Tunable carboxyl ionic organic single-crystals for the ultrafast capture of thorium and uranium

The exploitation and utilization of nuclear energy have generated substantial amounts of wastewater containing thorium (Th(IV)) and uranium (U(VI)), posing significant ecological and radiological hazards. The development of eco-friendly and high-performance adsorbents for the separation of radioactive contaminants from wastewater is critical for the protection of the aquatic environment. Herein, a class of tunable carboxyl ionic organic single-crystals (IOCs, named PTA-TPPEE, BTC-TPPEE, and PMA-TPPEE) was developed under mild conditions via a rationally designed ionic self-assembly strategy. The selective capture of radioactive ions in wastewater by IOCs is attributed to their unique structural features. Specifically, TPPEE as the cationic ligand provides a stable framework with cavities, while H2PTA, H3BTC, and H4PMA as the anionic ligands, with different carboxyl groups, form strong bonds with these ions. The synergistic interaction between these components enables efficient selective capture, achieved through the combined effects of carboxyl oxygen atom coordination at dense chelation sites and IOCs-radionuclide electrostatic interactions as dual selectivity drivers. Among the three IOCs synthesized, PTA-TPPEE, characterized by a larger specific surface area, demonstrated superior thorium and uranium adsorption performance. It effectively separates target ions under acidic conditions, achieving high saturation separation capacities (Th(IV) 582.0 mg g−1, U(VI) 325.7 mg g−1), ultrafast adsorption kinetics (Th(IV) 99.8%, U(VI) 99.5%) within 1 min, and excellent reusability over five cycles. The partition coefficients of PTA-TPPEE for Th(IV) and U(VI) are 102 to 103 times higher than some co-existing ions. As a verification test, the adsorption in rare earth mine wastewater and other water systems has confirmed that PTA-TPPEE can efficiently purify radioactive ions. These findings reveal the exceptional performance of IOCs in the separation of Th(IV) and U(VI), underscoring their promising prospects in wastewater treatment. Thus, it represents a promising candidate for their practical applications in the selective recovery of Th(IV) and U(VI).