The influence of micro-/macro-structure of a boron-doped diamond electrode on the degradation of azo dye Direct Red 80

Abstract

The subject of our study involved the characterization of structurally different boron-doped diamond electrodes and their application for the treatment of model water containing azo dye Direct Red 80 in the presence of chlorides, sulfates, and their combination. The degradation pathway was proposed based on the identification of formed degradation products by a combination of liquid chromatography and high-resolution mass spectrometry (LC-HRMS) and also the determination of adsorbable organically bound halogens (AOX) in chloride-containing samples. The results show that structured silicon contributes to surface enlargement, which increases up to 10.2% and even 34.4% when combined with the structured diamond layer. While the value of electrochemically active surface area for planar electrodes ranges between 6 to 7 cm2, the area of the flow-through electrode is much larger. The highest removal rate was undoubtedly achieved on the flow-through electrode, which also showed the lowest energy consumption, corresponding to 5.9 kWh m  3, in comparison with planar electrodes, where energy consumption was approximately two times higher. Decolorization of model water over 95% was achieved in 60 min on all electrodes. Further experiments on the flow-through electrode showed a more than 90% decrease in COD in 12 h, and electrolysis in the presence of sulfates appeared to be the most economical. As the electrooxidation proceeds, the AOX levels slowly decrease. The percentage of chlorinated carbon dropped after 24 h to 4.2% in the presence of sulfates and 6% without these anions.