Degradation/decoloration of concentrated solutions of Orange II. Kinetics and quantum yield for sunlight induced reactions via Fenton type reagents

Light and thermal processes involving Fenton reagent are shown to be effective in the mineralization/decoloration of concentrated Orange II solutions. Light activation accelerates the observed degradation and the UV component of natural sunlight is sufficient to promote the reaction leading to the ate-dye abatement. The degradation involves dark and light steps. Kinetic information on these steps is reported. The results obtained in this study suggests that the thermodynamic potential for the redox couple in a Fenton-like reagent is not the most important factor controlling ther degradation of this dye. A quantum yield of 0.10 was observed for Orange II disappearance. Decoloration of a 2.9 mM dye solution (450 mg Cl-1) is achieved in less than 2 h via photo-Fenton reactions and mineralization is completed to 95% in less than 8 h. A turnover number of 4.7 was estimated for light induced processes in the model system used. Cyanuric acid added to the Fenton system suggests that besides the OH radicals, highly stable Fe-complexes in combination with H2O2 are active in the abatement of this ate-dye. Near surface radical formation is shown to be important during the observed photocatalysis. No activation energy was detected during the mineralization suggesting a radical mechanism for this reaction. The quantum yields observed as a function of wavelength during Orange II disappearance corresponds in experimental error to the point-by-point addition of the absorbance of the Fe3+ and H2O2 solutions used in the photolysis.