Electrocatalytic dechlorination of aqueous trichloroacetic acid by Vitamin B12 modified iron electrode

Abstract

Haloacetic acids (HAAs) are ubiquitously detected in drinking water and even persistent after boiling due to their stability and nonvolatility, which leads to risk exposure to human. To minimize the risk, HAAs removal through electrocatalytic reduction easily utilized in point-of-use household devices is proposed. Trichloroacetic acid (TCAA) as a typical target, was investigated using laboratory-prepared metal electrode modified with Vitamin B12 (VB12) by the drop coating method. The dechlorination performance and effects of influencing factors on the TCAA dechlorination by VB12/metal composite cathode were studied. Under the conditions of 10.0 mg VB12 loading and 7.0 mA/cm2 current density, 92.9% TCAA removal efficiency was achieved within 5 h at 25 °C in neutral water solution. The degradation processes followed the first-order kinetic model. The results show that VB12/iron (Fe) electrode presented the superior electrocatalytic activity than VB12/aluminium and VB12/copper. The dechlorination efficiency of TCAA was promoted by higher VB12 loadings and current density; inhibited by alkaline condition and higher initial concentration of TCAA. The synergistic effect between atomic H* and VB12 occurred during the TCAA dechlorination process through the electron transfer. The proposed pathway elucidated that TCAA was dechlorinated to form dichloroacetic acid (DCAA) and monochloroacetic acid (MCAA), with acetic acid and chloride as ultimate products. This electrocatalysis system with VB12/Fe composite electrode exhibits high reaction efficiency, targeted dehalogenation, and environmental friendliness. This work is expected to provides a new way for the removal of halogenated DBPs at the tap and the safeguard drinking water for consumers.