Photochemical transformations of 2, 6-dichlorophenol and 2-chlorophenol with superoxide ions in the atmospheric aqueous phase

The possible photochemical transformation pathways of chlorophenols (2, 6-dichlorophenol and 2chlorophenol) with superoxide anion radical (O-2(center dot-)) were studied by steady-state irradiation and 355 nm laser flash photolysis technique. O-2(center dot-) was generated by irradiating riboflavin O-2-saturated solution with an UVA light (maximum at 365 nm). The steady-state experimental results suggested that the transformation efficiency of chlorophenols improved with the increase of the initial riboflavin concentration and solution initial pH value, while the increase of chlorophenols concentration would inhibit the photochemical reaction. The second-order rate constant of the reaction of O-2(center dot-) with 2, 6-DCP phenoxyl radical (2, 6-DCP center dot) and 2-CP phenoxyl radical (2-CP center dot) were determined as (8.39 +/- 0.99) x 10(9) L mol(-1) s(-1) and (5.17 +/- 0.68) x 10(9) L mol(-1) s(-1) by laser flash photolysis techniques, respectively. The transformation of chlorophenols was accompanied by the formation of Cl- induced by superoxide radicals after the mixed riboflavin and chlorophenols solution with UVA irradiation. The main conversion products of the reaction between 2, 6-DCP and O-2(center dot-) were identified by GC-MS, as 2-chlorophenol, 2, 6-dichloro-1, 4-benzoquinone, 2, 6-dichloro-hydroquinone and 3-chlorocatechol, while 2-CP with O-2(center dot-) was 2-chloro-1, 4-benzoquinone, 2-chlorohydroquinone and phenol, respectively. The transformation pathways of 2, 6-DCP and 2-CP with O-2(center dot-) were also proposed. (C) 2022 Elsevier B.V. All rights reserved.

Automated summary

This study investigated the possible photochemical transformation pathways of chlorophenols in the presence of superoxide anion radical. The results showed that the efficiency of chlorophenols transformation increased with the initial riboflavin concentration and solution initial pH value, while higher chlorophenols concentration inhibited the photochemical reaction. The reaction rate constants and conversion products were determined using laser flash photolysis and GC-MS techniques.