Enhanced dehalogenation of brominated DBPs by catalyzed electrolysis using Vitamin B 12 modified electrodes: Kinetics, mechanisms, and mass balances.

Vitamin B (VB) modified electrodes were prepared for the electrocatalytic reductive debromination of tribromoacetic acid (TBAA). Under galvanostatic conditions set as 5 mmol/L VB loading, 20 mmol/L NaSO as electrolyte, 10.0 mA/cm current density, pH 3, and 298 K, the degradation efficiency of 200 μg/L TBAA at the VB modified electrode could reach 99.9 % after 6 h. The debromination of TBAA followed the first-order kinetic model. The masses of carbon and bromine elements were conserved before and after the reaction, together with the qualitative analysis of the degradation products showed the likely degradation pathways as TBAA→dibromoacetic acid (DBAA)→monobromoacetic acid (MBAA)→acetic acid (AA). ESR detection and quenching experiments confirmed the role of atomic H* in TBAA debromination. In-situ Raman spectroscopy showed that the Co-Br bond was strongly enriched to the electrode surface, accelerating the electron transfer. The HO dissociation performance and transition states searching catalyzed by VB were calculated by Density Functional Theory (DFT) and proved that the composite electrode can effectively promote atomic H* generation. Material characterization and electrochemical performance tests showed that the VB modified electrode had excellent stability and atomic H* catalytic activity. The electrocatalytic debromination of TBAA at VB modified electrodes mainly involves two mechanisms, direct reduction by electron transfer and indirect reduction by the strongly reducing atom H*. The results provide an efficient way to achieve safe removal of brominated DBPs from drinking water after chlorination and before human consumption.