[Formation of Halogenated By-products in Co²⁺ Activated Peroxymonosulfate Oxidation Process]

Sulfate radicals (SO₄·⁻) generated by Co²⁺ catalyzed activation of peroxymonosulfate (PMS) are highly oxidative and can be applied to degrade various organic pollutants. It was revealed in this research that bromide could be transformed in this process to reactive bromine species which reacted with phenol subsequently, leading to the formation of bromophenols and brominated by-products such as bromoform and dibromoacetic acid. The formation of the brominated by-products first increased and then decreased. The maximum yields of bromoform (10.3 µmol · L⁻¹) and dibromoacetic acid (14.6 µmol · L⁻¹) occurred at approximately 8 h with initial phenol, PMS, Br⁻, Co²⁺, concentrations of 0.05, 1.0, 0.2, and 5 µmol · L⁻¹, respectively. Formation of the brominated by-products decreased with increasing pH. With constant total halides, increasing Cl⁻/Br⁻ ratio decreased the total formation of halogenated by- products but generated more chlorinated byproducts. The findings of this research can provide valuable information in assessing the feasibility of SO₄·⁻ based oxidation technologies in real practice.