The Stability Enhancement of Covalent Organic Frameworks and Their Applications in Radionuclide Separation

Covalent organic frameworks ( COFs) are a class of crystalline organic porous polymers with long-range ordered structures prepared by reversible reactions. Due to high radiation resistance, structural designability and functionalization, COFs are expected to play a role in the efficient adsorption of radionuclides and the exploration of interaction mechanism. However, the reversibility of typical linkage bonds causes the limited chemical stability of COFs. This paper reviews the improvement strategies towards chemical stability of COFs (including the decrease of reversibility of linkage bonds, the post synthetic transformation from reversible bonds to irreversible ones, and the construction of hydrophobic environment around linkage bonds), crystalline control (including the influence of synthesis conditions, in layer coplanar and interlayer interaction for two-dimensional COFs and the crystallization of amorphous polymers), functionalization methods and the applications of COFs in the separation and enrichment of radionuclides. The interaction between radionuclides and COFs could be optimized by enhancing the strength of COFs skeleton, introducing special functional groups or changing the size of monomers. The application prospect and research focus of COFs in radionuclide separation are prospected.