Fundamental Study on Electrochemical Dechlorination of Dioxins

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Chlorobenzene constitutes the parts of dioxins. Studying active electrodes for dechlorination of chlorobenzene will lead to the development of electro-catalysts for transforming dioxins to harmless materials. Electrochemical dechlorination of chlorobenzene was studied using voltammograms and macro electrolysis in acetonitrile solution containing 0.1 M TEAP and mediators. Electrodes examined were Pt, Ir, Rh, Pd, Au, Ag, Zn, In, Pb, Sn, Cu, Fe, and Cd. Naphthalene, dibenzofuran, anthracene and perylene were adopted as mediators. Voltammograms in the solution containing chlorobenzene and naphthalene gave a peak arising from the reduction of chlorobenzene on the electrodes of which overpotentials for hydrogen evolution are high. The following order was obtained for the reduction current : Cd < Sn < In < Pb < Zn < Ag. The other electrodes gave no current due to the reduction of chlorobenzene, because the current due to the hydrogen evolution overwhelmed the reduction current. Dibenzofuran gave the same results as naphthalene, whereas anthracene and perylene had no activity for the reduction of chlorobenzene.We did macro electrolysis on Ag, Zn and Pt electrodes at -2.8 V (Ag/Ag^+) in 0.1 M TEAP/acetonitrile containing 10 mM of chlorobenzene and naphthalene. The main product was benzene on all the electrodes : current efficiency of benzene was 38% for Pt, 86% for Ag and Zn, respectively. Another reduction product was hydrogen. The partial current density of Ag was highest of all, 12.4 mA/cm^2. This value is more than 5 times as high as the former report using C electrode and dibenzofuran. The combination of Ag electrode and naphthalene has the high activity for the dechlorination of chlorobenzene.