Oxidation of tetrabromobisphenol A (TBBPA) by peroxymonosulfate: The role of in-situ formed HOBr

The degradation of tetrabromobisphenol A (TBBPA), one of the most widely used brominated flame retardant , was evaluated during peroxymonosulfate (PMS) oxidation. TBBPA degradation was pH-dependent, with peak degradation rate constants occurring at pH 8.0–9.0, which was distinct from some other phenolic compounds . Singlet oxygen and radicals were found to play negligible roles in TBBPA degradation. TBBPA oxidation by PMS mainly proceeded via a direct oxidation pathway and the in-situ formed HOBr was found to greatly accelerate its degradation rates. The values of species-specific second-order rate constants for the reactions of PMS with the TBBPA k HSO5 − +TBBPA , k HSO5 − +TBBPA− and k HSO 5− +TBBPA2− were determined to be (1.11 ± 0.84) × 10 −2 , (8.05 ± 2.31) × 10 −2 , and (1.34 ± 0.25) × 10 −1  M −1  s −1 , respectively, while the reaction rate constants for HOBr/OBr − with TBBPA k HOBr+TBBPA , k HOBr+TBBPA− , k HOBr+TBBPA2− and k OBr−+TBBPA2− were determined to be (9.38 ± 2.10) × 10 3 , (1.59 ± 0.56) × 10 5 , (8.22 ± 0.41) × 10 6 , and (1.81 ± 0.12) × 10 6  M −1  s −1 , respectively. The bromine mass balance analysis showed that bromide ion and HOBr/OBr − occupied 19.5% of total Br and brominated organic compounds accounted for the remaining percentages at pH 7.0. No formation of bromate was observed. Based on the identified products, a reaction pathway was proposed, which included oxidation, β-scission, hydroxylation, and dimerization reaction pathways. The results indicate that unactivated PMS is useful for the remediation of TBBPA contaminated water .