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Indexed by:期刊论文

Date of Publication:2014-08-15

Journal:COMPUTATIONAL AND THEORETICAL CHEMISTRY

Included Journals:SCIE、Scopus

Volume:1042

Page Number:49-56

ISSN No.:2210-271X

Key Words:PCDD/Fs; PBDD/Fs; Photodehalogenation; DFT; TDDFT; Mg2+

Abstract:Quantum chemical calculations studies were performed to investigate the underlying photodehalogenation mechanisms of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) and polybrominated dibenzo-p-dioxins and dibenzofurans (PBDD/Fs), as well as Mg2+ effects. The bond dissociation energies of C-Cl/Br bonds, electronic absorption spectra, vibrational frequencies, and NBO charges of PCDD/Fs and PBDD/Fs were calculated by density functional theory and time-dependent density functional theory. Results show that the photodehalogenation reactivity of PCDD/Fs and PBDD/Fs increases with an increase of halogenation degree. Halogen atoms attached to the benzene ring with more halogens substituted have higher photoreactivity. For PCDD/BDDs, the photoreactivity of halogens at 2 and 3 positions are higher than that of halogens at 1 and 4 positions. For PCDF/BDFs without halogen substitution at 9 position, the order of photoreactivity of halogens follows: 2, 3 > 1, 4 position. However, for PCDFs/BDFs with halogen substitutions at 1 and 9 positions, the order of photoreactivity of Cl/Br atoms follows: 1 > 2 > 3 > 4 position. 1,2,3,4,6,7,9-H7CDD/BDD has been predicted to be the main photodehalogenation products of O8CDD/BDD. However, by the presence of Mg2+, the bond dissociation energies of C Cl/Br bonds of O8CDD/BDD at 4 and 6 positions are drastically reduced and the main photodehalogenation products are changed to 1,2,3,4,6,7,8-H7CDD/BDD. Furthermore, the presence of Mg2+ significantly reduces the bond dissociation energies of C-Cl/Br bonds of O8CDF/BDF at 4 and 6 positions, but has no effects on the main photodehalogenation products. These findings provide an insight into the evaluation and prediction of photochemical behavior of persistent organic pollutants. (C) 2014 Elsevier B.V. All rights reserved.