Kinetic analysis of azo dye decolorization during their acid-base equilibria: photocatalytic degradation of tartrazine and sunset yellow

In this study, the kinetics of the photodegradation of tartrazine (TA) and sunset yellow (SY) was systematically evaluated at different pH values in the presence of alpha-Fe2O3 nanostructures as a cost-effective and efficient photocatalyst. For each dye, time-spectral data was recorded in the pH range 8-12, then the whole data was resolved by hard soft-modelling parallel factor analysis to obtain the kinetic profiles of the components existing during simultaneous kinetic and equilibria processes. Then, the rate constants of degradation processes together with their uncertainties were computed. The results revealed that pH strongly affects the mechanism and the rate constants of the dyes photoreactivity due to changing the structure of the analytes. In fact, those protonated/deprotonated structures with resonance forms were less degradable because of their stability and then showed lower rate constant(s).