1
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St Onge P, Khan SI, Cook A, Newman SG. Reductive Cleavage of C(sp 2)-CF 3 Bonds in Trifluoromethylpyridines. Org Lett 2023; 25:1030-1034. [PMID: 36749351 DOI: 10.1021/acs.orglett.3c00258] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Abstract
A reductive detrifluoromethylation protocol has been developed making use of an earth-abundant alkoxide base and silicon hydride species. A variety of pyridine and quinoline substrates bearing alkyl, aryl, and amino functional groups are reduced in moderate to high yields. The reaction is chemoselective for C(sp2)-CF3 groups located at the 2-position on the pyridine ring, leaving trifluoromethyl groups located elsewhere on the molecule intact. Preliminary mechanistic studies demonstrate that the combination of silane and base generates a strongly reducing system that may transfer an electron to electron-deficient π systems.
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Affiliation(s)
- Piers St Onge
- Centre for Catalysis Research and Innovation, Department of Chemistry and Biomolecular Sciences, University of Ottawa, 10 Marie Curie, Ottawa, Ontario K1N 6N5, Canada
| | - Shajia I Khan
- Centre for Catalysis Research and Innovation, Department of Chemistry and Biomolecular Sciences, University of Ottawa, 10 Marie Curie, Ottawa, Ontario K1N 6N5, Canada
| | - Adam Cook
- Centre for Catalysis Research and Innovation, Department of Chemistry and Biomolecular Sciences, University of Ottawa, 10 Marie Curie, Ottawa, Ontario K1N 6N5, Canada
| | - Stephen G Newman
- Centre for Catalysis Research and Innovation, Department of Chemistry and Biomolecular Sciences, University of Ottawa, 10 Marie Curie, Ottawa, Ontario K1N 6N5, Canada
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2
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Xu Y, Liang C, Zhang T, Tao X, Wang R, Huang K, Pan Z, Dang Z, Yin H, Lu G. Debromination of polybrominated diphenyl ethers (PBDEs) by palladized zerovalent zinc particles: Influence factors, pathways and mechanism. CHEMOSPHERE 2020; 253:126726. [PMID: 32302906 DOI: 10.1016/j.chemosphere.2020.126726] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/25/2019] [Revised: 02/26/2020] [Accepted: 04/05/2020] [Indexed: 06/11/2023]
Abstract
We synthesized a novel material, namely palladized zero-valent zinc (Pd/ZVZ), and investigated its efficiency for the degradation of polybrominated diphenyl ethers (PBDEs). The plated Pd significantly enhances the degradation rate of PBDEs by ZVZ at the optimum loading of 1% by weight. In the Pd/ZVZ system, very few lower BDEs were accumulated during the degradation of 2,2',4,4'- tetrabromodiphenyl ether (BDE-47) and the final product is diphenyl ether, whereas the ZVZ system only debrominates BDE-47 to di-BDE and further debromination becomes very difficult. The degradation rates of BDEs by ZVZ greatly decreased with decreased bromination level, while in Pd/ZVZ system, the degradation rates of PBDEs did not show a significant difference. These indicate different mechanisms. This was confirmed by investigating the debromination pathways of the PBDEs in both systems. We determined that a H-transfer was the dominant mechanism in the Pd/ZVZ system. In addition, the reactivity of Pd/ZVZ to BDE-47 is pH-independent, which has a great advantage for various applications over ZVZ alone. Our study provides a new approach for the remediation of the PBDEs pollution.
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Affiliation(s)
- Yongye Xu
- School of Environment and Energy, South China University of Technology, Guangzhou, 510006, China
| | - Chenghao Liang
- School of Environment and Energy, South China University of Technology, Guangzhou, 510006, China
| | - Taiping Zhang
- School of Environment and Energy, South China University of Technology, Guangzhou, 510006, China; The Key Lab of Pollution Control and Ecosystem Restoration in Industry Clusters, Ministry of Education, Guangzhou, 510006, China.
| | - Xueqin Tao
- School of Environmental Science and Engineering, Zhongkai University of Agriculture and Engineering, Guangzhou, 510225, China
| | - Rui Wang
- School of Environment and Energy, South China University of Technology, Guangzhou, 510006, China
| | - Kaibo Huang
- School of Environment and Energy, South China University of Technology, Guangzhou, 510006, China
| | - Zhaoxi Pan
- School of Environmental Science and Engineering, Zhongkai University of Agriculture and Engineering, Guangzhou, 510225, China
| | - Zhi Dang
- School of Environment and Energy, South China University of Technology, Guangzhou, 510006, China; The Key Lab of Pollution Control and Ecosystem Restoration in Industry Clusters, Ministry of Education, Guangzhou, 510006, China
| | - Hua Yin
- School of Environment and Energy, South China University of Technology, Guangzhou, 510006, China; The Key Lab of Pollution Control and Ecosystem Restoration in Industry Clusters, Ministry of Education, Guangzhou, 510006, China
| | - Guining Lu
- School of Environment and Energy, South China University of Technology, Guangzhou, 510006, China; The Key Lab of Pollution Control and Ecosystem Restoration in Industry Clusters, Ministry of Education, Guangzhou, 510006, China.
