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

Abstract

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 kHSO5−+TBBPA, kHSO5−+TBBPA− and kHSO5−+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 kHOBr+TBBPA, kHOBr+TBBPA−, kHOBr+TBBPA2−and kOBr−+TBBPA2− were determined to be (9.38 ± 2.10) × 103, (1.59 ± 0.56) × 105, (8.22 ± 0.41) × 106, and (1.81 ± 0.12) × 106 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.