Olefin-linked cationic covalent organic frameworks for efficient extraction of ReO4−/99TcO4−

Efficient extraction of radioactive 99TcO4- from strong acid/base solutions by porous adsorbents is extremely desirable but remains a great challenge. To overcome the challenge, here we report the first example of an olefin-linked cationic covalent organic framework (COF) named BDBI-TMT with excellent acid, base and radiation stability is synthesized by integrating robust imidazolium salt-based linkers with triazine building blocks. BDBI-TMT shows an ultra-fast adsorption kinetics (equilibrium is reached within 1 min) and an excellent ReO4- (a non-radioactive surrogate of 99TcO4-) capture capacity of 726 mg g-1, which can be attributed to the abundance of precisely tailored imidazolium salt-based units on the highly accessible pore walls of the ordered pore channels. Furthermore, the formation of the highly conjugated bulky alkyl skeleton enhances the hydrophobicity of BDBI-TMT, which significantly improves not only the affinity toward ReO4-/99TcO4- but also the chemical stability, allowing selective and reversible extraction of ReO4-/99TcO4- even under extreme conditions. This work demonstrates the great potential of olefin-linked cationic COFs for ReO4-/99TcO4- extraction, providing a new avenue to construct high-performance porous adsorbents for radionuclide remediation.