Equilibrium, kinetic and thermodynamic studies of Reactive Red 120 dye adsorption by chitosan beads from aqueous solution

Chitosan beads (CHB) were prepared and studied in a batch mode operation for the adsorption of Reactive Red 120 dye from aqueous solution. Characterization on the surface of CHB was achieved by using point of zero charge (pH(pzc)) method, Fourier transform infrared spectroscopy, and scanning electron microscopy. Adsorbent dosage (0.02-1.5 g), initial pH solution (4-12), initial dye concentrations (30-400 mg/L), and contact time (2-500 min) were used as the function to optimize the adsorption equilibrium experiments that were carried out during the course of this study. The adsorption equilibrium data show that the adsorption process obeys the Langmuir model with maximum adsorption capacities of 114.9, 123.5 and 129.9 mg/g for 303, 313 and 323 K, respectively. The kinetics of the RR 120 adsorption was well-fitted to the pseudo-second-order kinetics. Thermodynamic parameters such as standard Gibbs free energy ( increment G degrees), standard enthalpy ( increment H degrees) and standard entropy ( increment S degrees) were determined. The positive value of enthalpy indicates that the uptake of RR 120 onto CHB is endothermic in nature. The results obtained supported the use of CHB as an effective as well as favorable adsorbent in treating RR 120 dye.