Amino acid-driven interface modulation in MOFs for sustainable lithium ion separation in complex aqueous media

The growing demand for lithium (Li⁺) and the accumulation of spent lithium-ion batteries necessitate efficient and selective separation strategies from complex aqueous systems. Herein, we report an amino acid–driven interface modulation approach for UiO-66-NH₂ via post-synthetic grafting of glutamic acid (Glu) and lysine (Lys). This strategy aims to enhance framework stability, Li⁺ selectivity, and pH adaptability. Structural and spectroscopic characterizations (PXRD, TGA-DSC, FTIR, XPS, SEM) confirm the successful incorporation of functional groups without compromising MOF crystallinity. The modified materials of Glu-UiO-66-NH₂ and Lys-UiO-66-NH₂ exhibits significantly improved Li⁺ adsorption capacities (up to 48 mg g⁻¹), excellent pH tolerance (5–11), and high selectivity over Co²⁺, Ni²⁺, and Mn²⁺ in competitive systems. Lys-UiO-66-NH₂, in particular, facilitates multidentate coordination via both amino and carboxyl groups, enabling enhanced Li⁺ binding affinity. Kinetic and isotherm analyses indicate monolayer adsorption at uniformly distributed active sites, dominated by N- and O-based ligand interactions. Thermodynamic results further confirm an endothermic and spontaneous chemisorption process, with amino acid grafting, especially glutamic acid, enhancing the interactions between Li⁺ and the material surface. These findings highlight the effectiveness of amino acid-driven interface modulation in MOFs for designing robust and selective adsorbents with promising potential for Li⁺ separation in aqueous media.