Degradation of the dye X-3B by UV/Fe(III)-generated hydroxyl radicals in aqueous solution

Abstract

Bleaching of the dye, Reactive Brilliant Red X-3B, by irradiation with light at λ≥320nm in an air-saturated aqueous solution of Fe(III) species was investigated under various conditions. It was observed that the dye, quite stable to the UV light, could be degraded efficiently when it was irradiated in the ferric solution. The initial rate degradation was almost independent of the initial [X-3B], but was greatly influenced by the initial [Fe(III)], pH, light intensity, and the anions of chloride or sulfate added to the solution. A further analysis showed that the degradation began with a simultaneous formation of ferrous ions. When all the ferric ions were transferred into Fe(II), the dye disappearance terminated no matter how much of the dye was left in the solution. The molar ratio of the Fe(II) formed to the X-3B disappeared was evaluated to be over 3, depending on the yield of the dye degradation. The result suggests that the process is initiated by the photolysis of Fe(III)-hydroxy species, from which the hydroxyl radicals are generated to oxidize the dye substrate subsequently.