Heterogeneous Catalyzed Oxidative Degradation of Indigo: A Theoretical and Experimental Study

Almost fifteen percent of the total world production of dyes is lost during the dyeing process and is released in the textile effluents. Removal of colour and organics by photocatalytic degradation is emerging as an effective treatment technique. This work presents evidence of indigo degradation through reaction with OH radicals and ozone. The reaction medium was prepared to mimic an industrial effluent, with an alkaline pH of 12, and another sample of this medium was acidified with nitric acid to pH = 2. After five hours, the first experiment showed 15.5% degradation, while for the second one it was 47%. The residual media was filtered for remove the indigo powder, and then lyophilized. The residuals of the basic medium reaction did not show IR evidence of any organic compound, while in the acid sample isatin was identified as the main product. We also report DFT computational calculations on the indigo adsorption on TiO2 surface models, and the subsequent addition reaction with OH radicals and ozone 03 reaction. Our theoretical and experimental results suggest that TiO2/UV photocatalysis could be an adequate method for treatment of wastewaters in textile industries.