Guanidinium-based ionic covalent organic frameworks for capture of uranyl tricarbonate

Uranium, which was abundant in the ocean but existed in the form of uranyl tricarbonate ([UO 2 (CO 3 ) 3 ] 4− ) with an extremely low concentration of 3.3 ppb, was a significant element of nuclear energy. It is of immediate significance to the research into uranium extraction by the exploration of adsorbents for environment and resource sustainability. Herein, the new ionic covalent organic frameworks (iCOFs) named COF-DG containing the guanidine groups was designed and synthesized via Schiff base reaction between diaminoguanidine hydrochloride and 1,3,5-triformylphloroglucinol. The adsorption performance indicated that the COF-DG possessed an uptake capacity of 65.6 mg g −1 toward the [UO 2 (CO 3 ) 3 ] 4− , attributed to the chemical interaction and anion exchange between [UO 2 (CO 3 ) 3 ] 4− and the cationic COF-DG with Cl − , as well as the electrostatic attraction. Besides, the COF-DG exhibited a higher affinity and selectivity toward [UO 2 (CO 3 ) 3 ] 4− in the presence of the competing anions. Furthermore, the COF-DG displayed an antibacterial rate of 82% against Gram-negative bacteria Escherichia coli owing to the guanidine groups. This work contributes new insights into the further development of iCOFs, for applying as a potential candidate in uranium extraction from seawater in practical engineering. Graphical abstract The new ionic covalent organic frameworks named COF-DG was designed and exploited via Schiff base reaction, which exhibited a higher affinity and selectivity toward the [UO 2 (CO 3 ) 3 ] 4− .