Imaging Solvent-Triggered Gaseous Iodine Uptake on Single Covalent Organic Frameworks

Covalent organic frameworks (COFs) are promising solid absorbents for the treatment of gaseous iodine. However, extensive efforts are still focused on empirical optimizations of specific binding sites and pore structures in COFs, and the chemical control of gaseous iodine uptake on COFs remains challenging. In this study, the chemically triggered sorption properties of COF-300 for I-2 vapors at the single-particle level with the dark-field microscope (DFM) are explored. The present operando single-particle DFM imaging method enables the direct visualization of an adsorption activity transformation from inactive COF-300 to active solvated COF-300 toward gaseous I-2 vapors. Exploiting the useful reaction information from time-lapsed DFM images, the tunable adsorption performance of solvated COF-300 is quantitatively compared by various solvents. The results illustrate that the isopropanol (IPA)-solvated COF-300 achieves the optimum adsorption capacity for I-2 among the absorbents. The reaction mechanism is elucidated to be the channel size enlargement and modification of internal surface chemistry in the IPA-solvated COF-300, producing a stable I-2/IPA-solvated COF-300 complex after the sorption reaction. The present chemical control of the sorption behavior of COF-300 revealed by DFM opens up a new fundamental paradigm for rationally developing high-performance COF-based absorbents for removing I-2 vapors.