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3
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Hadnagy E, Mai A, Smolinski B, Braida W, Koutsospyros A. Characterization of Mg-based bimetal treatment of insensitive munition 2,4-dinitroanisole. ENVIRONMENTAL SCIENCE AND POLLUTION RESEARCH INTERNATIONAL 2018; 25:24403-24416. [PMID: 29909531 DOI: 10.1007/s11356-018-2493-1] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/22/2018] [Accepted: 06/04/2018] [Indexed: 06/08/2023]
Abstract
The manufacturing of insensitive munition 2,4-dinitroanisole (DNAN) generates waste streams that require treatment. DNAN has been treated previously with zero-valent iron (ZVI) and Fe-based bimetals. Use of Mg-based bimetals offers certain advantages including potential higher reactivity and relative insensitivity to pH conditions. This work reports preliminary findings of DNAN degradation by three Mg-based bimetals: Mg/Cu, Mg/Ni, and Mg/Zn. Treatment of DNAN by all three bimetals is highly effective in aqueous solutions (> 89% removal) and wastewater (> 91% removal) in comparison with treatment solely with zero-valent magnesium (ZVMg; 35% removal). Investigation of reaction byproducts supports a partial degradation pathway involving reduction of the ortho or para nitro to amino group, leading to 2-amino-4-nitroanisole (2-ANAN) and 4-amino-2-nitroanisole (4-ANAN). Further reduction of the second nitro group leads to 2,4-diaminoanisole (DAAN). These byproducts are detected in small quantities in the aqueous phase. Carbon mass balance analysis suggests near-complete closure (91%) with 12.4 and 78.4% of the total organic carbon (TOC) distributed in the aqueous and mineral bimetal phases, respectively. Post-treatment surface mineral phase analysis indicates Mg(OH)2 as the main oxidized species; oxide formation does not appear to impair treatment.
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Affiliation(s)
- Emese Hadnagy
- Department of Civil and Environmental Engineering, University of New Haven, West Haven, CT, USA.
| | - Andrew Mai
- Department of Civil, Environmental, and Ocean Engineering, Stevens Institute of Technology, Hoboken, NJ, USA
| | | | - Washington Braida
- Department of Civil, Environmental, and Ocean Engineering, Stevens Institute of Technology, Hoboken, NJ, USA
| | - Agamemnon Koutsospyros
- Department of Civil and Environmental Engineering, University of New Haven, West Haven, CT, USA
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4
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Kostenko EA, Eliseenkov EV, Petrov AA. Regularities of Pd/C-catalyzed reduction of trichlorobiphenyls with 2-propanol in basic medium. RUSS J GEN CHEM+ 2017. [DOI: 10.1134/s1070363217080023] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
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5
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Wan H, Briot NJ, Saad A, Ormsbee L, Bhattacharyya D. Pore Functionalized PVDF Membranes with In-Situ Synthesized Metal Nanoparticles: Material Characterization, and Toxic Organic Degradation. J Memb Sci 2017; 530:147-157. [PMID: 29398774 PMCID: PMC5793928 DOI: 10.1016/j.memsci.2017.02.021] [Citation(s) in RCA: 28] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/20/2022]
Abstract
Functionalized PVDF membrane platforms were developed for environmentally benign in-situ nanostructured Fe/Pd synthesis and remediation of chlorinated organic compounds. To prevent leaching and aggregation, nanoparticle catalysts were integrated into membrane domains functionalized with poly (acrylic acid). Nanoparticles of 16-19 nm were observed inside the membrane pores by using focused ion beam (FIB). This technique prevents mechanical deformation of the membrane, compared to the normal SEM preparation methods, thus providing a clean, smooth surface for nanoparticles characterization. This allowed quantification of nanoparticle properties (size and distribution) versus depth underneath the membrane surface (0-20 µm). The results showed that nanoparticles were uniformly sized and evenly distributed inside the membrane pores. However, the size of nanoparticles inside the membrane pores was 13.9% smaller than those nanoparticles located on the membrane surface. Investigating nanoparticles inside membrane pores increases the accuracy of kinetic analysis and modeling aspects. Furthermore, the Fe/Pd immobilized membranes showed excellent performance in the degradation of chlorinated organics: Over 96% degradation of 3,3',4,4',5-pentachlorobiphenyl (PCB 126) was achieved in less than 15 s residence time in convective flow mode. The regeneration and reuse of this catalytic membrane system were also studied. Particles were examined in XRD upon formation, after deliberate oxidation, and after regeneration. The regenerated sample showed the same crystalline pattern as the original sample. Repeated degradation experiments demonstrated successful PCB 126 dechlorination with nanoparticles regenerated for four cycles with only a small loss in reactivity. It demonstrated that Fe/Pd immobilized membranes have the potential for large-scale remediation applications.
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Affiliation(s)
- Hongyi Wan
- Department of Chemical and Materials Engineering, University of Kentucky, Lexington, Kentucky 40506-0046
| | - Nicolas J. Briot
- Department of Chemical and Materials Engineering, University of Kentucky, Lexington, Kentucky 40506-0046
| | - Anthony Saad
- Department of Chemical and Materials Engineering, University of Kentucky, Lexington, Kentucky 40506-0046
| | - Lindell Ormsbee
- Department of Civil Engineering, University of Kentucky, Lexington, Kentucky 40506-0046
| | - Dibakar Bhattacharyya
- Department of Chemical and Materials Engineering, University of Kentucky, Lexington, Kentucky 40506-0046
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6
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Wang R, Lu G, Lin H, Huang K, Tang T, Xue X, Yang X, Yin H, Dang Z. Relative roles of H-atom transfer and electron transfer in the debromination of polybrominated diphenyl ethers by palladized nanoscale zerovalent iron. ENVIRONMENTAL POLLUTION (BARKING, ESSEX : 1987) 2017; 222:331-337. [PMID: 28034557 DOI: 10.1016/j.envpol.2016.12.030] [Citation(s) in RCA: 31] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/09/2016] [Revised: 12/05/2016] [Accepted: 12/07/2016] [Indexed: 06/06/2023]
Abstract
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.
