The Effect of Mordant on Carmine Adsorption Thermodynamics and Kinetics

The effect of mordant on the adsorption kinetics and thermodynamics of carmine dye were studied by analyzing the dyeing process at 25, 55, 75 and 85^oC at a constant initial dye concentration by measuring the absorbance using UV- visible adsorption spectroscopy at λ_max 500 nm. The adsorption kinetics were found to follow a pseudo first-order kinetic model for all the mordants tested, as a high correlation coefficient (R²) was obtained for the first-order model and the activation energies obtained for all the mordants ranged between 10.4-13.3 kJ/mol. It was also determined that the presence of mordant had a statistically significant effect on the rate constant. Langmuir and Freundlich adsorption isotherms were applied to describe the experimental equilibrium isotherms. The results indicate that Freundlich model provides the best correlation. Thermodynamic parameters: free energy (∆G^o), enthalpy (∆H^o) and entropy (∆S^o) were also determined for carmine dyeing. The thermodynamic parameters showed that for all mordants, adsorption is spontaneous and thermodynamically favorable. It was deduced that the dyeing process is likely to be controlled by a physisorption process for both adsorption and kinetic studies.