Kinetic modeling of the radiolytic degradation of Acid Orange 7 in aqueous solutions.

The degradation of Acid Orange 7 (AO7) in aqueous solutions induced by gamma-ray irradiation was investigated in terms of both the disappearance of parent molecule (decoloration) and the degree of mineralization. The disappearance of AO7 followed pseudo first-order kinetics, whereas its mineralization could be described by zero-order kinetics. The pseudo first-order degradation rate constants were found to be proportional to irradiation dose rates and the reciprocals of initial AO7 concentrations. Based on the experimental results and a reaction analysis on the steady-state radiolysis of aerated aqueous solutions, a kinetic model was developed for describing the radiolytic degradation of AO7. Moreover, with this kinetic model, the reaction rate constants of e(aq)(-) and H. with AO7 were estimated as 3.0 x 10(9) and 8.4 x 10(9) x L mol(-1) s(-1), respectively. Taking the relative contributions of oxidative and reductive species to AO7 degradation into account, oxidative radiolysis proved to be a better approach for the degradation of AO7.