Chelating effect between uranyl and pyridine N containing covalent organic frameworks: A combined experimental and DFT approach

Covalent organic frameworks (COFs) are promising adsorbents for removing heavy metal ions , and have high crystallinity , a porous structure, and conjugated stability. N -containing functional groups are known to have great affinity for uranyl ions. In this work, to explore the peculiarity of the pyridine N structure as an efficient adsorbent, we chose 2,2′-dipyridine-5,5′-diamine (Bpy) and pyridine-2,5′-diamine (Py) as the core skeletons, and 1,3,5-triformylphloroglucinol (Tp) as the linker to synthesize two crystalline and stable N -containing COFs named TpBpy and TpPy, respectively, through a facile solvothermal method . Characterization results demonstrated that TpBpy and TpPy possessed regularly growing pore sizes, large specific surface areas and relatively strong thermal resistances . The results of batch experiments showed that both COF materials were capable of the effective removal of uranyl with uptake capacities of 115.45 mg g −1 and 291.79 mg g −1 , respectively. In addition, density functional theory (DFT) simulations highlighted the beneficial chelation effect of the double N structure in pyridine monomers for removing uranyl ions. Combining systematic experimental and theoretical analyses, the adsorption process and interaction mode of porous COFs and UO 2 2+ were revealed, to provide predictable support for the application of pyridine N -containing COFs in the field of environmental remediation.