The peculiar role of iodides and formation of iodinated oligomer byproducts upon phenol mineralization with boron-doped diamond anode

Abstract

Formation of halogenated aromatic byproducts upon electrochemical advanced oxidation processes (EAOPs) had attracted increasing concerns in recent years. However, previous correlative works mainly focused on the generation of chlorinated and brominated byproducts, and the works concerning iodinated byproducts were still missing. Herein, this research was designed to investigate the generation of iodinated aromatic byproducts (IABs) during phenol electrochemical degradation with boron-doped diamond (BDD) anode. Firstly, response surface methodology was employed to compare the effects of major operating parameters on the mineralization efficiency, and the peculiar role of iodide ions was thus identified. Next, LC/MS analysis was conducted to identify the iodinated organic byproducts. Twenty-six major IABs were identified with NaI as electrolyte, including p-iodinated phenol, 2,4-diiodophenol, and iodinated dimers and trimers with complex ether structures. These findings confirmed the critical role of active iodine species during the electrolytic oxidations, as well as the overlooked coupling reactions between iodinated phenoxy radicals. Lastly, the structural characteristics of iodinated oligomers had been compared with those of chlorinated and brominated ones. Since IABs were more genotoxic than their chlorinated and brominated analogues, their formations should be carefully treated when EAOPs were applied in environmental matrices containing free iodide ions.