Electrochemical oxidation of C.I. Acid Red 73 wastewater using Ti/SnO2-Sb electrodes modified by carbon nanotube

Abstract

Electrochemical oxidation of C.I. Acid Red 73 (AR 73) in aqueous solution is performed in an undivided cell using Ti/SnO2-Sb-CNT as anode. Cyclic voltammetric experiments suggest that electrochemical oxidation of AR 73 is totally irreversible and direct electron transfer does not occur on anode surface. The influence of operating parameters on the degradation efficiency is investigated systematically, including current density (25–100 mA cm−2), initial dye concentration (0.5–1.5g L−1), initial pH (3–11), and different kinds of supporting electrolyte. The electrochemical degradation of AR 73 follows pseudo-first-order kinetics. The removal efficiency of AR 73 degradation increases from 78.3 to 95.7% with increased current density from 25 to 100 mA cm−2. The initial AR 73 concentration has a negative effect on degradation rates at higher value, and pH has no obvious effect on the dye removal rate. The comparative experiments using Na2SO4, NaCl, and Na3PO4 as supporting electrolyte indicate that NaCl has the most significant effect on AR 73 degradation, but shows poor mineralization ability with only 51.5% removal rate of total organic carbon. The electrogenerated oxidant S2O82- using Na2SO4 supporting electrolyte also contributes the dye degradation and mineralization compared with Na3PO4. Samples during the electrochemical oxidation process are characterized with UV–vis spectra and high performance liquid chromatography. The results show that the AR 73 and intermediates formed during the degradation are both completely removed after 3 h electrochemical oxidation. The electrochemical technique is expected to be an interesting alternative for the treatment of azo dye in wastewater.