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Affiliation(s)
- Rui Wang
- School of Environment and Energy, South China University of Technology, Guangzhou 510006, China
| | - Guining Lu
- School of Environment and Energy, South China University of Technology, Guangzhou 510006, China; The Key Lab of Pollution Control and Ecosystem Restoration in Industry Clusters, Ministry of Education, Guangzhou 510006, China; Guangdong Provincial Engineering and Technology Research Center for Environmental Risk Prevention and Emergency Disposal, Guangzhou 510006, China.
| | - Haozhong Lin
- School of Environment and Energy, South China University of Technology, Guangzhou 510006, China
| | - Kaibo Huang
- School of Environment and Energy, South China University of Technology, Guangzhou 510006, China
| | - Ting Tang
- School of Environment and Energy, South China University of Technology, Guangzhou 510006, China
| | - Xiuling Xue
- School of Chemical Engineering, Huaqiao University, Xiamen 361021, China
| | - Xingjian Yang
- School of Environment and Energy, South China University of Technology, Guangzhou 510006, China
| | - Hua Yin
- School of Environment and Energy, South China University of Technology, Guangzhou 510006, China; The Key Lab of Pollution Control and Ecosystem Restoration in Industry Clusters, Ministry of Education, Guangzhou 510006, China
| | - Zhi Dang
- School of Environment and Energy, South China University of Technology, Guangzhou 510006, China; The Key Lab of Pollution Control and Ecosystem Restoration in Industry Clusters, Ministry of Education, Guangzhou 510006, China; Guangdong Provincial Engineering and Technology Research Center for Environmental Risk Prevention and Emergency Disposal, Guangzhou 510006, China.
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7
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Liu C, Zhang AY, Pei DN, Yu HQ. Efficient Electrochemical Reduction of Nitrobenzene by Defect-Engineered TiO2-x Single Crystals. ENVIRONMENTAL SCIENCE & TECHNOLOGY 2016; 50:5234-5242. [PMID: 27128346 DOI: 10.1021/acs.est.6b00730] [Citation(s) in RCA: 57] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
TiO2 is a typical semiconductor and has been extensively used as an effective photocatalyst for environmental pollution control. But it could not be used as an electrochemical reductive catalyst because of its low electric conductivity and electrocatalytic activity. In this work, however, we demonstrate that TiO2 can act as an excellent cathodic electrocatalyst when its crystal shape, exposed facet and oxygen-stoichiometry are finely tailored by the local geometric and electronic structures. The defect-engineered TiO2-x single crystals dominantly exposed by high-energy {001} facets exhibits a high cathodic activity and great stability for electrochemical reduction of nitrobenzene, a typical refractory pollutant with high toxicity in environment. The single crystalline structure, the high-energy {001} facet and the defective oxygen vacancy of the defect-engineered TiO2-x single crystals are found to be mainly responsible for their cathodic superiority. With the findings in this work, a more practical non-Pd cathodic electrocatalyst could be prepared and applied for electrocatalytic reduction of refractory pollutants in water and wastewater, and extend the promising applications of TiO2 in the fields of environmental science.
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Affiliation(s)
- Chang Liu
- CAS Key Laboratory of Urban Pollutants Conversion, Department of Chemistry, University of Science and Technology of China , Hefei, 230026, China
| | - Ai-Yong Zhang
- CAS Key Laboratory of Urban Pollutants Conversion, Department of Chemistry, University of Science and Technology of China , Hefei, 230026, China
- Department of Municipal Engineering, Hefei University of Technology , Hefei, 230009, China
| | - Dan-Ni Pei
- CAS Key Laboratory of Urban Pollutants Conversion, Department of Chemistry, University of Science and Technology of China , Hefei, 230026, China
| | - Han-Qing Yu
- CAS Key Laboratory of Urban Pollutants Conversion, Department of Chemistry, University of Science and Technology of China , Hefei, 230026, China
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8
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Abstract
The chronological development of metal assisted defunctionalization reactions is discussed from the stoichiometric to the catalytic stage with their application in synthetic organic chemistry.
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Affiliation(s)
- Atanu Modak
- Department of Chemistry
- Indian Institute of Technology
- Mumbai
- India
| | - Debabrata Maiti
- Department of Chemistry
- Indian Institute of Technology
- Mumbai
- India
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9
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Zhou Y, Tang L, Yang G, Zeng G, Deng Y, Huang B, Cai Y, Tang J, Wang J, Wu Y. Phosphorus-doped ordered mesoporous carbons embedded with Pd/Fe bimetal nanoparticles for the dechlorination of 2,4-dichlorophenol. Catal Sci Technol 2016. [DOI: 10.1039/c5cy01514f] [Citation(s) in RCA: 63] [Impact Index Per Article: 7.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Pd–Fe bimetal nanoparticles embedded within phosphorus-doped ordered mesoporous carbons as highly active and stable catalysts for the degradation of 2,4-dichlorophenol.
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10
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Le TT, Nguyen KH, Jeon JR, Francis AJ, Chang YS. Nano/bio treatment of polychlorinated biphenyls with evaluation of comparative toxicity. JOURNAL OF HAZARDOUS MATERIALS 2015; 287:335-41. [PMID: 25679799 DOI: 10.1016/j.jhazmat.2015.02.001] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/18/2014] [Revised: 01/31/2015] [Accepted: 02/01/2015] [Indexed: 05/24/2023]
Abstract
The persistence of polychlorinated biphenyl (PCB) Aroclor 1248 in soils and sediments is a major concern because of its toxicity and presence at high concentrations. In this study, we developed an integrated remediation system for PCBs using chemical catalysis and biodegradation. The dechlorination of Aroclor 1248 was achieved by treatment with bimetallic nanoparticles Pd/nFe under anoxic conditions. Among the 32 PCB congeners of Aroclor 1248 examined, our process dechlorinated 99%, 92%, 84%, and 28% of tri-, tetra-, penta-, and hexachlorinated biphenyls, respectively. The resulting biphenyl was biodegraded rapidly by Burkholderia xenovorans LB400. Benzoic acid was detected as an intermediate during the biodegradation process. The toxicity of the residual PCBs after nano-bio treatment was evaluated in terms of toxic equivalent values which decreased from 33.8×10(-5)μgg(-1) to 9.5×10(-5)μgg(-1). The residual PCBs also had low cytotoxicity toward Escherichia coli as demonstrated by lower reactive oxygen species levels, lower glutathione peroxidase activity, and a reduced number of dead bacteria.
