other one. In other words, a phenyl ring substituted by more Br is more reactive for the reductive Debromination. The calculated LUMO energies ( ELUMO) of all PBDEs are well correlated to the more reactive phenyl ring with more Br, compared with the N of two phenyl rings. The result was explained by LUMO localization on the Br-rich phenyl ring, suggesting that the reductive Debromination occurs on the phenyl ring.
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Reductive Debromination of Polybrominated Diphenyl Ethers: Dependence on Br Number of the Br-Rich Phenyl Ring
2019Co-Authors: Shun Guo, Ming Lei, Lihua Zhu, Tetsuro Majima, Heqing TangAbstract:Reductive Debromination has been widely studied for the degradation of polybrominated diphenyl ethers (PBDEs), although the reaction mechanisms are not so clear. In the present study, the photocatalytic degradation and Debromination of ten PBDEs were carried out with CuO/TiO2 nanocomposites as the photocatalyst under an anaerobic condition. The pseudo-first-order rate constants were obtained for the photocatalytic Debromination of PBDEs, and their relative rate constants (kR) were evaluated against kR= 1 for BDE209. Unlike the generally accepted summary that kR is dependent on the total Br number (N) of PBDEs, kR is found to depend on the Br number on a phenyl ring with more Br atoms than the other one. In other words, a phenyl ring substituted by more Br is more reactive for the reductive Debromination. The calculated LUMO energies (ELUMO) of all PBDEs are well correlated to the more reactive phenyl ring with more Br, compared with the N of two phenyl rings. The result was explained by LUMO localization on the Br-rich phenyl ring, suggesting that the reductive Debromination occurs on the phenyl ring
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Ultrarapid and Deep Debromination of Tetrabromodiphenyl Ether over Noble-Metal-Free Cu/TiO2 Nanocomposites under Mild Conditions.
Environmental science & technology, 2018Co-Authors: Ming Lei, Shun Guo, Zhiying Wang, Lihua Zhu, Heqing TangAbstract:Fast and deep Debromination of polybrominated diphenyl ethers (PBDEs) under mild conditions is a challenge in the field of pollution control. A strategy was developed to achieve it by exploiting Cu/TiO2 composites as a noble-metal-free catalyst. Toward the Debromination of 2,2′,4,4′-tetrabromodiphenyl ether (BDE47) as a typical PBDE, the use of Cu/TiO2 as a catalyst and hydrazine hydrate (N2H4·H2O) as a reducing agent yielded a degradation removal of 100% and a Debromination efficiency of 87.7% in 3 s. A complete Debromination of BDE47 at 1500 mg L–1 was possible by successively adding N2H4·H2O. A Debromination pathway involving active H atom species was proposed for the catalytic transfer hydrogenation (CTH) of PBDEs according to the identified degradation intermediates. A mechanism was further clarified by density functional theory calculations: electrons are delivered from N2H4·H2O to the metallic Cu atom via a coordination of N in N2H4·H2O with Cu atoms. The electron-trapped Cu atom interacts with ads...
Thies Thiemann - One of the best experts on this subject based on the ideXlab platform.
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Zn dust mediated reductive Debromination of tetrabromobisphenol A (TBBPA).
Journal of hazardous materials, 2009Co-Authors: Guo-bin Liu, Hong-yun Zhao, Thies ThiemannAbstract:Zinc dust/sodium hydroxide/ammonium formate system is highly effective for the Debromination of the ubiquitous pollutant tetrabromobisphenol A (TBPPA) to bisphenol A (BPA). Treatment of pure TBPPA with NaOH or with another alkali hydroxide in the presence of ammonium formate in an alcohol at elevated temperatures (78-116 degrees C) leads to a successful Debromination. An almost quantitative removal of TBBPA can be achieved.
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Zn dust mediated reductive Debromination of tetrabromobisphenol A (TBBPA).
Journal of Hazardous Materials, 2009Co-Authors: Guo-bin Liu, Hong-yun Zhao, Thies ThiemannAbstract:Abstract Zinc dust/sodium hydroxide/ammonium formate system is highly effective for the Debromination of the ubiquitous pollutant tetrabromobisphenol A (TBPPA) to bisphenol A (BPA). Treatment of pure TBPPA with NaOH or with another alkali hydroxide in the presence of ammonium formate in an alcohol at elevated temperatures (78–116 °C) leads to a successful Debromination. An almost quantitative removal of TBBPA can be achieved.
