Electronic Structure Modulation in Covalent Organic Frameworks through Ethynyl Positioning for Enhanced Low-Concentration Iodine Capture

The capture of low-concentration iodine under industrial conditions poses a significant challenge. The introduction of electron-rich ethynyl groups into covalent organic frameworks (COFs) can enhance the iodine adsorption performance. However, the influence of ethynyl group positioning (framework-embedded vs pore-pendant) in COFs on iodine adsorption performance remains unclear. Herein, three COFs including framework-embedded ethynyl-COF (TPEB-TAPB-COF), pore-pendent ethynyl-COF (BPO-TAPB-COF), and non-ethynyl COF (TFPB-TAPB-COF) were synthesized. Under saturated iodine vapor conditions, the iodine capture capacity of TPEB-TAPB-COF reached 8.65 g/g, demonstrating the superior performance of framework-embedded ethynyl groups via enhanced electron delocalization. By contrast, methylene-linked pore-pendant groups limited the delocalization due to the sp³-hybridization of methylene, reducing adsorption capacity. Under simulated industrial conditions (150 °C, 150 ppmv of I₂), the TPEB-TAPB-COF demonstrated an exceptional iodine adsorption capacity (0.493 g/g), exceeding most porous materials. This work provides a new design principle for developing high-performance radioactive iodine capture materials.