[Adsorption of Acid Red 3R on chitosan and its enhancement by Cu2+ co-sorption]

Chitosan was used for the removal of Acid Red 3R from aqueous solutions. Batch adsorption studies were carried out to investigate adsorption kinetics and thermodynamics and the effect of coexisting pH, NaCl, and Cu2+ on adsorption. Experimental data were exploited for kinetic and thermodynamic evaluations related to the adsorption processes. The kinetic data correlated well with the pseudo-second-order kinetic model, indicating the chemical sorption via complex formation/ion exchange. The equilibrium data were well fitted by three isotherm models, namely, Langmuir, Freundlich and Dubinin-Radushkevich (D-R) equations. Moreover, adsorption of Acid Red 3R onto the chitosan was found to be strongly depending on solution temperature and pH. However, the addition of sodium chloride was found to have little effect on the adsorption process. Thermodynamic studies revealed the adsorption process was exothermic in natural. The adsorption free energies derived from D-R equation were in range of 9.5-10.7 kJ x mol(-1), implying that the sorption process is a chemical ion-exchange mechanism. In addition, adsorption capacity of chitosan to Acid Red 3R was found to be greatly enhanced in the presence of Cu2+. A model correlating the concentration of Cu2+ with the enhanced amount of dye adsorbed was established.