Hua Yin - One of the best experts on this subject based on the ideXlab platform.
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rapid Debromination of polybrominated diphenyl ethers pbdes by zero valent metal and bimetals mechanisms and pathways assisted by density function theory calculation
Environmental Pollution, 2018Co-Authors: Rui Wang, Ting Tang, Kaibo Huang, Hua Yin, Zhang Lin, Zhi DangAbstract:Polybrominated diphenyl ethers (PBDEs) undergo Debromination when they were exposed in zerovalent metal or bimetallic systems. Yet their Debromination pathways and mechanisms in these systems were not well understood. Here we reported the Debromination pathways of three BDE congeners (BDE-21, 25 and 29) by nano-zerovalent iron (n-ZVI). All these BDE congeners have three bromine substituents that were located in ortho-, meta- and para-positions. Results demonstrated that BDE-21, 25 and 29 preferentially debrominate meta-, ortho- and para-bromines, respectively, suggesting that bromine substituent at each position (i.e. ortho-, meta- or para-) of PBDEs can be preferentially removed. Singly occupied molecular orbitals of BDE anions are well correlated with their actual Debromination pathways, which successfully explain why these BDE congeners exhibit certain Debromination pathways in n-ZVI system. In addition, microscale zerovalent zinc (m-ZVZ), iron-based bimetals (Fe/Ag and Fe/Pd) were also used to debrominate PBDEs, with BDE-21 as target pollutant. We found that the Debromination pathways of BDE-21 in m-ZVZ and Fe/Ag systems are the same to those in n-ZVI system, but were partially different from those in Fe/Pd systems. The Debromination of BDE-21 in Pd-H2 system as well as the solvent kinetic isotope effect in single metal and bimetallic systems suggests that H atom transfer is the dominant mechanism in Fe/Pd system, while e-transfer is still the dominant mechanism in Fe/Ag system.
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Experimental and theoretical investigations on Debromination pathways of polybrominated biphenyls (PBBs) under ultraviolet light.
Chemosphere, 2018Co-Authors: Rui Wang, Ting Tang, Siyuan Feng, Xingwei Chen, Dai Dang, Kaibo Huang, Xueqin Tao, Hua Yin, Zhi DangAbstract:Abstract Polybrominated biphenyls (PBBs) are brominated flame retardants that are widely used in textiles and electronic products. Recently, many researches have been devoted to determining their concentrations in food and in the environment. Yet, their degradation behavior has been less investigated and is not well understood. Here, we have investigated the Debromination pathways of PBBs by (UV) light in the case of 2,4,5-tribrominated biphenyl (PBB-29). Our investigation indicates that para-bromine substituent on PBB-29 was preferentially removed. By means of density functional theory (DFT), we found that the energies of the Debromination products, the C Br bond length in the excited state (S1), the Mulliken charge of bromine in S1, and the lowest unoccupied molecular orbital (LUMO) in S1 correlated well with the Debromination pathways of PBBs. Further, LUMO-based prediction of PBB Debromination pathways in S1 suggests that the bromine substituent on all brominated positions (i.e. ortho-, meta- and para-) can be preferentially removed, as the Debromination sequence is not based on the brominated position but on the specific brominated arrangement pattern. In addition, reductive Debromination preferentially occurs on the benzene ring that has the highest number of bromine substituents. This study provided useful descriptors to predict the Debromination pathways of PBBs, and the theoretical result greatly improve our understanding of photolytic Debromination of PBBs.
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Debromination of polybrominated diphenyl ethers (PBDEs) by zero valent zinc: Mechanisms and predicting descriptors.
