A comprehensive feasibility study on adsorption of Cu(II) and a water-soluble nitrazine yellow (NY) dye by chitosan-montmorillonite (CS-MMT) hydrogel as the biosorbent was investigated as a function of biosorbent dosage, initial concentration, pH, temperature, and the presence of salts. Box-Behnken methodology was applied to optimize the adsorption experiments. Maximum adsorption values were determined as 132.74 mg/g and 144.41 mg/g at pH=5.0, for Cu(II) and NY dye, respectively. Equilibrium isotherms of Langmuir and Freundlich were analyzed by the non-linear regression model. The equilibrium data were well described by Freundlich model and the adsorption process well fitted pseudo-second order kinetics. The enthalpy change of adsorption (H degrees) were calculated as -3.78 kJ/mol and -5.75 kJ/mol for Cu(II) and NY dye, respectively, indicating that the adsorption processes were exothermic. (c) 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 43664.