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论文类型：期刊论文

发表时间：2014-01-01

发表刊物：CHEMOSPHERE

收录刊物：SCIE、EI、PubMed

卷号：95

页面范围：200-205

ISSN号：0045-6535

关键字：Polychlorinated biphenyls; TDDFT; Photodechlorination; Photoproduct; Pathway

摘要：Photodechlorination is a key process affecting the fate and effect of polychlorinated biphenyls (PCBs) in the environment. However, there are still numerous gaps in our knowledge, which become apparent in photodechlorination mechanism of PCBs. We investigated the conformations of 35 PCB congeners in the ground state and the first triplet excited state (T-1), and predicted the photodechlorination pathway of the PCBs by calculating bond dissociation energies of the C-Cl bonds and activation energies of the C-Cl bond dissociation in the excited T-1 state. Results show that the torsional degree of the two benzene rings of the PCBs depends on the number of ortho chlorines because of steric effect in the ground state. The two benzene rings of the PCBs with low photoreactivity tend to be coplanar and their torsional degree becomes lower in the excited T-1 state compared with those in the ground state. The serious deformation and non-coplane of the benzene rings of some PCBs (e.g. PCB138) in the excited T-1 state reduces the conjugation between the two benzene rings, implying that these PCBs have high photoreactivity. The dissociation of the C-Cl bond is the rate-determining step in the photodechlorination reactions of PCBs when the hydrogen donor is methanol. The main photodechlorination pathways predicted in this study are in good agreement with previous experimental results. Our results have provided new insights into mechanism of PCBs photodechlorination, which could be useful in the future in utilizing quantum chemistry calculation in investigating the environmental behavior and fate of organic pollutants. (C) 2013 Elsevier Ltd. All rights reserved.