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Affiliation(s)
- Thao Thanh Le
- School of Environmental Science and Engineering, POSTECH, Pohang 790-784, Republic of Korea
| | - Khanh-Hoang Nguyen
- School of Environmental Science and Engineering, POSTECH, Pohang 790-784, Republic of Korea
| | - Jong-Rok Jeon
- Corporate R&D, LG Chem Research Park, Daejeon 305-380, Republic of Korea
| | - Arokiasamy J Francis
- Division of Advanced Nuclear Engineering, POSTECH, Pohang 790-784, Republic of Korea; Environmental Sciences Department, Brookhaven National Laboratory, Upton, NY, USA
| | - Yoon-Seok Chang
- School of Environmental Science and Engineering, POSTECH, Pohang 790-784, Republic of Korea.
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11
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Virkutyte J, Al-Abed SR, Choi H, Bennett-Stamper C. Distinct structural behavior and transport of TiO 2 nano- and nanostructured particles in sand. Colloids Surf A Physicochem Eng Asp 2014. [DOI: 10.1016/j.colsurfa.2013.11.004] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
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12
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Sun G, Zhang L, Zhang G, Fan Y, Wang Y, Lu G. Nickel Complexes Catalyzed Hydrodechlorination of Aryl Chlorides in Ionic Liquid. J CHIN CHEM SOC-TAIP 2013. [DOI: 10.1002/jccs.201300134] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
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13
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Fang GD, Zhou DM, Dionysiou DD. Superoxide mediated production of hydroxyl radicals by magnetite nanoparticles: demonstration in the degradation of 2-chlorobiphenyl. JOURNAL OF HAZARDOUS MATERIALS 2013; 250-251:68-75. [PMID: 23434481 DOI: 10.1016/j.jhazmat.2013.01.054] [Citation(s) in RCA: 68] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/06/2012] [Revised: 12/03/2012] [Accepted: 01/23/2013] [Indexed: 05/27/2023]
Abstract
Increasing attention has been paid to magnetite nanoparticles (MNPs) due to their highly reductive reactivity toward environmental contaminants. However, there is little information related to the generation of reactive oxygen species (ROS) by MNPs, which in fact plays a vital role for the transformation of contaminants. In this paper, the degradation of 2-chlorobiphenyl (2-CB) by MNPs was investigated. The role of ROS generated by MNPs in this process was elucidated. The results demonstrated that hydroxyl radicals (OH) generated by MNPs at low pH could efficiently degrade 2-CB. The mechanism of the formation of OH by MNPs was divided into two steps: (i) the superoxide radical anion (O2(-)) mediated production of hydrogen peroxide (H2O2), and (ii) the reaction of formed H2O2 with Fe(II) dissolved from MNPs to produce OH through Fenton reaction. Comparison of the degradation products of 2-CB by MNPs with MNPs/ethanol and Fenton reagents further supported the involvement of OH in the degradation of 2-CB. The degradation efficiency of 2-CB by MNPs under acidic conditions was higher than that in alkaline solution. These findings provide a new insight into the understanding of reactivity of MNPs for the transformation of 2-CB and possibly other relevant environmental contaminants.
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Affiliation(s)
- Guo-Dong Fang
- Key Laboratory of Soil Environment and Pollution Remediation, Institute of Soil Science, Chinese Academy of Sciences, Nanjing 210008, PR China
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14
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Zahran EM, Bhattacharyya D, Bachas LG. Reactivity of Pd/Fe bimetallic nanotubes in dechlorination of coplanar polychlorinated biphenyls. CHEMOSPHERE 2013; 91:165-71. [PMID: 23332879 PMCID: PMC4526161 DOI: 10.1016/j.chemosphere.2012.12.037] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/10/2012] [Accepted: 12/16/2012] [Indexed: 05/07/2023]
Abstract
A new class of bimetallic materials based on palladium-decorated iron nanotubes is described that demonstrates high reactivity in dechlorination reactions. This high dechlorination efficiency was attributed to the high surface area to volume ratio of the hollow nanotubes structure. Herein, we evaluated the effect of different conditions, such as the nanotube size, and the palladium loading on the efficiency of the dechlorination of PCB 77, a model coplanar polychlorinated biphenyl (PCB), by the Pd/Fe bimetallic nanotubes system. The efficiency of the dechlorination was lowered by decreasing the tube diameter from 200 to 100 nm. In addition, the interior surface as well as the exterior surface of the as-synthesized Pd/Fe bimetallic nanotubes was found to contribute to the high efficiency of the dechlorination of PCB 77. The dechlorination of PCB 77 by Pd/Fe bimetallic nanotubes demonstrated small activation energy indicating diffusion controlled reaction. The as-prepared Pd/Fe bimetallic nanotubes showed extended lifetime activity when used in multiple dechlorination cycles.
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Affiliation(s)
- Elsayed M. Zahran
- Department of Chemistry, University of Miami, Coral Gables, FL 33146
| | - Dibakar Bhattacharyya
- Department of Chemical and Materials Engineering, University of Kentucky, Lexington, KY 40506
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15
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Fang GD, Dionysiou DD, Zhou DM, Wang Y, Zhu XD, Fan JX, Cang L, Wang YJ. Transformation of polychlorinated biphenyls by persulfate at ambient temperature. CHEMOSPHERE 2013; 90:1573-1580. [PMID: 22921645 DOI: 10.1016/j.chemosphere.2012.07.047] [Citation(s) in RCA: 84] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/29/2012] [Revised: 07/15/2012] [Accepted: 07/21/2012] [Indexed: 06/01/2023]
Abstract
Increasing attention has been paid to persulfate due to its high efficiency in degrading organic pollutants. This paper investigated the transformation of a selected polychlorinated biphenyl (PCB) by sodium persulfate without activators at near ambient temperature (10-40°C). The results showed that 2,4,4'-CB was completely decomposed by persulfate at 30°C in 8 h. The products were identified by gas chromatography-mass spectrometry (GC-MS), and transformation pathways could be divided into two steps as dechlorination and hydroxylation. Electron paramagnetic resonance (EPR) technique was used to identify the generated radical species at different pH values at ambient temperature. The results showed that sulfate radicals (SO(4)(•-)) were predominant under acidic condition and hydroxyl radicals ((•)OH) were predominant under basic condition. This behavior was also confirmed by the quenching studies and kinetic model. Decreasing the solution pH resulted in increasing the degradation efficiency of 2,4,4'-CB. Moreover, the degradation of other PCBs such as 2-CB, 4-CB, 2,4-CB, 2,4'-CB, and 2,4,6-CB with persulfate was examined. The findings of this study can provide guidance in the remediation of PCBs contaminated soil and water with persulfate.
