The removal of an anionic red dye from aqueous solutions using chitosan beads—The role of experimental factors on adsorption using a full factorial design

Abstract

A factorial design was employed to evaluate the quantitative removal of an anionic red dye from aqueous solutions on epichlorohydrin-cross-linked chitosan. The experimental factors and their respective levels studied were the initial dye concentration in solution (25 or 600 mg L −1), the absence or the presence of the anionic surfactant sodium dodecylbenzenesulfonate (DBS) and the adsorption temperature (25 or 55 °C). The adsorption parameters were analyzed statistically using modeling polynomial equations. The results indicated that increasing the dye concentration from 25 to 600 mg L −1 increases the dye adsorption whereas the presence of DBS increases it. The principal effect of temperature did not show a high statistical significance. The factorial results also demonstrate the existence of statistically significant binary interactions of the experimental factors. The adsorption thermodynamic parameters, namely Δ ads H, Δ ads G and Δ ads S, were determined for all the factorial design results. Exothermic and endothermic values were found in relation to the Δ ads H. The positive Δ ads S values indicate that entropy is a driving force for adsorption. The Δ ads G values are significantly affected by an important synergistic effect of the factors and not by the temperature changes alone.