Linear and nonlinear isotherm, kinetic and thermodynamic behavior of methyl orange adsorption using modulated Al₂O₃@UiO-66 via acetic acid

The kinetic, isotherm and thermodynamic parameters of adsorption were investigated to obtain the optimum conditions of adsorption. Error analysis methods such as RMSE and χ² were used to determine the best kinetic equation and isotherm. From the adsorption kinetics study, the linear pseudo second order model showed an effective adsorption mechanism and the most suitable adsorption isotherm was the linear Langmuir isotherm model. Based on the linear Langmuir isotherm model, the maximum adsorption capacities of UiO-66 and Al(M100)@UiO-66 were 233.65 and 268.82 mg/g, respectively. The results showed that the linear method was better suited to take into account the adsorption parameters than the nonlinear method. The resulting R² values of other kinetic models, namely Intraparticle Diffusion and Elovich, were still below that of the linear pseudo second order model and the resulting R² values of other isotherm models, namely Temkin, Dubinin-Radushkevich, and Scatchard, were still below that of the linear Langmuir isotherm model. The adsorption thermodynamic study showed that the adsorption process was exothermic and spontaneous. Other operational parameters such as pH, ionic strength and adsorbent dose were also discussed. Al(M100)@UiO-66 can be regenerated up to four times using a diluted HCI solution.