Building block design of thermally regenerable metal–organic framework composites for highly selective lithium adsorption

Crown ether-based organic lithium adsorbent has good stability for diverse lithium extraction scenarios, but hindering by its relatively low selectivity. Here, we report a building block design strategy for fabricating highly selective and thermally regenerable 12-crown-4 (12CE4) based lithium adsorbent. The synergistic coordination and ion-sieving blocks can sufficiently improve the ion selectivity and adsorption capacity of pNCE@MOF fabricated by copolymerizing thermosensitive segment and 12CE4 inside MOF. With the aid of synergistic coordination component of sulfonate group (SS), its Li⁺/Mg²⁺ selectivity increased from 12.9 to 21.8 (pNCE-SS@UiO-66) tested in 10,000 ppm salt solutions. Moreover, the 6.0 Å window of UiO-66 could successfully sieve hydrated Li⁺ (7.64 Å) and Mg²⁺ (8.56 Å), enhancing the selectivity 3.3 times from 5.1 for pNCE-SS@MOF-808 (10.0 Å) to 21.8. The adsorption capacity of pNCE-SS@UiO-66 was also optimized from 1.00 to 1.47 mmol·g⁻¹. Furthermore, this material demonstrated a lithium selectivity of 11.5–19.8 in synthetic brines with a Mg/Li ratio of 1 to 0.1. Importantly, it could be fully regenerated in warm water at ≥ 40 °C. This work opens the door to constructing highly ion-selective functional materials via a modular method.