The Radiation-induced Decoloration of Azo Dye in Aqueous Solutions

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The decoloration yield of an Acid Red 265 neutral aqueous solution, G(-Dye), equaled 1.00±0.04, regardless of the dose rate and the initial dye concentration in the early stage. The G(-Dye) increased to 1.46 in the presence of nitrous oxide, but was independent of the presence of oxygen and acetone. In nitrogen-saturated solutions, the G(–Dye) increased markedly upon the addition of alcohols—for example, up to 1.83 upon the addition of 2 mM n-butyl alcohol. On the other hand, in oxygen-saturated solutions, the G(-Dye) decreased markedly upon the addition of even a small amount of alcohols. The effects of alcohols, namely, the G(-Dye) in both the solutions were in the order of their reactivity with OH radicals. The decoloration is attributable to the attack of the OH radicals formed by the radiolysis of water to the dye. The increase in the G(-Dye) for the nitrogen-saturated solutions containing alcohols is attributable to the attack of the alcohol radicals (R\dotCHOH) formed by the reactions of alcohols with OH radicals. In the oxygen-saturated solutions, the R\dotCHOH radicals are converted to the peroxides, which do not react with the dye. The rate constant for the reaction of the OH radical with Acid Red 265, obtained by using various additives from the competition reaction method, is 9.3±1.4×109 M−1 s−1. The effects of CNS−, glucose, and phenol were also examined.
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