Effective separation and immobilization of uranium(VI) from wastewater using amino and carboxyl groups functionalized covalent organic frameworks

Uranium pollution was a key problem affecting the sustainable development of nuclear energy. Herein, a novel covalent organic frameworks (TzDva) was constructed by the irreversible imidization reaction between 2, 4, 6-tris(4-aminophenyl)-1, 3, 5-triazine (Tz) and 2, 5-divinylterephthalal-dehyde (Dva), which were further functionalized by dimercaptosuccinic acid (DMSA) and 2-aminoethanethiol (AET) for efficient elimination of uranium(VI) from wastewater. Different spectral techniques were used to characterize the microscopic morphology and structure of all the adsorbents. The experimental results showed that the carboxyl functional groups exhibited a strong affinity for uranium(VI) than that of the amino functional groups, and the maximum extraction capacities of TzDva-COOH and TzDva-NH2 were 139.5 and 88.3 mg.g(-1), respectively. Selectivity experiments and simulated high salinity systems displayed that the two COFs had not only strong affinity for U (VI), but also powerful salt resistance. Meanwhile, the two COFs materials also exhibited good stability and high reusability after three adsorption-desorption cycles. Besides, spectroscopic analyses and DFT calculation demonstrated that the main adsorption mechanism involved electrostatic interactions, chelation and surface complexation. Thus, this work served as a good guideline for fabricate a novel COFs based materials to treat uranium-containing wastewater.