A Nanoporous Ionic Covalent Organic Framework for Rapid and Selective Scavenging of Toxic Heavy Metal-Based Oxo-Anions and Iodine

Designing ionic porous material that combine high charge density, robust stability, and selective anion sequestration remains a significant challenge for environmental remediation. In this study, we present a guanidinium-based ionic covalent organic framework (iCOF-1) that was synthesized via a metal-free Schiff-base polycondensation reaction. The cationic nitrogen-rich framework of iCOF-1 contains exchangeable chloride counterions, enabling the rapid and selective capture of toxic heavy metal-based oxo-anions (CrO42−, Cr2O72−, and MnO4−) and iodine species (I2 and I3−). iCOF-1 exhibits exceptional adsorption capacities of 797.2 mg g−1 for MnO4−, 396.3 mg g−1 for CrO42−, 338.4 mg g−1 for Cr2O72−, and 1943 mg g−1 for I3−. Notably, iCOF-1 achieves distribution coefficients exceeding 106 mL g−1 and over 99% removal within minutes, even in the presence of competing anions, highlighting its rapid and selective anionic pollutant sequestration capability. iCOF-1 performs effectively in both column and syringe filtration and can be regenerated over multiple cycles without loss of performance. Spectroscopic techniques and DFT studies reveal a dual capture mechanism involving ion exchange and physisorption, which is governed by electrostatic and hydrogen-bonding interactions. This work establishes a molecular design strategy to obtain high-performance ionic COFs for water purification and nuclear waste management.