Insights into bromate reduction by Fe(II): Multiple radicals generation and carbamazepine oxidation

Reduction of bromate (BrO 3 − ) by various technologies has been extensively investigated, while the fate of oxygen and bromine atoms in BrO 3 − in these processes has been largely ignored. In this study, reduction of BrO 3 − by Fe(II) ions was investigated under various conditions via electron spin resonance (ESR), laser flash photolysis (LFP), probe of phenol and quenching experiments. It was found that reduction of BrO 3 − by Fe(II) ions produced HO•, O 2 • − and reactive bromine species (eg., Br• and Br 2 • − ). HO• and O 2 • − were generated from release of one/two oxygen atoms in BrO 3 − and its reduction intermediates (BrO 2 − and BrO − ) at one time, while Br• and Br 2 • − were generated from activation of hypobromous acid by Fe(II) and reactions of HO• with formed Br − . Due to the formation of these reactive species, the tested ten organic pollutants with diverse structures can be efficiently degraded, which including carbamazepine (CBZ), ibuprofen, phenol, benzoic acid, paracetamol, bisphenol a, 4-chlorophenol, oxcarbazepine, diclofenac and sulfamethoxazole. CBZ degradation intermediates by BrO 3 − /Fe(II) system were specially identified by liquid chromatography (LC)-mass spectrometry (MS), and three pathways of hydroxylation/nitrosylation, ring contraction-amine cleavage and bromination for CBZ degradation were proposed accordingly. This study might shed new fundamental insights to bromate reduction and its implication for transformation of co-existed organic pollutants.