Leveraging Low-Pressure-Induced Structural Distortions in Unsubstituted Imidazole-Incorporated Zeolitic Imidazolate Framework-8 Nanostructures for Permanent Trapping of Iodine Gas

The permanent confinement of guest molecules within porous nanomaterials is of paramount importance, particularly for toxic gases, such as radioactive iodine (I2). This study aims to develop and evaluate an advanced nanoporous framework capable of achieving irreversible I2 trapping. For this purpose, we systematically investigated the I2 capture and irreversible trapping capacities of both prototypical zeolitic imidazolate framework-8 (ZIF-8) and unsubstituted imidazole (Im)-incorporated ZIF-8. The latter was synthesized via a rationally optimized method, termed delayed linker addition (DLA)-solvent-assisted linker exchange (SALE) integrated approach (DSIA), which enables one-pot synthesis at low temperature, and eliminates the complexity of conventional postsynthetic modifications. Using this method, we achieved a maximum Im loading of 58 mol %, which is the highest for a low-temperature linker exchange strategy. Significantly, Im incorporation did not disrupt the sodalite topology or thermal stability of ZIF-8; instead, it reduced the framework’s flexibility, as confirmed by N2 gas adsorption measurements. The Im-incorporated ZIF-8 loaded with I2 was partially amorphized by pressure treatment for permanent I2 trapping. Thermogravimetric measurements confirmed that the I2 release step was absent for the partially amorphized Im-incorporated ZIF-8, indicating its permanent trapping. Positron annihilation lifetime spectroscopy was used to study the pressure-induced changes in the pore architecture of the frameworks. It revealed that Im-incorporated ZIF-8 exhibits an easily distortable pore network compared with the prototypical form. It is proposed that pressure-induced amorphization triggers permanent distortion of the central cavity and a significant loss in pore interconnectivity, resulting in the permanent trapping of I2. Remarkably, this study introduces a versatile and straightforward synthesis strategy that enables secondary linker incorporation into ZIF-8 under ambient conditions. It eliminates the need for complex postsynthetic modifications and provides a promising nanoporous material for the permanent confinement of toxic guest molecules within the pore network.