Journal of hazardous materials, 2018Co-Authors: Ting Tang, Rui Wang, Kaibo Huang, Xueqin Tao, Huan Chen, Yingcong Fang, Jiayi Zheng, Mengyao Zou, Hua YinAbstract:Abstract Polybrominated diphenyl ethers (PBDEs) are a class of brominated flame retardants that are ubiquitous in the environment. The physical and chemical properties of PBDEs make them difficult to degrade, with the conventional remediation methods being relatively inefficient. In this study, the reactivity of zero valent zinc (ZVZ) toward 2,2′,4,4′-tetrabromodiphenyl ether (BDE-47) was evaluated under aqueous solution. First-order rate constants (kobs) for BDE-47 disappearance increased with decreased pH, which is attributed to the dissolution of surface zinc oxides that promote the contact between the active site on zinc surface and BDE molecules. The kobs of ten investigated PBDEs in ZVZ system are positively correlated with the energy of lowest unoccupied orbitals (ELUMO) of PBDEs (R2 = 0.902). The Debromination pathways of BDE-47 in ZVZ system are: BDE-47 → BDE-28 → BDE-15 → BDE-3 → DE, which is the same to the Debromination pathways of BDE-47 in zero valent iron (ZVI) in previous study. In addition, the singly occupied molecular orbitals (SOMOs) of the BDE anions can well reflect the actual Debromination pathways of PBDEs by comparing the size of the C Br antibonding characterized lobes. Our results suggest that the Debromination of PBDEs by ZVZ is based on the electron transfer mechanism, and the SOMOs of BDE anions can be used to predict the Debromination pathways of untested PBDEs.
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relative roles of h atom transfer and electron transfer in the Debromination of polybrominated diphenyl ethers by palladized nanoscale zerovalent iron
Environmental Pollution, 2017Co-Authors: Rui Wang, Ting Tang, Kaibo Huang, Hua Yin, Haozhong Lin, Xiuling Xue, Xingjian Yang, Zhi DangAbstract:The relative significance of H-atom transfer versus electron transfer in the dehalogenation of halogenated organic compounds (HOCs) in bimetallic systems has long been debated. In this study, we have investigated this question through the case study of the Debromination of 2, 2', 4, 4'-tetrabromodiphenyl ether (BDE-47). The Debromination rates of isomer products of BDE-47 by palladized nano zero-valent iron (n-ZVI/Pd) in the same reactor were compared. The results confirmed a shift in the Debromination pathway of BDE-47 when treated with unpalladized nano zero-valent iron (n-ZVI) vs. treatment with n-ZVI/Pd. Study showed that BDEs could be rapidly debrominated in a palladium-H2 system, and the Debromination pathway in this system is the same as that in the n-ZVI/Pd system. These results suggest that the H-atom species adsorbed on the surface of palladium are responsible for the enhanced reaction rates and the shift of the Debromination pathway in the n-ZVI/Pd system. The Mulliken charges, calculated with density functional theory, on bromine atoms of PBDEs were directly correlated with the susceptibility to the e-transfer pathway in the n-ZVI system and inversely correlated with the susceptibility to the H-transfer pathway in n-ZVI/Pd system. These experimentally verified correlations in BDE-47 permit the prediction of the dominant Debromination pathway in other BDEs.
Ming Lei - One of the best experts on this subject based on the ideXlab platform.
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Complete Debromination of 2,2′,4,4′-tetrabromodiphenyl ether by visible-light photocatalysis on g-C3N4 supported Pd
Applied Catalysis B: Environmental, 2020Co-Authors: Ming Lei, Zhiying Wang, Lihua Zhu, Wenshan Nie, Heqing TangAbstract:Abstract Deep Debromination of polybrominated diphenyl ethers (PBDEs) by visible light photocatalysis is still a challenge in the field of halogenated pollutants control. Here, an efficient photocatalyst (Pd/g-C3N4) was prepared by a simple impregnation-chemical reduction method with bulk g-C3N4 and PdCl2 as precursors. Under preferred reaction conditions (visible light irradiation for 120 min), the use of the 0.5% Pd/g-C3N4 composites (0.4 g L−1) yielded an almost complete Debromination of BDE47 (10 μmol L−1) in methanol-water mixture, while the Debromination of BDE47 did not occur on pure g-C3N4. A “Pd-promoted active H atom species attack and C-Br bond cleavage” route was proposed according to the identified degradation intermediates. A catalytic mechanism was further clarified: Pd nanoparticles exerted affinity interaction with bromine atoms, and the storing of electrons on Pd would increase the binding interaction. In the Debromination process, methanol acts as both a hole scavenger and a hydrogen donor to provide active H atom species through the reaction of H+ and photogenerated electrons on Pd nanoparticles. The initiation of BDE47 Debromination on Pd nanoparticles required an induction period to enrich a critical amount of electrons for stretching the C-Br bond and its subsequent being attacked by active H atoms. The generated 2,2′-dibromodiphenyl ether (BDE4) would be further reduced to bromine-free products by hydro-Debromination process or coupling reaction.
