Synthesis, Characterization, and Tunable Adsorption and Diffusion Properties of Hybrid ZIF-7-90 Frameworks

Hybrid zeolitic imidazolate frameworks (ZIFs), containing more than one type of imidazolate linker, can allow highly tunable molecular sieving and adsorption. Their crystallization becomes more challenging when the end-member (single-linker) ZIFs crystallize in different crystal systems. We demonstrate the controlled synthesis and detailed characterization of hybrid ZIF-7-90 frameworks containing linkers of ZIF-7 (rhombohedral) and ZIF-90 (cubic). ZIF-7-90 materials with SOD-type topology are obtained in three crystalline phases depending on the linker composition and synthesis technique. The effect of synthesis conditions on the activation-induced phase transition from rhombohedral to other topologies is studied. Nitrogen physisorption at 77 K and CO2 physisorption at 273 K shows the tunability of the pore-size distribution and the framework flexibility as a function of framework composition. Measurements of water adsorption and butane isomer diffusion illustrate the tunability of diffusivity over seven orders of magnitude and control of hydrophobic to hydrophilic adsorption behavior. © 2015 American Institute of Chemical Engineers AIChE J, 62: 525–537, 2016