Pyridinium salt-based covalent organic framework with well-defined nanochannels for efficient and selective capture of aqueous 99TcO4−.

A cationic pyridinium salt-based COF was synthesized and structurally characterized. PS-COF-1 showed the highest experimental BET surface area (2702.7 m2 g−1) reported to date for any cationic COF material. Endowed by unique structural features, PS-COF-1 showed outstanding performance for the selective adsorption of 99TcO 4 − (and ReO 4 −), suggesting great potential for 99TcO 4 − removal from nuclear wastes and in environmental remediation. [Display omitted] 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 m2 g−1, 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 4 − (1262 mg g−1) and 99TcO 4 −. Its adsorption performance surpassed its corresponding amorphous analogue. Importantly, PS-COF-1 exhibited fast adsorption kinetics, high adsorption capacities, and selectivity for 99TcO 4 − and ReO 4 − at high ionic strengths, leading to the successful removal of 99TcO 4 − under conditions relevant to low-activity waste streams at US legacy Hanford nuclear sites. In addition, PS-COF-1 can rapidly decontaminate ReO 4 −/99TcO 4 − 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 4 − and 99TcO 4 −, thereby favoring adsorption of these low charge density anions over other common anions (e.g., Cl−, NO 3 −, SO 4 2−, CO 3 2−). Our work demonstrates a novel cationic COF sorbent for selective radionuclide capture and legacy nuclear waste management. [ABSTRACT FROM AUTHOR]