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Peculiar and full Debromination of tetrabromodiphenyl ether on Pd/TiO2: A competing route through hydro-Debromination and coupling-Debromination
Applied Catalysis B: Environmental, 2020Co-Authors: Ming Lei, Zhiying Wang, Lihua Zhu, Yao Tang, Huimin Wang, Heqing TangAbstract:Abstract The use of palladium deposited TiO2 (Pd/TiO2) as catalysts yielded complete Debromination of 2,2′,4,4′-tetrabromodiphenyl ether (BDE47) in isopropanol solution containing NaOH at 40 °C within 60 min. The final organic products were diphenyl ether and dibenzofuran. It was disclosed that two competing reduction paths (hydro-Debromination and coupling-Debromination) occurred over Pd nanoparticles. The hydro-Debromination was dependent on the participation of active H atom species generated by catalytic transfer hydrogenation on metallic Pd. The coupling-Debromination proceeded via the oxidative addition of Pd(0) to B r 2 C 12 H 8 OB r 2 ′ , leading to an transition state of B r 2 Pd II C 12 H 8 OB r 2 ′ , the reductive dissociation of which resulted in the elimination of Br− ions, producing a new transition state Pd 0 C 12 H 8 OB r 2 ′ − . A further oxidative addition of Pd 0 C 12 H 8 OB r 2 ′ − generated B r 2 ′ Pd II C 12 H 8 O − , and its final reductive elimination provided dibenzofuran, leading to the regeneration of Pd(0). The integration of the catalytic coupling and hydrogenation reaction on Pd nanoparticles greatly accelerated the removal of the halogenated organic pollutants.
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Reductive Debromination of Polybrominated Diphenyl Ethers: Dependence on Br Number of the Br-Rich Phenyl Ring.
Environmental science & technology, 2019Co-Authors: Shun Guo, Ming Lei, Lihua Zhu, Tetsuro Majima, Heqing TangAbstract:Reductive Debromination has been widely studied for the degradation of polybrominated diphenyl ethers (PBDEs), although the reaction mechanisms are not so clear. In the present study, the photocatalytic degradation and Debromination of ten PBDEs were carried out with CuO/TiO2 nanocomposites as the photocatalyst under an anaerobic condition. The pseudo-first-order rate constants were obtained for the photocatalytic Debromination of PBDEs, and their relative rate constants ( kR) were evaluated against kR= 1 for BDE209. Unlike the generally accepted summary that kR is dependent on the total Br number ( N) of PBDEs, kR is found to depend on the Br number on a phenyl ring with more Br atoms than the other one. In other words, a phenyl ring substituted by more Br is more reactive for the reductive Debromination. The calculated LUMO energies ( ELUMO) of all PBDEs are well correlated to the more reactive phenyl ring with more Br, compared with the N of two phenyl rings. The result was explained by LUMO localization on the Br-rich phenyl ring, suggesting that the reductive Debromination occurs on the phenyl ring.
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Reductive Debromination of Polybrominated Diphenyl Ethers: Dependence on Br Number of the Br-Rich Phenyl Ring
2019Co-Authors: Shun Guo, Ming Lei, Lihua Zhu, Tetsuro Majima, Heqing TangAbstract:Reductive Debromination has been widely studied for the degradation of polybrominated diphenyl ethers (PBDEs), although the reaction mechanisms are not so clear. In the present study, the photocatalytic degradation and Debromination of ten PBDEs were carried out with CuO/TiO2 nanocomposites as the photocatalyst under an anaerobic condition. The pseudo-first-order rate constants were obtained for the photocatalytic Debromination of PBDEs, and their relative rate constants (kR) were evaluated against kR= 1 for BDE209. Unlike the generally accepted summary that kR is dependent on the total Br number (N) of PBDEs, kR is found to depend on the Br number on a phenyl ring with more Br atoms than the other one. In other words, a phenyl ring substituted by more Br is more reactive for the reductive Debromination. The calculated LUMO energies (ELUMO) of all PBDEs are well correlated to the more reactive phenyl ring with more Br, compared with the N of two phenyl rings. The result was explained by LUMO localization on the Br-rich phenyl ring, suggesting that the reductive Debromination occurs on the phenyl ring
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Ultrarapid and Deep Debromination of Tetrabromodiphenyl Ether over Noble-Metal-Free Cu/TiO2 Nanocomposites under Mild Conditions.