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Affiliation(s)
- Guo-Dong Fang
- Key Laboratory of Soil Environment and Pollution Remediation, Institute of Soil Science, Chinese Academy of Sciences, Nanjing 210008, PR China
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16
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Zhuang Y, Jin L, Luthy RG. Kinetics and pathways for the debromination of polybrominated diphenyl ethers by bimetallic and nanoscale zerovalent iron: effects of particle properties and catalyst. CHEMOSPHERE 2012; 89:426-32. [PMID: 22732301 PMCID: PMC3408778 DOI: 10.1016/j.chemosphere.2012.05.078] [Citation(s) in RCA: 53] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/02/2012] [Revised: 04/08/2012] [Accepted: 05/16/2012] [Indexed: 05/13/2023]
Abstract
Polybrominated diphenyl ethers (PBDEs) are recognized as a new class of widely-distributed and persistent contaminants for which effective treatment and remediation technologies are needed. In this study, two kinds of commercially available nanoscale Fe(0) slurries (Nanofer N25 and N25S), a freeze-dried laboratory-synthesized Fe(0) nanoparticle (nZVI), and their palladized forms were used to investigate the effect of particle properties and catalyst on PBDE debromination kinetics and pathways. Nanofers and their palladized forms were found to debrominate PBDEs effectively. The laboratory-synthesized Fe(0) nanoparticles also debrominated PBDEs, but were slower due to deactivation by the freeze-drying and stabilization processes in the laboratory synthesis. An organic modifier, polyacrylic acid (PAA), bound on N25S slowed PBDE debromination by a factor of three to four compared to N25. The activity of palladized nZVI (nZVI/Pd) was optimized at 0.3 Pd/Fe wt% in our system. N25 could debrominate selected environmentally-abundant PBDEs, including BDE 209, 183, 153, 99, and 47, to end products di-BDEs, mono-BDEs and diphenyl ether (DE) in one week, while nZVI/Pd (0.3 Pd/Fe wt%) mainly resulted in DE as a final product. Step-wise major PBDE debromination pathways by unamended and palladized Fe(0) are described and compared. Surface precursor complex formation is an important limiting factor for palladized Fe(0) reduction as demonstrated by PBDE pathways where steric hindrance and rapid sequential debromination of adjacent bromines play an important role.
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Affiliation(s)
| | | | - Richard G. Luthy
- Corresponding author phone: (650) 721-2615; fax: (650) 725-9720;
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Ishihara S, Ido A, Monguchi Y, Nagase H, Sajiki H. Pd/C-catalyzed dechlorination of polychlorinated biphenyls under hydrogen gas-free conditions. JOURNAL OF HAZARDOUS MATERIALS 2012; 229-230:15-9. [PMID: 22738771 DOI: 10.1016/j.jhazmat.2012.05.005] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/02/2012] [Revised: 04/18/2012] [Accepted: 05/02/2012] [Indexed: 05/10/2023]
Abstract
The simultaneous use of catalytic amount of palladium on carbon (Pd/C) and Mg metal (1.5-2.0 equiv vs. Cl numbers of the substrates) in MeOH achieved the complete dechlorination of a variety of aryl chlorides at room temperature under a nitrogen atmosphere in the absence of hydrogen gas. The present method could be successfully used for the detoxification of PCBs based on the dechlorination reaction. Both virgin PCBs, such as Aroclors 1242, 1248 and 1254, and used PCBs as a high-tension capacitor oil, were smoothly dechlorinated into harmless biphenyl without any byproducts within 2h at rt. The distinctive features of this method are convenience and safety due to no needs for the pretreatment of catalyst and Mg and complete degradation of PCBs under mild conditions without hydrogen gas.
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Affiliation(s)
- Shinji Ishihara
- Laboratory of Organic Chemistry, Gifu Pharmaceutical University, 1-25-1 Daigaku-nishi, Gifu 501-1196, Japan
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18
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Wu BZ, Chen HY, Wang SJ, Wai CM, Liao W, Chiu K. Reductive dechlorination for remediation of polychlorinated biphenyls. CHEMOSPHERE 2012; 88:757-768. [PMID: 22572168 DOI: 10.1016/j.chemosphere.2012.03.056] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/17/2011] [Revised: 03/06/2012] [Accepted: 03/18/2012] [Indexed: 05/31/2023]
Abstract
Technologies such as thermal, oxidative, reductive, and microbial methods for the remediation of polychlorinated biphenyls (PCBs) have previously been reviewed. Based on energy consumption, formation of PCDD/F, and remediation efficiency, reductive methods have emerged as being advantageous for remediation of PCBs. However, many new developments in this field have not been systematically reviewed. Therefore, reductive technologies published in the last decade related to remediation of PCBs will be reviewed here. Three categories, including catalytic hydrodechlorination with H(2), Fe-based reductive dechlorination, and other reductive dechlorination methods (e.g., hydrogen-transfer dechlorination, base-catalyzed dechlorination, and sodium dispersion) are specifically reviewed. In addition, the advantages of each remediation technology are discussed. In this review, 108 articles are referenced.
