Electrochemical combustion of indigo at ternary oxide coated titanium anodes

Abstract

The film of iridium and tin dioxides doped with antimony (IrO₂-SnO₂–Sb₂O₅) deposited on a Ti substrate (mesh) obtained by Pechini method was used for the formation of ^·OH radicals by water discharge. Detection of ^·OH radicals was followed by the use of the N,N-dimethyl-p-nitrosoaniline (RNO) as a spin trap. The electrode surface morphology and composition was characterized by SEM-EDS. The ternary oxide coating was used for the electrochemical combustion of indigo textile dye as a model organic compound in chloride medium. Bulk electrolyses were then carried out at different volumetric flow rates under galvanostatic conditions using a filter-press flow cell. The galvanostatic tests using RNO confirmed that Ti/IrO₂-SnO₂-Sb₂O₅ favor the hydroxyl radical formation at current densities between 5 and 7 mA cm^-2, while at current density of 10 mA cm^-2 the oxygen evolution reaction occurs. The indigo was totally decolorized and mineralized via reactive oxygen species, such as (^·OH, H₂O₂, O₃ and active chlorine) formed in-situ at the Ti/IrO₂-SnO₂-Sb₂O₅ surface at volumetric flow rates between 0.1-0.4 L min^-1 and at fixed current density of 7 mA cm^-2. The mineralization of indigo carried out at 0.2 L min^-1 achieved values of 100 %, with current efficiencies of 80 % and energy consumption of 1.78 KWh m^-3.