Enhanced deep dehalogenation of brominated DBPs on vitamin B12 composite electrodes by the synergistic effect of UV irradiation: Accelerated formation of Co-Br bonds and enhanced mediation by atomic H*

Complete dehalogenation of halogenated organic pollutants has attracted increasing attention, and electrocatalytic reduction processes are considered prospective technologies due to their high selectivity for carbonhalogen bonds. In this study, a vitamin B12 (VB12) composite electrode was prepared and applied to remove the refractory tribromoacetic acid (TBAA). The reduction process dominated by the VB12 composite electrode showed a degradation efficiency of 55.2 % for 200 mu g/L TBAA within 60 min. Interestingly, UV irradiation considerably increased the efficiency of TBAA for dehalogenation on the VB12 composite electrode. The photoelectrochemical co-catalytic system of a VB12 composite electrode coupled with UV (LP UV 254 nm) could remove 92.2 % of TBAA in 20 min with a rate constant 12 times higher than the VB12-only electrolysis system. The in situ Raman characterization and cyclic voltammetry tests confirmed that the accelerated formation of CoBr bonds and the enhanced atomic H* mediated ability were responsible for improving debromination efficiency. The degradation of TBAA mainly underwent chemical reactions of debromination and mineralization. Acetic acid, formic acid, formaldehyde, and Br- were the major transformation products of TBAA. Acidic conditions favoured TBAA removal in the UV synergistic VB12 electrolytic system, and excellent cycling stability of debromination was obtained in complex aqueous environments (actual bodies of water containing various inorganic and organic matter). This research provides an efficient dehalogenation technology for halogenated micropollutants and novel perspectives on the scientific design of photoelectrochemical dehalogenation processes.