One electron oxidation and reduction of Reactive Red-120 dye in aqueous solution: A steady state and pulse radiolysis study

The characteristics of the transient species formed in the reaction of Reactive Red-120 dye (RR-120) with selective one electron oxidants viz. N-3(center dot), Cl-2(center dot-) and selective one electron reductants viz. (CH3)(2)(COH)-O-center dot and CO2 center dot- radicals in aqueous solution were studied by pulse radiolysis technique. The rate constants for the oxidation reaction of RR-120 with N-3(center dot), Cl-2(center dot-) were determined as 1.1 x 10(9) and 1.0 x 10(8) dm(3) mol(-1) s(-1), while that of reduction reaction with (CH3)(2)(COH)-O-center dot, and CO2 center dot- radicals were obtained as 1.8 x 10(9), and 1.4 x 10(8) dm(3) mol(-1) s(-1), respectively. Lower value of the rate constant for the reaction of CO2 center dot- radicals with RR-120 is attributed due to the coulombic repulsion between the negative charges on RR-120 and CO2 center dot- radicals at pH 6.8. Steady state gamma radiolysis of aqueous solution of RR-120 dye was also investigated under the same oxidising and reducing conditions as performed in the pulse radiolysis experiment. Since the N-3(center dot) radicals are more selective one electron oxidising agent than hydroxyl radicals (OH center dot), thus more efficient decoloration was observed in the reaction of RR-120 with N-3(center dot) radicals as compared to the same with OH center dot radicals. Decoloration efficiency was found identical for the reaction of RR-120 with (CH3)(2)(COH)-O-center dot, CO2 center dot- radicals and hydrated electrons (e(aq)(-)). Transients produced in the reaction of RR-120 with e(aq)(-) may react with tert-butanol radicals and thus differ from the decay traces of the transient species produced in the reaction of RR-120 with (CH3)(2)(COH)-O-center dot radicals. Therefore, G(-dye) was observed higher for the reaction of RR-120 with e(aq)(-) than with (CH3)(2)(COH)-O-center dot radicals. (C) 2010 Elsevier Ltd. All rights reserved.