The Effect of NCS− on the Radiation-induced Decoloration of Azo and Anthraquinone Dyes in N2O-saturated Aqueous Solutions

Abstract

Abstract The radiation-induced decoloration of azo and anthraquinone dyes was studied in N2O-saturated aqueous solutions containing NCS−. In the N2O-saturated solutions, the decoloration yield, G(–Dye), increased markedly upon the addition of NCS−, which is an efficient scavenger of the OH radical—that is, from 1.46 up to 2.10 for Acid Red 265 and from 0.51 up to 1.51 for Acid Blue 40 upon the addition of 1 mM NCS−. In the nitrogen-saturated solutions, however, the G(–Dye) decreased upon the addition of NCS−. It is concluded that the increase in the G(–Dye) upon the addition of NCS− in the N2O-saturated solutions is mainly attributable to the attack of the radical anion (NCS)2− on the ring structure of the dyes. This radical anion is formed through the following path: NCS−+OH→NCS+OH− and NCS+NCS−\ightleftarrows(NCS)2−. At low NCS− concentrations, the G(–Dye) decreased for Acid Red 265 and increased for Acid Blue 40. This may be attributable to the larger reactivity of (NCS)2− on Acid Blue 40 than on Acid Red 265.