(198d) Rapid Microwave-Assisted Synthesis of Hybrid Zeolitic-Imidazolate Frameworks | AIChE

(198d) Rapid Microwave-Assisted Synthesis of Hybrid Zeolitic-Imidazolate Frameworks


Hillman, F. - Presenter, Texas A&M University
Zimmerman, J., Texas A&M
Paek, S. M., Kyungpook National University
Hamid, M., Texas A&M University
Lim, W. T., Kyungpook National University
Jeong, H. K., Texas A&M Univeristy
Separating a crude component into a more valuable purer product is a major part of many industrial chemical plants. Typically these processes utilize distillation, which account to 10 – 15 % of world’s energy consumption.1 One alternative solution that can reduce energy consumption up to 90 % relative to distillation is through membrane separation using porous solid material such as zeolites and metal organic frameworks (MOFs).2 Zeolitic-imidazolate frameworks (ZIFs),3 a subclass of MOFs, in particular have attracted many attentions due to their chemical/thermal stabilities, their ultra-microporosities, and high surface area when compared to other MOFs material.3 ZIFs possess zeolite-like topologies in which the tetrahedral Si or Al and the bridging O in zeolite structure are replaced by transition metals (such as Zn,3 Co,4 and Cd5) and imidazolate-derived ligands. A common drawback for membrane gas separation is the limited availability of aperture pore size and functionalities of the porous materials. Studies have shown that through mixing metals6,7 and ligands,8,9 one can continuously tune the MOFs/ZIFs (termed hybrid ZIFs) properties to match with the characteristic of specific gas mixture. However, the common synthesis of hybrid ZIFs has generally been through slow diffusion techniques,4,10 conventional hydrothermal,7,11 and solvothermal methods,9,12,13 requiring several hours up to days of synthesis time. In addition, the yields of those synthesis protocols are often low, an economical issue for hybrid ZIFs to be used in a large industrial scale.

Herein we plan to present a new microwave-assisted synthetic strategy to rapidly prepare hybrid zeolitic-imidazolate frameworks (ZIFs): ZIFs with mixed metal centers and/or mixed linkers.14 The microwave-based method significantly shortens synthesis time, produces higher yield, substantially reduces the amount of ligand, and eliminates the use of deprotonating agents. X-ray diffraction pattern reveals a mixed metal CoZn-ZIF-8 (i.e., ZIF-8 with both Co and Zn centers) maintains the sodalite (SOD) zeolitic topology from ZIF-8 parent. Elemental mapping using Energy-dispersive X-ray spectroscopy (EDS) and electronic/geometric information obtained from X-ray absorption spectroscopy (XAS) confirm the uniform distribution of tetrahedral Co and Zn metal centers within the same framework of the mixed-metal ZIF. The metal to nitrogen (M-N) stretching frequencies on IR band were observed to be systematically blue-shifted as the Co/Zn ratio in the mixed metal ZIF increases. Furthermore, for the first time, a hybrid ZIF with both mixed metal centers (Co and Zn) and mixed linkers (2-methylimidazolate and benzimidazolate) was prepared through one-step microwave synthesis. Finally, a mixed metal CoZn-ZIF-8 with the Co/Zn ratio of ~ 1 was grown as membranes on porous α-Al2O3 supports, showing higher propylene/ propane separation factor (~120) when compared to pure Zn-ZIF-8 membranes (~63) prepared with similar method.


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14. Hillman, F.; Zimmerman, J. M.; Paek, S.-M.; Hamid, M. R. A.; Lim, W. T.; Jeong, H.-K. Rapid microwave-assisted synthesis of hybrid zeolitic-imidazolate frameworks with mixed metals and mixed linkers. J. Mater. Chem. A 2017, 5, 6090-6099.