Augmented radiolytic (60Co γ) degradation of direct red 80 (Polyazo dye): optimization, reaction kinetics & G-value interpretation

Abstract

This study investigates the degradation of synthetic azo dye solution containing direct red 80 (DR-80) by high energy ionizing γ- radiation (60Co). A Box-Wilson face centered central composite design (CCF) was used with variables of pH (3.0–11.0), dose of γ-irradiation (1–6 kGy) and concentration of dye (100–500 mg/L). The predicted model was found to be significant and the predicted values are close to the experimental values with minimum residuals within the range of + 3 to − 3 limits. The concentration of dye and dose of γ-irradiation were found to be significant parameters for the degradation of DR 80. The numerically optimized model for the degradation of DR 80 showed 62.83% degradation efficiency at initial dye concentration of 500 mg/L, initial pH of 6.64 and at 3.29 kGy dose of γ-irradiation. The relation between the percentage of degradation and G values for the degradation process were also established. The synergistic effect of H2O2 on increasing the G values at lower dose of γ-irradiation was exhibited. G value increases as the concentration of H2O2 increases up to 1 mM. The degradation of DR 80 follows pseudo-first order with the dose constant (d = 0.6347 kGy−1). This study explains the importance of G value in establishing the degradation kinetics of γ-irradiation induced process.