Pyridine-based ionic sp2 carbon-conjugated covalent organic frameworks for selective extraction of Pu(IV) from high-level liquid waste

In the current era marked by energy shortages, the advancement of nuclear energy stands as an inevitable progression. The reprocessing of spent nuclear fuel plays a crucial role in determining the sustainability of nuclear energy as a viable energy source. Among these processes, the separation and recovery of Pu(IV) from high-level liquid waste (HLLW) hold paramount significance in terms of safety and strategic implications. Herein, this work focused on the synthesis of two acid- and radiation-resistant pyridine-based sp²c-COFs (COF-IHEP3 and COF-IHEP4), followed by the creation of two pyridine-based ionized sp²c-COFs named COF-IHEP3-CH₃NO₃ and COF-IHEP4-CH₃NO₃ through post-modification. These materials have potential anion exchange capacity for the selective separation of Pu(IV) in highly acidic conditions. Notably, in 8 mol/L nitric acid solution, COF-IHEP3-CH₃NO₃ demonstrated the capability to eliminate plutonium within 20 min in 98% removal efficiency with a K_d value of 2450 mL/g. Experimental and theoretical analysis suggest that the ionized sp²c-COFs exhibit exceptional stability, selectivity, and prevention of secondary contamination towards Pu(IV) in the presence of multiple ions environments. In short, this work provides an appropriate anion exchange strategy to design ionic sp²c-COFs as a promising platform for Pu(IV) recovery from HLLW.