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. N3, Cl2− and selective one electron reductants viz. (CH3)2COH and CO2− radicals in aqueous solution were studied by pulse radiolysis technique. The rate constants for the oxidation reaction of RR-120 with N3, Cl2− were determined as 1.1×109 and 1.0×108 dm3 mol−1 s−1, while that of reduction reaction with (CH3)2COH, and CO2− radicals were obtained as 1.8×109, and 1.4×108 dm3 mol−1 s−1, respectively. Lower value of the rate constant for the reaction of CO2− radicals with RR-120 is attributed due to the coulombic repulsion between the negative charges on RR-120 and CO2− 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 N3 radicals are more selective one electron oxidising agent than hydroxyl radicals (OH), thus more efficient decoloration was observed in the reaction of RR-120 with N3 radicals as compared to the same with OH radicals. Decoloration efficiency was found identical for the reaction of RR-120 with (CH3)2COH, CO2− radicals and hydrated electrons (eaq−). Transients produced in the reaction of RR-120 with eaq− 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)2COH radicals. Therefore, G  (-dye) was observed higher for the reaction of RR-120 with eaq− than with (CH3)2COH radicals.