Electro-catalytic degradation of phenol on several metal-oxide anodes

Abstract

Three kinds of Ti-based multilayer metal-oxide electrode, including Ti/SnO 2 + Sb 2O 3/PbO 2, Ti/SnO 2 + Sb 2O 3/MnO x and Ti/SnO 2 + Sb 2O 3/RuO 2 + PbO 2 electrodes, were prepared by thermal decomposition, and SnO 2 + Sb 2O 3 coatings were produced with a polymeric precursor method (PPM). The conversion of phenol was carried out with these electrodes as anodes under galvanostatic control. Samples during the electrolyses were characterized with UV–vis spectra and chromatography, and chemical oxygen demand (COD) and instantaneous current efficiency (ICE) for phenol degradation were also determined. The results show that phenol can be oxidized and degraded for all of the three anodes, and the oxidation reactions of phenol follow first-order kinetics, but there are considerable differences in the effectiveness and performance of electro-catalytic degradation. Phenol can be degraded relatively fast on the Ti/SnO 2 + Sb 2O 3/PbO 2 anode and the degradation rate of phenol is slower with the Ti/SnO 2 + Sb 2O 3/MnO x electrode, and the slowest with the Ti/SnO 2 + Sb 2O 3/RuO 2 + PbO 2 electrode, whose apparent rate constants are 2.49 × 10 −2, 1.42 × 10 −2 and 9.76 × 10 −3 min −1, respectively. The rates of electro-catalytic degradation relate to oxygen evolution potential, and the higher the oxygen evolution potential, the better the performance of electro-catalytic degradation. The potential for oxygen evolution at the Ti/SnO 2 + Sb 2O 3/PbO 2 anode is highest, then Ti/SnO 2 + Sb 2O 3/MnO x , following Ti/SnO 2 + Sb 2O 3/RuO 2 + PbO 2. The accelerated life tests at 60 °C and in 1.0 mol L −1 aqueous H 2SO 4 with an anodic current density of 4.0 A cm −2 show that the service life is prolonged when the SnO 2 + Sb 2O 3 interlayer coating are inserted between Ti substrate and active layers.