Two isomeric metal–organic frameworks bearing stilbene moieties for highly volatile iodine uptake

Abstract

Efficient, green, and economical removal of radioactive iodine (I₂) has drawn worldwide attention for the safe development of nuclear energy. Metal–organic frameworks (MOFs) have been demonstrated to be potential candidates for I₂ capture. Herein we report the synthesis of two novel isomeric MOFs bearing stilbene moieties for exceptionally high I₂ adsorption. [Cd(hsb-2)(tsbdc)]·0.5DMF (HSB-W8) and Cd(hsb-2)(tsbdc) (HSB-W9), which exhibit two-dimensional and twofold interpenetrated three-dimensional structures, respectively, have been assembled from hydrogenated Schiff base ligands, hsb-2 (1,2-bis(4′-pyridylmethylamino)-ethane) and trans-stilbene-4,4-dicarboxylate (tsbdc), and Cd(NO₃)₂ by the diffusion method. Such isomers arise from the different conformations of hsb-2 ligands controlled by diffusion temperatures. The π-electron-rich stilbene moieties render these Cd-MOFs ideal platforms for I₂ capture. The adsorption capacities of HSB-W8 and HSB-W9 in I₂ vapor at room temperature can reach up to 2.32 and 1.92 g g⁻¹, respectively, which are comparable to the best-performing MOF materials reported so far. Furthermore, pseudo-second-order (PSO) kinetic model analysis, Fourier transform infrared (FT-IR) spectroscopy, Raman spectral analysis, density functional theory (DFT) calculations, and control experiments were performed to shed light on host–guest interactions and the iodine adsorption mechanism. This work develops a rational strategy to design and synthesise functional MOF materials for iodine adsorption.