Two-dimensional hydrazone-linked covalent organic frameworks for iodine capture

With the rapid expansion and development of nuclear energy, the safe disposal of radioactive materials, especially iodine-containing nuclear waste, has become a serious concern. It is thus of significance to design adsorbent materials that can efficiently remove iodine and clarify the interaction between iodine and the material surface. In this work, three two-dimensional (2D) hydrazone-linked covalent organic frameworks (COFs), i. e., DETH-TB-COF, DETH-TFPB-COF and DETH-TATBA-COF, were synthesized via a Schiff-base condensation reaction, based on a nitrogen-rich linear building unit, 2,5-diethoxybenzene-1,4-dicarbohydrazide (DETH). Owing to high crystallinity, large porosity, excellent chemical stability, and good binding affinities towards iodine, the resultant COFs show a good iodine adsorption capacity for volatile iodine. At 75 degrees C under ambient pressure, the iodine adsorption capacities of the three COFs reached 2.53, 3.89, and 4.23 g g-1, respectively. Their good adsorption capability can be maintained even after five cycles. Furthermore, the mechanism analysis indicates the formation of electron transfer complexes between iodine molecules and the material surface, thereby enhancing the iodine adsorption capabilities of the COFs. This research provides guidance for the rational design of iodine adsorbents for the efficient capture of iodine in spent fuel reprocessing.