Removal of toluidine blue from aqueous solution using orange peel waste (OPW)

The adsorption of toluidine blue, a basic dye, onto orange peel waste (OPW) was investigated using a batch adsorption technique. A series of assays were undertaken to assess the effect of the system variables, i.e. initial dye concentration, amount of adsorbent, pH, ionic strength, and solution temperature. The experimental data were analyzed by Langmuir, Freundlich, and Temkin isotherm models. Equilibrium data fitted well with the Langmuir model with maximum monolayer adsorption capacity of 314.3 mg g−1. Besides, the experimental results showed that the pseudo-second-order equation is the best model that describes the adsorption behavior and rate constants were estimated. Thermodynamic parameters were evaluated and the negative value of ΔH indicated exothermic nature of adsorption. This work demonstrates that OPW is suitable as an adsorbent material for adsorption from aqueous solutions.