Encapsulation of Nitrogen-Rich Imidazole/Pyrazole in an Indium-Based Metal–Organic Framework for Organic Iodide Adsorption

Abstract Nitrogen-rich organic small molecules are frequently incorporated into porous materials to improve their adsorption performance. To investigate the effect of nitrogen-rich imidazole/pyrazole compounds encapsulated within metal–organic frameworks (MOFs) on organic iodide adsorption, 2-methylimidazole, 1-vinylimidazole, and pyrazole were separately incorporated into the pores of SHF-61 via the thermal diffusion method, yielding SHF-61-based composites (namely, 2-MI@SHF-61, Vlm@SHF-61, and Pyr@SHF-61). These composites exhibited remarkable static CH3I adsorption capacities of 1421, 1290, and 1149 mg/g at 75 °C, representing 2.40-, 2.18-, and 1.94-fold enhancements relative to pristine SHF-61. Likewise, their static C2H5I adsorption capacities at 75 °C were increased by 3.33-, 2.28-, and 2.05-fold, respectively. Noteworthily, the static organic iodide adsorption capacities of SHF-61-based composites surpass those of most previously reported MOF-based adsorbents. Further analysis of the adsorption mechanism of SHF-61-based composites toward organic iodides revealed that the adsorption process involves the formation of I3– anions through charge-transfer interactions as well as N-methylation/ethylation reactions. Our study demonstrates that the encapsulation of nitrogen-rich imidazole/pyrazole compounds within MOFs effectively enhances the organic iodide adsorption performance of materials, providing valuable guidance for the rational design of high-performance organic iodide adsorbents.