One-dimensional fluorescent covalent organic frameworks rich in exposed sp3-N sites for ultra-fast iodine capture and visual monitoring

Abstract

It is important to capture radioactive iodine, especially highly volatile CH₃I and I₂, from nuclear waste for pollution control. Research has indicated the great potential that covalent organic frameworks possess for iodine capture, and several covalent organic frameworks (COFs) with high adsorption capacities have been reported. However, increasing the capture rate of gaseous iodine remains a major challenge at present. To this end, researchers have improved iodine capture rates by introducing macropores, nitrogen sites, and heteroatoms. In the field of catalysis, 1D COFs have been used due to their abundant exposed sites. Inspired by this, we postulated that it is feasible to increase the exposure of N sites to increase the iodine capture rate. Herein, we report a strategy based on 1D COFs (COF-1D6 and COF-1D7) with the introduction of exposed sites, which significantly enhances the adsorption rates of I₂ and CH₃I, while maintaining a high loading capacity. In particular, COF-1D6 with completely exposed sites exhibited a K_80% of 1.07 g g⁻¹ h⁻¹, which is far higher than that of other reported COF adsorbents. The excellent fluorescence of COF-1D6 also enabled visual monitoring of the CH₃I adsorption process. This work provides new insights into rapid iodine capture from the perspective of exposure sites.