Equilibrium Isotherms, Thermodynamics, and Kinetic Studies for the Adsorption of Food Azo Dyes onto Chitosan Films

The adsorption of FD&C red 2 and FD&C yellow 5 onto chitosan films (CFs) was evaluated by equilibrium isotherms, thermodynamics, and kinetic studies. The effects of temperature (298-328 K), initial dye concentration (50-300 mg L-1), stirring rate (50-350 rpm), and contact time (0-120 min) were investigated at pH of 2.0 and 100 mg L-1 of CFs. The dye concentration was determined by spectrophotometry. Freundlich and Langmuir models were used to represent the equilibrium data. The Langmuir model was the more adequate to represent the equilibrium data (R-2 > 0.99 and average relative error < 2.50%) and the maximum adsorption capacities were 494.13 and 480.00 mg g(-1) for FD&C red 2 and FD&C yellow 5, respectively, obtained at 298 K. The R-L values ranged from 0.044 to 0.145. The adsorption was exothermic, spontaneous, and favorable. For the FD&C red 2, 90% of saturation was attained at 120 min and the Elovich model was the more appropriate. For the FD&C yellow 5, 95% of saturation was attained at 20 min and the pseudo first-order model was the more adequate to fit the kinetic data. CFs were easily separated from the liquid phase after the adsorption process, providing benefits for industrial applications, and its application range can be extended for azo dyes.