Bicarbazolyl-based covalent organic frameworks for highly efficient capture of iodine and methyl iodide

Development of porous materials with excellent capture performance of radioactive iodides (mainly molecular I₂ and organic CH₃I) remains an ongoing challenge in nuclear industry. Currently, numerous efforts have been devoted to exploring novel adsorbents with good textural properties like high specific surface and large pore volume. However, some nonporous materials exhibited outstanding iodine adsorption capability. Therefore, it is not yet clear what factors determine the iodine uptake capacity. Herein, a novel paradigm of iodine capture that overturns previous cognition is proposed by exploring some 2D electron-donating nitrogen-containing covalent organic frameworks (COFs). As validated by different pores of 2D COFs shaping from rhombic to hexagonal and ranging from micropores to mesopores, their adsorption capabilities of either molecular I₂ or CH₃I are more likely to depend on the number of adsorption binding sites, rather than their textural properties. This novel paradigm of iodine capture is of great importance to design of porous materials for disposing of exhaust gases from nuclear power plants.

Graphical Abstract

For two-dimensional covalent organic frameworks that have same topological structure and electron-donating nitrogen-containing fragments with similar adsorption affinity to iodine molecules, their adsorption capabilities, for either molecular I₂ or organic CH₃I, are more likely to depend on the number of adsorption binding sites, rather than their textural properties like specific surface areas and pore volumes.