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A DFT/TDDFT study on the mechanisms of direct and indirect photodegradation of tetrabromobisphenol A in water

Author:
Wang, Se, Wang, Zhuang, Hao, Ce, Peijnenburg, Willie J.G.M.
Source:
Chemosphere 2019 v.220 pp. 40-46
ISSN:
0045-6535
Subject:
cyclization reactions, density functional theory, endothermy, flame retardants, geometry, heat production, hydroxyl radicals, photolysis, risk assessment, singlet oxygen
Abstract:
Tetrabromobisphenol A (TBBPA) is the most widely used commercial brominated flame retardant. However, the mechanisms underlying the photodegradation of TBBPA remain unclear. Here we use density functional theory and time-dependent density functional theory to examine the photodegradation of the two species of TBBPA in water: TBBPA (neutral form) and TBBPA− (anionic form). The study includes direct photodegradation and indirect photodegradation of TBBPA with ·OH and 1O2. The results of the calculations indicate that indirect photodegradation of TBBPA and TBBPA− with ·OH occurs via OH-addition and Br-substitution. All of the OH-addition and Br-substitution pathways are exothermic. Indirect photodegradation of TBBPA and TBBPA− by 1O2 proceeds via H abstraction by 1O2.Ea was higher for H abstraction of TBBPA than H abstraction of TBBPA−. The mechanisms for the direct photodegradation of TBBPA and TBBPA− include debromination, C1C7/C7C13 cleavage, and cyclization. CBr cleavage was observed in the optimized geometries of TBBPA and TBBPA− at the lowest excited triplet state. However, high Ea values and an endothermic nature indicated that C1C7/C7C13 cleavage and cyclization reactions were not the main pathways. OH-adducts, Br-substitution products, H-abstraction (by 1O2) products, and debromination products were the main products of photodegradation of TBBPA. These findings provide useful information for risk assessment and pollution control of brominated flame retardants.
Agid:
6257858