Modeling of photodecoloration of azo dye in a cocktail photolysis system

The modeling of photodecoloration of a nonbiodegradable azo dye, Reactive Red 2 (RR2), in a cocktail mixture of acetone (ACE) and triethylamine (TEA) solution, was investigated. It was found that the cocktail photolysis system was capable of completely decolorizing the azo dye in a very short treatment time, and the overall dye degradation followed pseudo-first-order decay kinetic. Three distinct stages were observed in the cocktail photolysis profiles. A lag phase was observed at the commencement of the degradation, but its duration was gradually reduced with the increment of the TEA concentration and the incident light intensity. Subsequently, a fast decay of RR2 was observed, in which over 80% of the dyes were reduced and it was interesting to find a tailing stage after 90-95% of the color was removed. A quantitative estimation of RR2 in the cocktail photolysis system was also studied. The differential equation consisting of two parallel reactions was solved to predict the concentration of RR2 at any reaction time with very good agreements. Furthermore, the sensitivity analysis indicated that the photosensitization process (contributed by ACE) was the dominant mechanism in the cocktail photolysis system, while the presence of a hydrogen source (TEA) did not contribute a major decay pathway but promoted the reaction rate of photosensitization by offering an add-on effect.