Application of Ti/Pt/beta-PbO2 Anodes in the Degradation of DR80 Azo Dye

This study describes the application of a Ti/Pt/PbO2 electrode as photoanode in the degradation of the dye Direct Red 80 (DR80). The electrode was prepared by platinization of a titanium substrate, followed by electrodeposition of a PbO2 layer. The presence of beta-PbO2 phase was confirmed by X-ray diffraction. DR80 degradation tests were performed by different techniques, namely, photolysis, photocatalysis, electrocatalysis and photoelectrocatalysis. The best colour removals were obtained in the photoelectrocatalysis assays and were higher than 85% for 5.0 and 12.5 mg L-1 dye initial concentration and about 72% for 25.0 mg L-1 DR80 initial concentration, after applying a current intensity of 5 mA for 6 hours. At a DR80 initial concentration of 25.0 mg L-1, the best absorbance removals were obtained in the photoelectrocatalytic assays, with a current intensity of 50 mA, which led to a colour removal of 100% after 4 hours. Photolysis and photocatalysis presented similar colour removals that were 62, 26 and 18% for the initial concentrations of 5, 12.5 and 25 mg L-1, respectively.