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Affiliation(s)
- Ben-Zen Wu
- Department of Chemistry, National Dong Hwa University, Hualien 97401, Taiwan, ROC
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19
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A theoretical study on reductive debromination of polybrominated diphenyl ethers. Int J Mol Sci 2012; 13:9332-9342. [PMID: 22942768 PMCID: PMC3430299 DOI: 10.3390/ijms13079332] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/24/2012] [Revised: 07/08/2012] [Accepted: 07/18/2012] [Indexed: 12/03/2022] Open
Abstract
Recent progress has been made in the reductive debromination of polybrominated diphenyl ethers (PBDEs) by nanoscale zero-valent iron (nZVI). To better understand the mechanism of this reaction, seven selected BDE congeners and their anions were investigated at the density functional theory (DFT) level using four different methods, including B3LYP/6-31G(d), B3LYP/6-31+G(d), B3LYP/6-31G(d,p) and B3LYP/6-311G(d,p). The cleaved C–Br bonds observed in the equilibrium structures of anionic PBDEs were adopted as the probe of the susceptible debromination position of PBDEs in the presence of nZVI, and the proposed major reaction pathways based on our calculations can satisfactorily conform to the reported experimental results. The debromination preference is theoretically evaluated as meta-Br > ortho-Br > para-Br. In addition, both the calculated frontier orbital energies and adiabatic electronic affinities were found to be highly related to their experimental reductive debromination rate constants. The highest linear regression coefficient was observed in the case using the energy of lowest unoccupied molecular orbital as the molecular descriptor obtained from B3LYP/6-31G(d) (R2 = 0.961, n = 7) or B3LYP/6-31G(d,p) (R2 = 0.961, n = 7). The results clearly showed the evidence of an electron transfer mechanism associated with this reductive debromination reaction.
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20
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Wang Y, Zhou D, Wang Y, Wang L, Cang L. Automatic pH control system enhances the dechlorination of 2,4,4'-trichlorobiphenyl and extracted PCBs from contaminated soil by nanoscale Fe⁰ and Pd/Fe⁰. ENVIRONMENTAL SCIENCE AND POLLUTION RESEARCH INTERNATIONAL 2012; 19:448-457. [PMID: 21822927 DOI: 10.1007/s11356-011-0587-0] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/16/2011] [Accepted: 07/29/2011] [Indexed: 05/31/2023]
Abstract
PURPOSE Dechlorination of polychlorinated biphenyls (PCBs) by nanoscale zerovalent iron (NZVI) is often strongly hindered by increased pH because large amounts of H(+) ions were consumed during the surface reaction. The main objective of this work was to evaluate the effect of pH control in acid on the dechlorination processes of PCBs and to compare the dechlorination efficiency between 2,4,4'-trichlorobiphenyl (2,4,4'-CB) and the extracted PCBs from the field PCBs-contaminated soil in this system. METHODS The reaction solution pH was controlled to be weakly acid (4.90-5.10) with an automatic pH control system, in which the dechlorination of 2,4,4'-CB and extracted PCBs from a PCBs-contaminated soil by NZVI and palladized nanoscale zerovalent iron (NZVI/Pd) was investigated. RESULTS To control the reaction solution pH to be acid actually increased the dechlorination rate of PCBs by NZVI and NZVI/Pd. The observed normalized pseudo-first-order dechlorination rate constants (k (obs)) of 2,4,4'-CB increased from 0.0029 min(-1) (no pH control) to 0.0078 min(-1) (pH control) by NZVI and from 0.0087 min(-1) (no pH control) to 0.0108 min(-1) (pH control) by NZVI/Pd. In the case of NZVI/Pd, the chlorines in the para position were much more easily dechlorinated than ortho position, and biphenyl was the dominating product. As the solution pH was controlled at 4.90-5.10, the dechlorination rate constants of PCB congeners extracted from soil (k (obs)) were 0.0027-0.0033 min(-1) and 0.0080-0.0098 min(-1) by NZVI and NZVI/Pd, respectively. CONCLUSIONS To keep the reaction solution to be weakly acid markedly increased the dechlorination rate of PCBs, which may offer a novel technology in the remediation of PCBs-contaminated soil.
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Affiliation(s)
- Yu Wang
- Key Laboratory of Soil Environment and Pollution Remediation, Institute of Soil Science, Chinese Academy of Sciences, 71st East Beijing Road, Nanjing 210008, China
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21
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Coutts JL, Devor RW, Aitken B, Hampton MD, Quinn JW, Clausen CA, Geiger CL. The use of mechanical alloying for the preparation of palladized magnesium bimetallic particles for the remediation of PCBs. JOURNAL OF HAZARDOUS MATERIALS 2011; 192:1380-1387. [PMID: 21807459 DOI: 10.1016/j.jhazmat.2011.06.052] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/21/2010] [Revised: 04/19/2011] [Accepted: 06/20/2011] [Indexed: 05/31/2023]
Abstract
The kinetic rate of dechlorination of a polychlorinated biphenyl (PCB-151) by mechanically alloyed Mg/Pd was studied for optimization of the bimetallic system. Bimetal production was first carried out in a small-scale environment using a SPEX 8000M high-energy ball mill with 4-μm-magnesium and palladium impregnated on graphite, with optimized parameters including milling time and Pd-loading. A 5.57-g sample of bimetal containing 0.1257% Pd and ball milled for 3 min resulted in a degradation rate of 0.00176 min(-1)g(-1) catalyst as the most reactive bimetal. The process was then scaled-up, using a Red Devil 5400 Twin-Arm Paint Shaker, fitted with custom plates to hold milling canisters. Optimization parameters tested included milling time, number of ball bearings used, Pd-loading, and total bimetal mass milled. An 85-g sample of bimetal containing 0.1059% Pd and ball-milled for 23 min with 16 ball bearings yielded the most reactive bimetal with a degradation rate of 0.00122 min(-1)g(-1) catalyst. Further testing showed adsorption did not hinder extraction efficiency and that dechlorination products were only seen when using the bimetallic system, as opposed to any of its single components. The bimetallic system was also tested for its ability to degrade a second PCB congener, PCB-45, and a PCB mixture (Arochlor 1254); both contaminants were seen to degrade successfully.
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Affiliation(s)
- Janelle L Coutts
- University of Central Florida, 4000 Central Florida Blvd., Orlando, FL 32816, United States.
