Adsorption of La3+ onto trifluoroacetic acid modified UiO-66-COOH: Adsorption mechanism and application

The application of metal organic frameworks (MOFs) for the recovery of low concentrations of rare-earth elements (REEs) has attracted increasing attention due to the precious value of REEs resources. In this study, UiO66-COOH was modified by trifluoroacetic acid (TFA) to not only promote material crystallization and the pore structure verified by XRD and SEM characterization, but successfully enhance its adsorption capacity and achieve perfect selectivity for Lanthanum ion (La3+). The adsorption capacity for UiO-66-COOH-24TFA was increased by 58% compared to unmodified material. The adsorption mechanism and application were comprehensively investigated. By adsorption kinetics, isotherm and thermodynamic studies, it was found that the adsorption process mainly exhibited monolayer adsorption with spontaneous endothermic-chemisorption characteristics, and -COOH of the modified materials (UiO-66-COOH-24TFA) played an important role, which was confirmed by XPS. Moreover, UiO-66-COOH-24TFA was applied to REEs actual wastewater by successive six-stage adsorption process, where the overall recovery rate on La3+ reached 94.1% under the coexisting conditions of multiple ions.