Kinetics and optimization of photolytic decoloration of carmine by UV/H₂O₂

Carmine (C.I. name is Natural Red 4), a naturally occurring important dye, was subjected to UV radiation in the presence of hydrogen peroxide. The photo-oxidation of the dye was monitored spectrophotometrically. The apparent rate of decoloration was calculated from the observed absorption data and was found to be of first order. A systematic study of the effect of dye concentration as well as H₂O₂ concentration on the kinetics of dye decoloration was carried out. Additionally, the effect of various additives on the decoloration of this dye was also investigated. Most of the anions tested had an inhibitory effect on the decoloration of the dye, with the most pronounced effect seen with sulfite ion as compared to carbonate, sulphate, nitrate and chloride ions. Examination of the effect of pH showed that the dye could be efficiently decolorized in a basic media. A plausible explanation involving the probable radical initiated mechanism was given to explain the dye decoloration. Lastly, we used HPLC analysis to show that the decoloration of carmine observed during the UV/H₂O₂ photolysis treatment was in fact due to the degradation of the dye.