A ceramic electrode of ZrO2-Y2O3 for the generation of oxidant species in anodic oxidation. Assessment of the treatment of Acid Blue 29 dye in sulfate and chloride media

Abstract

A micron-sized powder of 7% mol Y2O3 stabilized ZrO2 (YSZ) was used to deposit a ceramic coating onto Ti substrate by atmospheric plasma spray. The novel YSZ ceramic presented a dense structure with cubic crystalline structure. The as-synthesized YSZ ceramic as stable anode, coupled to a stainless-steel cathode, was assessed for the anodic oxidation of Acid Blue 29 diazo dye solutions in sulfate and chloride media. The decolorization of these solutions in acidic conditions was clearly faster with chloride as electrolyte, since the generated active chlorine HClO from anodic oxidation of Clwas more powerful oxidant than ¿OH formed from water discharge at the 7YSZ surface in sulfate medium. In alkaline conditions, the loss of color was drastically reduced because of the conversion of HClO into the weaker oxidant ClO, as well as the loss of oxidation power of ¿OH, partially compensated by the increasing oxidation ability of SO4¿formed from anodic oxidation of SO42ion. The effect of other experimental variables such as current density, as well as the concentration of each electrolyte and the dye, was examined. The best experimental conditions at pH 7.0 were found for 0.050 M of electrolyte at 20 and 10 mA cm-2 using sulfate and chloride media, respectively. In contrast, lower mineralization was achieved in chloride medium because of the formation of very recalcitrant and persistent chloro-derivatives that decelerated the mineralization process. In sulfate medium, NH4+, NO3and, to much lesser extent, NO2ions were released during mineralization, whereas tartaric, maleic, acetic and oxalic acids remained in the final solution.