Comparative electrochemical degradation of the triphenylmethane dye Methyl Violet with boron-doped diamond and Pt anodes

The electrochemical degradation of the triphenylmethane dye Methyl Violet (MV) in acidic and neutral aqueous solutions has been comparatively studied in an undivided electrolytic cell containing either a boron-doped diamond (BDD) or Pt anode and a stainless steel cathode under galvanostatic conditions. The dye solutions are completely decolorized and mineralized using BDD, but both processes become much slower when using Pt. The decolorization rate always follows a pseudo-first-order kinetic equation and increases with rising current density. The effect of pH, current density and MV concentration on the degradation rate, mineralization current efficiency and energy consumption with BDD is also examined. Generated carboxylic acids such as maleic, fumaric, tartronic, formic, oxalic and oxamic are detected and quantified by ion-exclusion HPLC. These compounds persist in the electrolyzed solution with BDD nearly up to the end of the mineralization process. The nitrogen of MV is mainly lost as NO3- ion, which is more rapidly released at the final degradation stages.