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22
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Zhuang Y, Ahn S, Seyfferth AL, Masue-Slowey Y, Fendorf S, Luthy RG. Dehalogenation of polybrominated diphenyl ethers and polychlorinated biphenyl by bimetallic, impregnated, and nanoscale zerovalent iron. ENVIRONMENTAL SCIENCE & TECHNOLOGY 2011; 45:4896-903. [PMID: 21557574 PMCID: PMC3122486 DOI: 10.1021/es104312h] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/07/2023]
Abstract
Nanoscale zerovalent iron particles (nZVI), bimetallic nanoparticles (nZVI/Pd), and nZVI/Pd impregnated activated carbon (nZVI/Pd-AC) composite particles were synthesized and investigated for their effectiveness to remove polybrominated diphenyl ethers (PBDEs) and/or polychlorinated biphenyls (PCBs). Palladization of nZVI promoted the dehalogenation kinetics for mono- to tri-BDEs and 2,3,4-trichlorobiphenyl (PCB 21). Compared to nZVI, the iron-normalized rate constants for nZVI/Pd were about 2-, 3-, and 4-orders of magnitude greater for tri-, di-, and mono-BDEs, respectively, with diphenyl ether as a main reaction product. The reaction kinetics and pathways suggest an H-atom transfer mechanism. The reaction pathways with nZVI/Pd favor preferential removal of para-halogens on PBDEs and PCBs. X-ray fluorescence mapping of nZVI/Pd-AC showed that Pd mainly deposits on the outer part of particles, while Fe was present throughout the activated carbon particles. While BDE 21 was sorbed onto activated carbon composites quickly, debromination was slower compared to reaction with freely dispersed nZVI/Pd. Our XPS and chemical data suggest about 7% of the total iron within the activated carbon was zerovalent, which shows the difficulty with in-situ synthesis of a significant fraction of zerovalent iron in the microporous material. Related factors that likely hinder the reaction with nZVI/Pd-AC are the heterogeneous distribution of nZVI and Pd on activated carbon and/or immobilization of hydrophobic organic contaminants at the adsorption sites thereby inhibiting contact with nZVI.
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Affiliation(s)
- Yuan Zhuang
- Department of Civil and Environmental Engineering, Stanford University, Stanford, CA 94305-4020
| | | | - Angelia L. Seyfferth
- Department of Environmental Earth System Science, Stanford University, Stanford, CA 94305-4020
| | - Yoko Masue-Slowey
- Department of Environmental Earth System Science, Stanford University, Stanford, CA 94305-4020
| | - Scott Fendorf
- Department of Environmental Earth System Science, Stanford University, Stanford, CA 94305-4020
| | - Richard G. Luthy
- Department of Civil and Environmental Engineering, Stanford University, Stanford, CA 94305-4020
- Corresponding author phone: (650) 721-2615; fax: (650) 725-9720;
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23
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Li T, Chen Y, Wan P, Fan M, Yang XJ. Chemical Degradation of Drinking Water Disinfection Byproducts by Millimeter-Sized Particles of Iron−Silicon and Magnesium−Aluminum Alloys. J Am Chem Soc 2010; 132:2500-1. [DOI: 10.1021/ja908821d] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Tianyu Li
- Department of Applied Chemistry and Department of Environmental Science and Engineering, Beijing University of Chemical Technology, Beijing 100029, China, and Department of Chemical and Petroleum Engineering, University of Wyoming, Laramie, Wyoming 82071
| | - Yongmei Chen
- Department of Applied Chemistry and Department of Environmental Science and Engineering, Beijing University of Chemical Technology, Beijing 100029, China, and Department of Chemical and Petroleum Engineering, University of Wyoming, Laramie, Wyoming 82071
| | - Pingyu Wan
- Department of Applied Chemistry and Department of Environmental Science and Engineering, Beijing University of Chemical Technology, Beijing 100029, China, and Department of Chemical and Petroleum Engineering, University of Wyoming, Laramie, Wyoming 82071
| | - Maohong Fan
- Department of Applied Chemistry and Department of Environmental Science and Engineering, Beijing University of Chemical Technology, Beijing 100029, China, and Department of Chemical and Petroleum Engineering, University of Wyoming, Laramie, Wyoming 82071
| | - X. Jin Yang
- Department of Applied Chemistry and Department of Environmental Science and Engineering, Beijing University of Chemical Technology, Beijing 100029, China, and Department of Chemical and Petroleum Engineering, University of Wyoming, Laramie, Wyoming 82071
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Smuleac V, Bachas L, Bhattacharyya D. Aqueous - Phase Synthesis of PAA in PVDF Membrane Pores for Nanoparticle Synthesis and Dichlorobiphenyl Degradation. J Memb Sci 2010; 346:310-317. [PMID: 20161475 PMCID: PMC2794051 DOI: 10.1016/j.memsci.2009.09.052] [Citation(s) in RCA: 88] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
This paper deals with bimetallic (Fe/Pd) nanoparticle synthesis inside the membrane pores and application for catalytic dechlorination of toxic organic compounds form aqueous streams. Membranes have been used as platforms for nanoparticle synthesis in order to reduce the agglomeration, encountered in solution phase synthesis which leads to a dramatic loss of reactivity. The membrane support, polyvinylidene fluoride (PVDF) was modified by in situ polymerization of acrylic acid in aqueous phase. Subsequent steps included ion exchange with Fe(2+), reduction to Fe(0) with sodium borohydride and Pd deposition. Various techniques, such as STEM, EDX, FTIR and permeability measurements, were used for membrane characterization and showed that bimetallic (Fe/Pd) nanoparticles with an average size of 20-30 nm have been incorporated inside of the PAA-coated membrane pores. The Fe/Pd-modified membranes showed a high reactivity toward a model compound, 2, 2'-dichlorobyphenyl and a strong dependence of degradation on Pd (hydrogenation catalyst) content. The use of convective flow substantially reduces the degradation time: 43% conversion of dichlorobiphenyl to biphenyl can be achieved in less than 40 s residence time. Another important aspect is the ability to regenerate and reuse the Fe/Pd bimetallic systems by washing with a solution of sodium borohydride, because the iron becomes inactivated (corroded) as the dechlorination reaction proceeds.