Environmental science & technology, 2018Co-Authors: Ming Lei, Shun Guo, Zhiying Wang, Lihua Zhu, Heqing TangAbstract:Fast and deep Debromination of polybrominated diphenyl ethers (PBDEs) under mild conditions is a challenge in the field of pollution control. A strategy was developed to achieve it by exploiting Cu/TiO2 composites as a noble-metal-free catalyst. Toward the Debromination of 2,2′,4,4′-tetrabromodiphenyl ether (BDE47) as a typical PBDE, the use of Cu/TiO2 as a catalyst and hydrazine hydrate (N2H4·H2O) as a reducing agent yielded a degradation removal of 100% and a Debromination efficiency of 87.7% in 3 s. A complete Debromination of BDE47 at 1500 mg L–1 was possible by successively adding N2H4·H2O. A Debromination pathway involving active H atom species was proposed for the catalytic transfer hydrogenation (CTH) of PBDEs according to the identified degradation intermediates. A mechanism was further clarified by density functional theory calculations: electrons are delivered from N2H4·H2O to the metallic Cu atom via a coordination of N in N2H4·H2O with Cu atoms. The electron-trapped Cu atom interacts with ads...
Rui Wang - One of the best experts on this subject based on the ideXlab platform.
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rapid Debromination of polybrominated diphenyl ethers pbdes by zero valent metal and bimetals mechanisms and pathways assisted by density function theory calculation
Environmental Pollution, 2018Co-Authors: Rui Wang, Ting Tang, Kaibo Huang, Hua Yin, Zhang Lin, Zhi DangAbstract:Polybrominated diphenyl ethers (PBDEs) undergo Debromination when they were exposed in zerovalent metal or bimetallic systems. Yet their Debromination pathways and mechanisms in these systems were not well understood. Here we reported the Debromination pathways of three BDE congeners (BDE-21, 25 and 29) by nano-zerovalent iron (n-ZVI). All these BDE congeners have three bromine substituents that were located in ortho-, meta- and para-positions. Results demonstrated that BDE-21, 25 and 29 preferentially debrominate meta-, ortho- and para-bromines, respectively, suggesting that bromine substituent at each position (i.e. ortho-, meta- or para-) of PBDEs can be preferentially removed. Singly occupied molecular orbitals of BDE anions are well correlated with their actual Debromination pathways, which successfully explain why these BDE congeners exhibit certain Debromination pathways in n-ZVI system. In addition, microscale zerovalent zinc (m-ZVZ), iron-based bimetals (Fe/Ag and Fe/Pd) were also used to debrominate PBDEs, with BDE-21 as target pollutant. We found that the Debromination pathways of BDE-21 in m-ZVZ and Fe/Ag systems are the same to those in n-ZVI system, but were partially different from those in Fe/Pd systems. The Debromination of BDE-21 in Pd-H2 system as well as the solvent kinetic isotope effect in single metal and bimetallic systems suggests that H atom transfer is the dominant mechanism in Fe/Pd system, while e-transfer is still the dominant mechanism in Fe/Ag system.
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Experimental and theoretical investigations on Debromination pathways of polybrominated biphenyls (PBBs) under ultraviolet light.
