Abstract
Owing to the growing industrial demand worldwide and limited mineral deposits, the recovery of low-concentration rare earth elements (REEs) from waste sources is being considered, which also helps to reduce water pollution. In this work, the adsorption of gadolinium ions (Gd3+) in aqueous solutions over a functionalized metal–organic framework (MOF), UiO-66, was investigated. Initially, the MOF structure was synthesized solvothermally using a ligand mixture of terephthalic and trimellitic acids to produce coordination-free −COOH groups on the UiO-66 framework. Subsequently, the −COOH group was reacted with ethylenediamine to introduce additional −NH2 groups onto the MOF. The optimized product (denoted as UiO-66-COOH-ED) showed an equilibrium adsorption capacity of 79 mg/g for Gd3+ compared with 16 mg/g by pristine UiO-66. This improvement in adsorption by a factor of 4.9 was a consequence of the coordination of Gd3+ ions with the electron-abundant oxygen and nitrogen atoms of −COOH and −NH2 groups. A solu...
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