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Affiliation(s)
- V. Smuleac
- Department of Chemical and Materials Engineering University of Kentucky, Lexington, KY 40506
| | - L. Bachas
- Department of Chemistry University of Kentucky, Lexington, KY 40506
| | - D. Bhattacharyya
- Department of Chemical and Materials Engineering University of Kentucky, Lexington, KY 40506
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Agarwal S, Al-Abed SR, Dionysiou DD. A feasibility study on Pd/Mg application in historically contaminated sediments and PCB spiked substrates. JOURNAL OF HAZARDOUS MATERIALS 2009; 172:1156-1162. [PMID: 19709811 DOI: 10.1016/j.jhazmat.2009.07.117] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/22/2009] [Revised: 07/27/2009] [Accepted: 07/28/2009] [Indexed: 05/28/2023]
Abstract
A vast majority of literature on bimetals deals with aqueous contaminants, very little being on organics strongly adsorbed on sediments and hence very challenging to remediate. Having previously reported materials, mechanistic and parametric aspects of PCB dechlorination with Pd/Mg bimetals, here we evaluate their ability to dechlorinate (i) PCBs spiked in clean clays and sediments and (ii) historically contaminated aged sediments (Waukegan Harbor, WHS). It was determined that while water, as a medium, dechlorinated low surface area clays it was ineffective with high surface area clays and sediments. Dechlorination was governed by desorption of PCBs, hence addition of 10-25% ethanol improved dechlorination performance. Triton X-100, a surfactant, effectively desorbed PCBs from WHS but their dechlorination was not observed. Investigating possible causes, we found that while (i) Pd/Mg completely dechlorinated multi-component commercial PCB mixtures (i.e. complex PCB distribution in WHS did not limit Pd/Mg effectiveness) and (ii) active components in extraction media did not inhibit dechlorination, sulfide in WHS was poisoning Pd, compromising its activity.
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Affiliation(s)
- Shirish Agarwal
- Department of Civil and Environmental Engineering, University of Cincinnati, Cincinnati, OH 45221-0071, USA
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26
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Choi H, Al-Abed SR, Agarwal S. Catalytic role of palladium and relative reactivity of substituted chlorines during adsorption and treatment of PCBs on reactive activated carbon. ENVIRONMENTAL SCIENCE & TECHNOLOGY 2009; 43:7510-7515. [PMID: 19848169 DOI: 10.1021/es901298b] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/28/2023]
Abstract
The adsorption-mediated dechlorination of polychlorinated biphenyls (PCBs) is a unique feature of reactive activated carbon (RAC). Here, we address the RAC system, containing a tunable amount of Fe as a primary electron donor coupled with Pd as an electrochemical catalyst to potentially respond to the characteristic of contaminated sites, effectively traps and treats various PCB congeners. A dramatic increase in RAC reactivity with Pd doping at as low as 0.01% suggests its critical role for accelerating hydrodechlorination of PCBs. Characteristic adsorption and dechlorination behavior and ensuing decomposition pathways of 13 selected PCB congeners are discussed with their surface interactions with RAC. Important findings include (i) inherent dechlorination susceptibility of chlorines in para > meta > ortho position, regardless of independent or competitive conditions as well as substrate effects, (ii) favorable reduction of more toxic coplanar PCB congeners, (iii) preferential electrophilic attack to chlorines in a less substituted phenyl ring and an isolated chlorine, regardless of the steric or inductive effect as a dominant limiting factor for the dechlorination of ortho or meta PCBs, respectively, (iv) prominent dechlorination inhibition for higher ortho congeners but negligible inhibition for higher meta congeners, and (v) eventual complete dechlorination of higher PCB congeners to biphenyl.
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Affiliation(s)
- Hyeok Choi
- National Risk Management Research Laboratory, U.S. Environmental Protection Agency, 26 West Martin Luther King Drive, Cincinnati, Ohio 45268, USA
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27
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Choi H, Al-Abed SR, Agarwal S. Effects of aging and oxidation of palladized iron embedded in activated carbon on the dechlorination of 2-chlorobiphenyl. ENVIRONMENTAL SCIENCE & TECHNOLOGY 2009; 43:4137-4142. [PMID: 19569342 DOI: 10.1021/es803535b] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/28/2023]
Abstract
Reactive activated carbon (RAC) impregnated with palladized iron has been developed to effectively treat polychlorinated biphenyls (PCBs) in the environment by coupling adsorption and dechlorination of PCBs. In this study, we addressed the dechlorination reactivity and capacity of RAC toward aqueous 2-chlorobiphenyl (2-ClBP), and its aging and longevity under various oxidizing environments. RAC containing 14.4% Fe and 0.68% Pd used in this study could adsorb 122.6 mg 2-ClBP/g RAC, and dechlorinate 56.5 mg 2-ClBP/g RAC which corresponds to 12% (yield) of its estimated dechlorination capacity. Due to Fe0 oxidation to form oxide passivating layers, Fe2O3/Fe3O4 (oxide-water interface) and FeOOH/FeO (oxide-metal interface), RAC reactivity decreased progressively over aging under N2 < H2O + N2 < H2O + 02 conditions. Considering nanoscale Fe/Pd corrosion chemistry, the decline was quite slow at only 5.6%, 19.5%, and 32.5% over one year, respectively. Dissolved oxygen played a crucial role in enhancing 2-ClBP adsorption but inhibiting its dechlorination. The reactivity change could be explained with the properties of the aged RAC including surface area, Fe0 content and Fe species. During the aging and oxidation, the RAC showed limited dissolution of Fe and Pd. Finally, implementation issues regarding application of RAC system to contaminated sites are discussed.
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Affiliation(s)
- Hyeok Choi
- National Risk Management Research Laboratory, U.S. Environmental Protection Agency, 26 West Martin Luther King Drive, Cincinnati, Ohio 45268, USA
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