Electrochemical oxidation of trans-3,4-dihydroxycinnamic acid at PbO2 electrodes: direct electrolysis and ozone mediated reactions compared

A comparative study of the oxidative degradation of trans-3,4-dihydroxycinn amic acid was carried out using three different methods, two of which have in common the use of electrogenerated ozone as a potential oxidant: (i) dir ect electrolysis; (ii) external cell chemical reactions with O-3; and (iii) a 'cathodic oxidation' in which an O-2/O-3 mixture is fed into the cathodi c compartment containing the organic substrate; H2O2 produced reacts with o zone to yield radicals that bring about the demolition of the organic compo und. The nature products formed by the direct electrochemical oxidation dep ends on potential. The degradation of dihydroxy-acid is observed only at re latively high potentials, where radical oxygen species are formed ill a hig h amount by the oxidation of water. At relatively lower potentials the proc ess shows stirring dependence and leads essentially to one oxidation produc t which is adsorbed on the electrode. A comparative examination of the resu lts, considering also the requested amount of ozone as a parameter, shows t hat the external cell and cathodic oxidation are the most efficient methods . This confirms our previous data on the oxidation of phenolic compounds, a nd the cathodic oxidation with ozone emerges as a promising approach in the abatement of pollutants. (C) 2000 Elsevier Science Ltd. All rights reserve d.