Insight into volatile iodine uptake properties of covalent organic frameworks with different conjugated structures

The effective capture and storage of volatile radionuclide iodine from the nuclear waste stream is of great significance for environment remediation. Here we synthetize two types of two-dimensional (2D) covalent organic frameworks (COFs) for iodine vapor uptake, including COF-LZU1 with a whole pi-pi conjugated structure and TpPa-1 with a combination of pi-pi and p-pi conjugated structure. The capacities for iodine vapor uptake are acquired for COF-LZU1 (530 wt%) and TpPa-1 (245 wt%). Thorough studies reveal that the large and intact pi-pi conjugated system formed by phenyl rings and imine (-C=N-) linkers in COF-LZU1 provides materials with ultrahigh iodine vapor uptake by inducing the charge-transfer interactions to transform adsorbed iodine molecules into polyiodide anions. However, the combined ic-conjugated structure in TpPa-1 shows no obvious effect on iodine adsorption enhancement. Hence, this study can provide a guidance for the design and construction of ultrahigh-capacity iodine adsorbents.