Unprecedented formation of reactive BrO- ions and their role as mediators for organic compounds degradation: The fate of bromide ions released during the anodic oxidation of Bromophenol blue dye

Based on the existing literature, active chlorine-mediated electrochemical oxidation has been extensively studied when Cl- is added or Cl- is already present in the water matrices, as well as when Cl- is released from the target organic pollutants during their degradation. However, no attempts have been published concerning the fate and role of bromide (Br-) ions released during the anodic oxidation (AO) of organobromine compounds. Therefore, the AO of bromophenol blue dye (BPB) was investigated in a parallel plate flow reactor using a boron-doped diamond (BDD) anode. The effect of the applied current on the color removal efficiency and mineralization of BPB solution was examined and compared with AO of phenol red (PR) which has a similar molecular structure to BPB (but without Br) in order to understand the role of Br heteroatoms on the mineralization of BPB. Faster and higher mineralization and discoloration were achieved when treated with BPB solution compared to PR under similar experimental conditions. This behavior was associated with the electrogeneration of BrO-, from the heteroatom Br which is released as the bromide ion (Br-), during the degradation of BPB. The active bromine species are formed via direct and indirect oxidation approaches which were proposed based on ion chromatography and linear scanning voltammetry analysis. Unexpected autoelectrocatalytic reaction: The degradation and mineralization of bromophenol blue (BPB) dye is initiated by heterogeneous free center dot OH mediation, with the release of Br- electro(chemical)-transformed to secondary oxidants (BrO-), which can oxidize both the parent BPB molecules and other easily oxidizable byproducts.image