Kinetic and Equilibrium Studies on Adsorptive Removal of Toluidine Blue by Water-Insoluble Starch Sulfate

The aim of this research was to estimate the adsorption performance of water-insoluble starch sulfate (SS) for cationic dyes. Toluidine blue (TB), as a model cationic dye, was used to prepare an adsorbate solution. The effects of adsorption time, initial TB concentration, temperature, and initial pH on the adsorption of TB by SS were studied, and the kinetics and equilibrium of the adsorption process were investigated using a nonlinear analysis method. The results showed that SS can effectively remove TB from the aqueous solution. The adsorption kinetic data correlate well with the pseudofirst-order kinetic model. The Langmuir, Freundlich, Toth, and Sips isotherm models were applied in the adsorption equilibrium study. The Toth isotherms had the best applicability to describe the TB adsorption and show that the adsorption energies follow a heterogeneous distribution. The maximum adsorption capacity from the Toth isotherm fitting is 26.56 mg . g(-1) The results of thermodynamics studies show that the adsorption process of TB on SS is exothermic in nature. The adsorption of TB on SS is highly pH-dependent, and the optimal adsorption effect is achieved at pH = 6.0.