Multifunctional and Hierarchical Porous ZIF-8: Amine and Thiol Tagged via Mixed Multivariate Ligand Strategies for Enhanced CO 2 and Iodine Adsorption.

This study demonstrated a simple and innovative way of using the direct de novo synthesis to fabricate the mesoporous structure and diverse functionality of ZIF-8 for environmental cleanup and gas storage applications. By introducing different ligands, we have developed a version of ZIF-8 that could better capture carbon dioxide (CO ₂ ) and iodine. The ZIF-8 was successfully designed to have the hierarchical and mesoporous structure with the functional groups of amine and thiol groups by adjusting the pKa values (from 8 to 12) of ligand instead of the original ligand, 2-methyl imidazole (Hmim, pK _a ~14.2). The modulation of ZIF-8 particle size, porosity, and functional characteristics was achieved through varied ligands and their concentrations, streamlined into a single and room-temperature synthesis condition. The resulting ZIF-8 materials exhibit intricate hierarchical architectures and a high density of functional groups, significantly enhancing molecular diffusion and accessibility. Among the developed materials, ZIF-8-AS, featuring both amine and thiol groups, demonstrates the fastest adsorption kinetics and a twofold increase in iodine adsorption capacity (q _m =1101.5 mg g ^-1 ) compared to ZIF-8 (q _m =514.3 mg g ^-1 ). Furthermore, the hierarchical mesoporosity of ZIF-8-A-10.1 improves CO ₂ adsorption to 1.0 mmol g ^-1 at 298 K, which is 1.3 times higher than that of the microporous ZIF-8.
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