Photochemical degradation and debromination of bromophenols: Overlooked role of hydrated electron

Photolysis and debromination of bromophenols were widely investigated previously. However, the role of reactive species especially hydrated electrons (e aq − ) in their degradation was overlooked. Therefore, in the study, generation and role of the reactive species generated during the photolysis of bromophenols were identified and evaluated by using 2,4,6-tribromophenol (TBP) as a model at different pH values from 4 to 11 under anaerobic condition. It was found that photolysis of TBP solution under UV irradiation (254 nm) yielded organic radicals (C•), hydrogen radicals (H•) and e aq − . By using nitrite and monochloroacetic acid (MCAA) as scavengers of H•/e aq − , the role of UV direct photolysis, H• and e aq − in degradation of TBP was quantitatively assessed at different initial pH (pH 0 ) values. UV irradiation induced direct photolysis of TBP was mainly dependent on its molar absorbance coefficient (ε) at 254 nm. Contribution rate of UV irradiation to degradation of TBP was about 60% at pH 0 4, 7 and 11. Interestingly, the contribution rate of e aq − was high as 35.8%-40% at pH 0 4–11, while the contribution rate of H• was negligible (<2.5%) at these pH values. Accordingly, UV and e aq − induced degradation and debromination pathways of TBP under UV irradiation were proposed. This work gains deep insight into the photolysis process of bromophenols, and clarifies the important role of e aq − in photo-degradation of bromophenols.