Adsorptive Removal of 4-Chloro-2-Methylphenoxyacetic Acid from Aqueous Solution Using Uio-66(Zr)-Impregnated Amino Acid Ionic Liquid: Experimental and Molecular Docking Simulation

Abstract

Metal-organic framework UiO-66(Zr)-impregnated with 5.0 wt.% of cholinium alanate ([Ch][Ala]) was synthesized via solvothermal method to investigate their potential for adsorbing 4-chloro-2-methylphenoxyacetic acid (MCPA). The hybrid MOF was characterized by XRD, FESEM, N2 adsorption-desorption isotherms, FTIR, and TGA. The impregnation of ionic liquid inside the pores of UiO-66(Zr) and their interaction with the MOF’s cavities were confirmed by FTIR, TGA, and molecular docking. Adding [Ch][Ala] content reduced the surface area due to pore blockage by the ions. The removal efficiency of MCPA was evaluated using central composite design (CCD) of response surface methodology (RSM). The optimal MCPA removal percentages were 94.22% and 97.62% for pristine UiO-66(Zr) and UiO-66(Zr)/[Ch][Ala]@5%, respectively. The optimal conditions for the adsorption process were observed at 40°C, a contact time of 35 minutes, an adsorbent dosage of 40 mg, and an initial MCPA concentration of 40 mg/L, except for UiO-66(Zr)/[Ch][Ala]@5%, where the optimum temperature was 30°C and the initial concentration was 20 mg/L. Adsorption isotherms were best described by the Freundlich model, indicating multilayer adsorption on heterogeneous surfaces, as indicated by the lowest surface heterogeneity value of 0.4152 for the hybrid MOF composite. The thermodynamic analysis revealed that the adsorption process was both exothermic and spontaneous. Moreover, docking simulations showed the presence of π-π, anion-π and hydrogen bonding interactions, which contributed to the stronger interaction between MCPA and the UiO-66(Zr)/[Ch][Ala]@5%, in agreement with experimental findings.

Keywords: Metal-Organic Framework, UiO-66(Zr), response surface methodology, 4-chloro-2-methylphenoxyacetic acid (MCPA), adsorption isotherm, docking.