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

Reduction of bromate (BrO3−) by various technologies has been extensively investigated, while the fate of oxygen and bromine atoms in BrO3− in these processes has been largely ignored. In this study, reduction of BrO3− 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 BrO3− by Fe(II) ions produced HO•, O2•− and reactive bromine species (eg., Br• and Br2•−). HO• and O2•− were generated from release of one/two oxygen atoms in BrO3− and its reduction intermediates (BrO2− and BrO−) at one time, while Br• and Br2•− 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 BrO3−/Fe(II) system were specially identified by liquid chromatography (LC)-mass spectrometry (MS), and three pathways of hydroxylation, 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.