Chemosphere, 2018Co-Authors: Rui Wang, Ting Tang, Siyuan Feng, Xingwei Chen, Dai Dang, Kaibo Huang, Xueqin Tao, Hua Yin, Zhi DangAbstract:Abstract Polybrominated biphenyls (PBBs) are brominated flame retardants that are widely used in textiles and electronic products. Recently, many researches have been devoted to determining their concentrations in food and in the environment. Yet, their degradation behavior has been less investigated and is not well understood. Here, we have investigated the Debromination pathways of PBBs by (UV) light in the case of 2,4,5-tribrominated biphenyl (PBB-29). Our investigation indicates that para-bromine substituent on PBB-29 was preferentially removed. By means of density functional theory (DFT), we found that the energies of the Debromination products, the C Br bond length in the excited state (S1), the Mulliken charge of bromine in S1, and the lowest unoccupied molecular orbital (LUMO) in S1 correlated well with the Debromination pathways of PBBs. Further, LUMO-based prediction of PBB Debromination pathways in S1 suggests that the bromine substituent on all brominated positions (i.e. ortho-, meta- and para-) can be preferentially removed, as the Debromination sequence is not based on the brominated position but on the specific brominated arrangement pattern. In addition, reductive Debromination preferentially occurs on the benzene ring that has the highest number of bromine substituents. This study provided useful descriptors to predict the Debromination pathways of PBBs, and the theoretical result greatly improve our understanding of photolytic Debromination of PBBs.
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Debromination of polybrominated diphenyl ethers (PBDEs) by zero valent zinc: Mechanisms and predicting descriptors.
Journal of hazardous materials, 2018Co-Authors: Ting Tang, Rui Wang, Kaibo Huang, Xueqin Tao, Huan Chen, Yingcong Fang, Jiayi Zheng, Mengyao Zou, Hua YinAbstract:Abstract Polybrominated diphenyl ethers (PBDEs) are a class of brominated flame retardants that are ubiquitous in the environment. The physical and chemical properties of PBDEs make them difficult to degrade, with the conventional remediation methods being relatively inefficient. In this study, the reactivity of zero valent zinc (ZVZ) toward 2,2′,4,4′-tetrabromodiphenyl ether (BDE-47) was evaluated under aqueous solution. First-order rate constants (kobs) for BDE-47 disappearance increased with decreased pH, which is attributed to the dissolution of surface zinc oxides that promote the contact between the active site on zinc surface and BDE molecules. The kobs of ten investigated PBDEs in ZVZ system are positively correlated with the energy of lowest unoccupied orbitals (ELUMO) of PBDEs (R2 = 0.902). The Debromination pathways of BDE-47 in ZVZ system are: BDE-47 → BDE-28 → BDE-15 → BDE-3 → DE, which is the same to the Debromination pathways of BDE-47 in zero valent iron (ZVI) in previous study. In addition, the singly occupied molecular orbitals (SOMOs) of the BDE anions can well reflect the actual Debromination pathways of PBDEs by comparing the size of the C Br antibonding characterized lobes. Our results suggest that the Debromination of PBDEs by ZVZ is based on the electron transfer mechanism, and the SOMOs of BDE anions can be used to predict the Debromination pathways of untested PBDEs.
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relative roles of h atom transfer and electron transfer in the Debromination of polybrominated diphenyl ethers by palladized nanoscale zerovalent iron
Environmental Pollution, 2017Co-Authors: Rui Wang, Ting Tang, Kaibo Huang, Hua Yin, Haozhong Lin, Xiuling Xue, Xingjian Yang, Zhi DangAbstract:The relative significance of H-atom transfer versus electron transfer in the dehalogenation of halogenated organic compounds (HOCs) in bimetallic systems has long been debated. In this study, we have investigated this question through the case study of the Debromination of 2, 2', 4, 4'-tetrabromodiphenyl ether (BDE-47). The Debromination rates of isomer products of BDE-47 by palladized nano zero-valent iron (n-ZVI/Pd) in the same reactor were compared. The results confirmed a shift in the Debromination pathway of BDE-47 when treated with unpalladized nano zero-valent iron (n-ZVI) vs. treatment with n-ZVI/Pd. Study showed that BDEs could be rapidly debrominated in a palladium-H2 system, and the Debromination pathway in this system is the same as that in the n-ZVI/Pd system. These results suggest that the H-atom species adsorbed on the surface of palladium are responsible for the enhanced reaction rates and the shift of the Debromination pathway in the n-ZVI/Pd system. The Mulliken charges, calculated with density functional theory, on bromine atoms of PBDEs were directly correlated with the susceptibility to the e-transfer pathway in the n-ZVI system and inversely correlated with the susceptibility to the H-transfer pathway in n-ZVI/Pd system. These experimentally verified correlations in BDE-47 permit the prediction of the dominant Debromination pathway in other BDEs.
