Dechlorination of chloroacetic acids by electrocatalytic reduction using activated silver electrodes in aqueous solutions of different pH

Chloroacetic acids (CAAs, including trichloroacetic acid, dichloroacetic acid and monochloroacetic acid) are byproducts formed upon the addition of chlorine to water for disinfection purpose and they pose a potential human health risk. To catalyze the dechlorination of CAAs, an activated silver electrode was prepared by an oxidation–reduction cycle process. Surface structure and roughness factor of the activated silver electrode and its catalytic activity (including stability) towards the dechlorination of CAAs in aqueous solutions of different pH were studied by SEM, underpotential deposition (UPD) method, cyclic voltammetry (CV) and controlled-current electrolysis, respectively. Experimental evidence is presented that the activated silver electrode, having a porous surface with a roughness factor of approx. 63.9, is an excellent electrocatalytic material for direct dechlorination of CAAs and the complete dechlorination of trichloroacetic acid to safe acetic acid with excellent current efficiency (near 95%) can be successfully achieved by using this peculiar electrode in alkaline aqueous solutions. The reduction of trichloroacetic acid in a stepwise dechlorination fashion was suggested and trichloroacetic acid (TCAA) → dichloroacetic acid (DCAA) → monochloroacetic acid (MCAA) → acetic acid (AA) probably is the main reductive reaction route independent of pH.