Pyridinium salt-based covalent organic framework with well-defined nanochannels for efficient and selective capture of aqueous TcO.

Ionic covalent organic framework (COF) materials with high specific surface areas and well-defined pore structures are desired for many applications yet seldom reported. Herein, we report a cationic pyridinium salt-based COF (PS-COF-1) with a Brunauer-Emmett-Teller (BET) surface area of 2703 m g, state-of-the-art for an ionic COF. Aided by its ordered pore structure, chemical stability, and radiation resistance, PS-COF-1 showed exceptional adsorption properties toward aqueous ReO (1262 mg g) and TcO. Its adsorption performance surpassed its corresponding amorphous analogue. Importantly, PS-COF-1 exhibited fast adsorption kinetics, high adsorption capacities, and selectivity for TcO and ReO at high ionic strengths, leading to the successful removal of TcO under conditions relevant to low-activity waste streams at US legacy Hanford nuclear sites. In addition, PS-COF-1 can rapidly decontaminate ReO/TcO polluted potable water (∼10 ppb) to drinking water level (0 ppb, part per billion) within 10 min. Density functional theory (DFT) calculations revealed PS-COF-1 has a strong affinity for ReO and TcO, thereby favoring adsorption of these low charge density anions over other common anions (e.g., Cl, NO, SO, CO). Our work demonstrates a novel cationic COF sorbent for selective radionuclide capture and legacy nuclear waste management.