Abstract
An investigation was conducted into the reaction selectivity of azo dye decoloration by peroxidase (POD). The effects of pH and the addition of p-iodophenol on decoloration rate were investigated using 3 types of dye in single-dye and mixed-dye systems. The addition of p-iodophenol accelerated decoloration. In the mixed-dye system, a pH of 8.0 resulted in the highest decoloration rate. HPLC was used to determine the decoloration rate of individual dyes in the mixed-dye system. The decoloration reaction of Orange I proceeded swiftly, decoloration of Orange II was slowed, and decoloration of Orange G was accelerated. The reaction mechanism in the mixed-dye system is considered to be as follows. Orange I reacts much faster than the other dyes, producing radicals immediately after the reaction commences and then decomposing. Meanwhile, since Orange II has a higher oxidation potential than Orange I, the reaction between Orange II and POD begins after completion of the Orange I reaction. The reaction with Orange G, which has a higher oxidation potential than Orange II, commences even later. Some of the Orange II radicals produced undergo radical reactions with Orange G, transferring electrons to Orange G and reverting to Orange II. As a result, the Orange II reaction is inhibited more than in an Orange II-only system. Conversely, when p-iodophenol was introduced into the mixed-dye system, the reaction selectivity was lost as p-iodophenol radicals reacted simultaneously with all 3 dyes.
