Crown ether-engineered core–shell magnetic microspheres for lithium ion-specific recognition and rapid magnetic separation

Abstract

The increasing demand for lithium in energy storage systems and electronic devices has highlighted the critical need for efficient and selective separation strategies, particularly from salt-lake brines and pre-concentrated lithium-rich streams, which contain high concentrations of competing cations such as Mg²⁺, Ca²⁺, Na⁺, and K⁺. In this study, a core–shell structured magnetic poslymer adsorbent functionalized with crown ether moieties (MNPs@PS@(PVBC-g-PGMA)-2M12C4) was systematically engineered for the selective recognition and recovery of Li⁺ ions. The adsorbent was synthesized by grafting 2-hydroxymethyl-12-crown-4 ether (2M12C4) onto a PGMA-modified magnetic polystyrene substrate via surface-initiated radical polymerization. The resulting adsorbent exhibited a rough spherical morphology with an average diameter of 260 nm, excellent surface functionality, and rapid magnetic responsiveness. Batch adsorption experiments revealed a maximum Li⁺ adsorption capacity of 10.62 mg g⁻¹, with equilibrium reached within 120 min. Kinetic and isotherm analyses indicated that monolayer chemisorption was governed by host–guest interactions between Li⁺ and the crown ether cavities. Notably, the adsorbent exhibited high selectivity for Li⁺ over coexisting cations, with selective separation coefficients (α₁) exceeding 6.0, and demonstrated excellent recyclability, retaining 96.83% of its initial adsorption capacity after eight consecutive cycles. These results underscore the potential of the crown ether-grafted magnetic polymer microspheres as robust and reusable platforms for lithium recovery from complex aqueous environments.