Investigation of mechanism and kinetics in the TiO2 photocatalytic degradation of Indigo Carmine dye using radical scavengers

This study is aimed at investigating the influence of different scavenger species of radicals that might possibly be involved in the TiO 2 /UVA photocatalytic degradation of Indigo Carmine dye. The effect caused by the presence of hydroxyl radicals (1-butanol and 2-propanol), positive holes (h + ) (potassium iodide) and singlet oxygen (azide) was studied. Kinetics and optimal degradation conditions were evaluated using a factorial experiment design. The highest pseudo-first-order kinetics ( k = 5.22 × 10 −2 ± 0.002 and t 1/2 = 13.25 ± 0.49 min) was achieved at pH 4.0, 6 mg L −1 of Indigo Carmine dye and 12 mg L −1 of TiO 2 . Mineralization was not achieved, and direct photolysis was not observed under the studied conditions. Indigo Carmine degradation occurs mainly due to oxidation in the positive hole (h + ) followed by singlet oxygen action and on a smaller scale by hydroxyl radical. The use of the aforementioned radical scavengers made it possible to verify the mechanism and kinetics of Indigo Carmine dye through TiO 2 heterogeneous photocatalysis.