Photo-electrocatalytic degradation of azo dye and evaluation of the electricity generation by using a visible light active CNT-TiO2-BiOBr-Bi2S3 electrode

Abstract

This study presents a promising technology for the degradation of azo dye (Acid black 172 (AB 172)) using a modified TiO2 anode. CNT-TiO2-BiOBr-Bi2S3 was synthesized and deposited on the anode electrode, and a graphite sheet was selected as the cathode in a photoelectrochemical oxidation process. The CNT-TiO2-BiOBr-Bi2S3 composite photocatalyst significantly advances visible light-driven photocatalytic systems, outperforming conventional catalysts due to synergistic interactions among its components. The morphology, chemical composition, and optical properties of the CNT-TiO2-BiOBr-Bi2S3 catalyst were investigated by XRD, FTIR, FESEM, EDX, PL, and UV–Vis analyses, respectively. The effects of the processing factors and their statistical optimization values were determined using response surface methodology. The results showed that increasing the light intensity and irradiation time enhanced the photoelectrochemical degradation of the azo dye. In contrast, increasing the dye concentration leads to a decrease in degradation efficiency and COD removal. The acidic medium is beneficial in improving the removal efficiency of AB 172. Complete removal of AB 172 was achieved under optimal degradation parameters, including pH = 4, an AB 172 concentration of 15 mg/L, an irradiation time of 7 h, and a light intensity of 500 lm. COD removal and current density were about 90% and 200 µA, respectively, under optimal conditions. The anode and cathode reusability were examined, showing that the photoelectrochemical process effectively degrades contaminants, even after four electrode reuse cycles. This study demonstrates the potential of using reusable CNT-TiO2-BiOBr-Bi2S3 electrodes for visible light-responsive and sustainable water and wastewater treatment technology. © The Author(s), under exclusive licence to the Institute of Chemistry, Slovak Academy of Sciences 2025.