Design and Synthesis of Stable Sp2-Carbon-Linked Two-Dimensional Conjugated Covalent Organic Framework for Efficient Capture of Radioactive Iodine

Abstract

The ingenious design of sp 2 -carbon-linked fully π-conjugated covalent organic frameworks ( sp 2 - c -COFs) with a periodic pore structure and high chemical stability, is vital. However, this remains a significant challenge owing to the poor reversibility of the coupling reactions. Here two novel isoreticular crystalline and highly porous two-dimensional (2D) sp 2 - c -COFs (COF- p -NEU1 and COF- p -NEU2) are designed and synthesized via a base-catalyzed Knoevenagel polycondensation reaction based on the [ C 2 + C 3 ] topology diagram. As-prepared polycrystalline COF- p -NEU1 (with 1,3,5-tris(p-formylphenyl)benzene) and COF- p -NEU2 (with 1,3,5‐tris‐(4‐formylphenyl) triazine) exhibit long-range ordered structures, well-defined nanochannels, and favorable chemical stable, which endow the promising capture performance of COF materials. Meanwhile, the two sp 2 -c -COF can provide abundant functional units to promote the capture of I 2 due to introducing mass nitrogen species into the building block, which will enhance electron-pair the effect and host-guest interactions. Therefore, the two nitrogen-rich 2D sp 2 - c -COFs exhibit a high iodine uptake capacity for iodine vapor and iodine in cyclohexane with 4.58 g g -1 and for 1.31 g g -1 COF- p -NEU1 and 5.87 g g -1 and 1.51 g g -1 for COF- p -NEU2 at 348 K. The results of this study provide a potential path for the design and synthesis of novel sp 2 -c -COFs materials with high chemical stability and demonstrate the high potential of sp 2 -c -COF for the capture of radioactive contaminants and related applications.

Keywords: Covalent organic framework, Iodine, capture