Herein we report a new microwave-assisted synthetic strategy to rapidly prepare hybrid zeolitic–imidazolate frameworks (ZIFs): ZIFs with mixed metal centers and/or mixed linkers. The microwave-based method significantly shortens synthesis time, produces a higher yield, substantially reduces the amounts of ligands, and eliminates the use of deprotonating agents. The X-ray diffraction pattern reveals that mixed metal CoZn–ZIF-8 (i.e., ZIF-8 with both Co and Zn centers) maintains the sodalite (SOD) zeolitic topology from the 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 of IR bands 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, mixed metal CoZn–ZIF-8 with a Co/Zn ratio of ∼1 was grown as membranes on porous α-Al₂O₃ supports, showing a higher propylene/propane separation factor (∼120) when compared to pure Zn–ZIF-8 membranes (∼63) prepared by a similar method.

Peer reviewed article authored by (Baek M, Chung HE, Yu J, Lee JA, Kim TH, Oh JM, Lee WJ, