Modeling of the adsorption of acidic dyes by chitosan using both kinetic and thermodynamic comparisons

Two chitosans from two different sources crab shell chitosan (CC) and deep-pink shrimp chitosan (CP) were used in a batch system to test the adsorption of two acidic dyes, Acid Red 183 (AR183) and Acid Red 114 (AR114), and the results were compared with those of acid-washed powdered activated carbon (PAC). The effects of temperature, contact time, and starting dye concentration on the removal of AR114 and AR183 dye were investigated in a series of batch adsorption studies. The two chitosans had the highest dye absorption capacity for each AR dye-adsorbent system at 45 degrees C. The capacity of each adsorbent to adsorb increased when the initial dye concentration was increased up to 500 mg L-1. Chitosan CP was the most efficient of the three adsorbents, with maximum AR114 and AR183 absorption of 440 and 447 mg g-1, respectively, at 45 degrees C. At all concentrations and temperatures examined, the pseudo-second-order kinetic model accurately represented the adsorption kinetics, and the rate constants of second-order adsorption (k2) at these temperatures were calculated, respectively. The thermodynamic study revealed that the adsorption of dyes on chitosans was feasible, spontaneous, and endothermic process, and the adsorption of the dyes on each adsorbent may be chemical in nature. Results indicated that the synthesized chitosans were shown to be a promising adsorbent for the removal of dyes from aqueous solutions.