Synthesis and characterization of Sb2O5-doped Ti/SnO2-IrO2 anodes toward efficient degradation tannery dyes by in situ generated oxidizing species

Nowadays, the increasing pollution of natural water effluents with textile dyes is an emerging problem that has not received attention enough. This work presents a study on the preparation of two Ti/IrO2-SnO2-Sb2O5 electrodes so-called E1 and E2 with 0.01 and 0.09 wt% of Sb dopant, respectively, by the Pechini method. The characteristics of these electrodes were analyzed by scanning electron microscopy-energy dispersive X-ray spectroscopy and X-ray diffraction. The E2 anode possessed a higher electroactivity and produced more largely hydroxyl radicals in electrochemical oxidation (EO). The action of this oxidant, along with active chlorine of textile dyes like Violet RL, Green A and Brown DR was assessed in 50 mM Na2SO4 and 10 mM NaCl at pH 3.0 by EO with the E2 anode. It was found that the discoloration of 80 mg L−1 of each individual solution was enhanced with increasing the current density from 25 to 50 mA cm−2, always obeying a pseudo-first-order kinetics. The process was faster in the sequence: Green A < Brown DR < Violet RL, and at 50 mA cm−2, a loss of color > 86% of color was attained in only 6 min. A mixture with 80 mg L−1 of each dye was treated under analogous EO conditions, giving rise to 100% discoloration in 20 min and about 90% chemical oxygen demand removal in 60 min at 50 mA cm−2. Three carboxylic acids, maleic, oxalic and oxamic, were detected as final byproducts by ion-exclusion high-performance liquid chromatography. The results reported in this work demonstrate the large effectiveness of the synthesized Ti/IrO2-SnO2-Sb2O5 electrodes to remove textile azo dyes, with higher rate constants than usual anodes.