Synergistic effects of H\u3csub\u3e2\u3c/sub\u3eO\u3csub\u3e2\u3c/sub\u3e and S\u3csub\u3e2\u3c/sub\u3eO\u3csub\u3e8\u3c/sub\u3e\u3csup\u3e2−\u3c/sup\u3e in the gamma radiation induced degradation of congo-red dye: Kinetics and toxicities evaluation

Abstract

© 2019 Elsevier B.V. Gamma radiation has received increasing attention due to their high potential in degradation of recalcitrant pollutants. Thus in the present study, gamma radiation was used for degradation of congo-red (CR) dye, a highly toxic and carcinogenic pollutant, in the presence of H2O2 and S2O82−. The CR was significantly degraded by gamma radiation (i.e., 53%), however, presence of H2O2 and S2O82− promoted degradation of CR to 98 and 87%, respectively, at 1184 Gy absorbed dose. The radical scavengers and electron spin resonance studies revealed that gamma radiation decompose H2O2 and S2O82− into [rad]OH and SO4[rad]− and both [rad]OH and SO4[rad]− caused degradation of CR. The CR showed high reactivity, i.e., 3.25 × 109 and 8.50 × 108 M−1 s−1 with [rad]OH and SO4[rad]−, respectively, and removal of CR was inhibited in the presence of [rad]OH and SO4[rad]− scavengers. The removal of CR was promoted with elevating initial concentrations of H2O2 and S2O82− and decreasing initial concentrations of CR. pH of aqueous solution also significantly influenced removal of the dye. The proposed degradation pathways of CR were established from the [rad]OH mediated degradation of CR and nature of identified degradation products. The greater mineralization of CR, formation of small molecular mass degradation product, and decline in concentration of acetate after extended treatment suggest the gamma-ray mediated peroxide based process to be a promising alternative for potential degradation of CR