Rational Designed Metal–Organic Framework with Nanocavity Traps for Selectively Recognizing and Separating of Radioactive Thorium in Rare Earth Wastewater

Facing the complex coexistence of various metal ions in wastewater and mineral resources, metal–organic frameworks (MOFs) with diverse functionalities and tunable pores are poised to serve as distinctive solutions for efficiently recognizing and selectively separating radioactive thorium (Th(IV)). Herein, a fluorescent MOF (DBT‐DHTA‐Cd) with unique thorium nanocavity traps is rationally designed by using two rigid ligands, including azole and hydroxyl groups, respectively. Notably, the synergistic effect of the appropriate pore size and dense hydroxyl···N nanocavity traps in DBT‐DHTA‐Cd results in selective capture of Th(IV), arising from the high charge density of nano‐trap and extremely low binding energy (Eads = −602.7 KJ mol−1). The fast adsorption kinetics (30 min) and rapid fluorescence response (1 min) of DBT‐DHTA‐Cd toward Th(IV) are attributed to the stronger electron holding capacity of the d and f orbitals belonged to Th(IV), making it more prone to accepting electrons transferred from the N/O active sites in the nano‐trap. As a verification test, tailing breakthrough experiments confirm that DBT‐DHTA‐Cd can efficiently purify Th(IV) from monazite mining solid waste in one step. This work provides profound insights into relationship between structure and property of MOFs and has valuable guidance for designing materials in the radioactive purification field. A novel fluorescent MOF (DBT‐DHTA‐Cd) featuring with azole and hydroxyl groups has been synthesized using a dual‐ligand strategy, which efficiently recognizes and separates Th(IV) through the synergistic effects of tailored pore size and densely hydroxyl···N nanocavities. It demonstrates rapid kinetics for Th(IV) and achieves efficient single‐step purification of Th(IV) from monazite mining waste.