Incorporating Crown Ether Into Zirconium Metal-Organic Framework for Highly Selective Lithium-Ion Adsorption

Abstract

The rapid development of the lithium battery industry has significantly increased the demand for lithium resources. While abundant lithium exists in salt-lake brines, its efficient extraction remains challenging, highlighting the need for highly selective adsorbents. Herein, a stable zirconium-based metal-organic framework (Zr-MOF) was utilized as a platform to construct an adsorbent for Li⁺ by incorporating 4′-carboxybenzo-12-crown-4 (CE) onto [Zr₆O₈] cluster via ligand exchange. Zr-MOF not only provides abundant anchor sites for CE molecules but also creates efficient mass transport channels. The resulting CE@Zr-MOF exhibits excellent Li⁺ adsorption capacity, reaching up to 33.6 mg g⁻¹, and maintains high selectivity even in the presence of elevated concentrations of competing ions. Mechanistic studies reveal that the well-defined cavities of CE offer ideal binding sites for Li⁺, while steric hindrance reduces the affinity for interfering ions, thus enhancing selectivity. Moreover, Zr-MOF not only serves as a carrier but also enhances the adsorption capacity of CE through charge interactions. This work provides a rational design strategy for developing high-performance MOF-based adsorbents for lithium extraction.