Experimental and computational insights into the iodine vapor capture by imine-and amine-linked covalent organic frameworks

Iodine capture from gas phase has gained enormous environmental importance due to the harmful effects of iodine pollution on human and other living organisms. In the current paper, an amine-linked covalent organic framework (AL-COF) is prepared by the partial in-situ reduction of the imine-linked COF (IL-COF) under the Eschweiler-Clarke conditions. The flexibility of the AL-COF and its synergic effect with the stronger hydrogenbond donor ability of amine -HC-NH- compared to the imine -C--N- linkages, led to a significant increase in the iodine adsorption capacity of the COF from 2.7 g.g- 1 for the IL-COF to 5.0 g.g- 1 for the AL-COF at 85 degrees C and atmospheric pressure. The specific surface area, and pore volume of the IL-COF were altered respectively from 70 m2.g-1 and 0.0642 cm3.g-1 to 58 m2.g-1 and 0.0811 cm3.g-1 for AL-COF. The iodine adsorption type was investigated using the FT-IR, XPS, Raman and DRS analyses. The adsorption of iodine on these two relative COFs is studied deeply with density-functional theory (DFT) computations employing B3LYP/LANL2DZ method. The UV-Vis absorption spectra obtained by TD-DFT method include charge transfer transitions between the iodine species (I-, I2, and I-3 ) and the designed IL-COF and AL-COF models. Also, various possible COF-iodine structures of the adsorption complexes were optimized and investigated based on the charge distribution and reduced density gradient (RDG). The computational and experimental results show compatible trends for the observed adsorption of iodine over these COFs surfaces.