Dynamic polyiodide anions formation in cationic covalent organic framework for efficient iodine capture

Rapid and efficient capture of iodine is very important for the treatment of radioactive nuclear waste, but the traditional iodine adsorbents have the disadvantages, including the slow adsorption rate and the low adsorption capacity. To address these problems, herein, a new cationic vinyl-based covalent organic framework (COF) with abundant dissociative iodide anions was synthesized by Knoevenagel condensation and the post-ionization modification (PIM) reaction. The resulting ionic COF (iCOF-TMPT) has high specific surface area, excellent chemical stability, as well as the high-density pyridine cations and abundant dissociative iodide anions, which is beneficial for the highly efficient iodine adsorption. The iCOF-TMPT not only has the outstanding iodine adsorption capacity for iodine vapor and solution (6.61 g g−1 for iodine vapor and 1.55 g g−1 for iodine solution), but also possesses the remarkable iodine adsorption rate of 2.81 g h−1, which surpasses any other reported COF absorbents. The adsorption mechanism indicated that the dissociative iodide ions in iCOF-TMPT can induce neutral iodine molecules to generate polyiodide anions, and the pyridine cations in iCOF-TMPT can form strong Coulomb interaction with the formed polyiodide anions. This work not only provides a novel cationic vinyl-based two-dimensional COF with ultra-high chemical stability by Knoevenagel condensation and PIM reaction, the high-density pyridine cations and extra-framework iodide ions can achieve efficient I2 capture by inducing the formation of polyiodide.