Degradation of Orange G dye by hexacyanoferrate(III) ions in the presence of Iridium nanoparticles: effect of system parameters and kinetic study

The kinetics of the catalytic degradation of Orange G (OG), an azo dye containing two sulphonic groups, by hexacyanoferrate(III) ions (HCF(III)) in the presence of iridium nanoparticles (Ir nano) has been investigated. The effect of various operational parameters such as the concentration of dye, oxidant, catalyst and solution pH on the reaction rate have been determined. The results show that the reaction follows first-order kinetics with respect to [HCF(III)] at optimum pH 8.0 and constant temperature of 40 +/- 0.1 degrees C. The order of reaction with respect to [OG] has been found to be one at its lower concentration tending towards zero at its higher concentration. The reaction rate increases with an increase in the concentration of iridium nanoparticles used as catalyst which reveals the good catalytic activity of Ir nano. Thermodynamic parameters have been calculated by studying the reaction rate at four different temperatures. Based on the experimental results, a plausible reaction mechanism involving complex formation and rate law has been derived. The UV-vis, FT-IR, HPLC, LC-MS of degradation product showed the formation of simpler and less hazardous compound, 6-hydroxyamino benzene-1,2-diethanoic acid, 6-hydroxyamino benzene-1,2-diethanoic anhydride and 7-hydroxy naphthalene-1,3-disulphonic acid as minor degradation products and pentanoic acid, propanoic acid, ethanoic acid as major degradation products.