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

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 ΔadsH, ΔadsG and ΔadsS, were determined for all the factorial design results. Exothermic and endothermic values were found in relation to the ΔadsH. The positive ΔadsS values indicate that entropy is a driving force for adsorption. The ΔadsG values are significantly affected by an important synergistic effect of the factors and not by the temperature changes alone.