Formation of brominated and nitrated byproducts during unactivated peroxymonosulfate oxidation of phenol

Brominated and nitrated byproducts generated from bromide (Br - ) and nitrite (NO 2 - ), respectively, by sulfate radical (SO 4 •- ) oxidation have raised increasing concern. However, little is known about the concurrent generation of brominated and nitrated byproducts in the unactivated peroxymonosulfate (PMS) oxidation process. This study revealed that Br - can facilitate the transformation of NO 2 - to nitrated byproducts during unactivated PMS oxidation of phenol . In the co-existence of 0.1 mM Br - and 0.5 mM NO 2 - , the total yield of identified nitrated byproducts reached 2.316 μM in 20 min, while none was found with NO 2 - alone. Nitryl bromide (BrNO 2 ) as the primary nitrating agent was formed via the reaction of NO 2 - with free bromine in situ generated through the oxidation of Br - by PMS. BrNO 2 rapidly reacted with phenol or bromophenols , generating highly toxic nitrophenols or nitrated bromophenols, respectively. Increasing NO 2 - concentration led to more nitrated byproducts but less brominated byproducts. This study advances our understanding of the transformation of Br - and NO 2 - in the unactivated PMS oxidation process. It also provides important insights into the potentially underestimated environmental risks when PMS is applied to degrade organic contaminants under realistic environments, particularly when Br - and NO 2 - co-exist.