Synthesis of thiophene Schiff base functionalized UiO-66 for enhanced Cu (II) ion adsorption capacity and selectivity

Two UiO-66-supported thiophene Schiff base materials, UiO-66-TP and UiO-66-TPMe, were prepared for adsorbing Cu(II) ions from water. Both adsorbents exhibited improved Cu(II) adsorption performance compared to the precursor UiO-66-NH2. Experimental data confirmed that adsorption occurred via chemisorption on a monolayer, aligning with the pseudo-second-order kinetic and Langmuir isotherm models. In comparison to UiO66-TP which lacked a substituted group, UiO-66-TPMe exhibited a higher theoretical maximum adsorption capacity of 151.5 mg/g at pH 6.0. Thermodynamic experiments have shown that the uptake of Cu(II) was both endothermic and spontaneous in nature, leading to an increased disorder at the solid-solution interface. Moreover, in the presence of interfering metal ions, these two functionalized materials, based on thiophene Schiff base, demonstrated superior adsorption selectivity for Cu(II) compared to UiO-66-NH2. X-ray photoelectron spectroscopy analysis unveiled the coordination of Cu(II) with N and S atoms on the ligand during the adsorption process. Density functional theory calculations further supported a methyl substitution group on the thiophene Schiff base facilitated the binding of Cu(II) ions and a charge transfer occurred from the thiophene Schiff base ligands to Cu(II) ions upon complex formation.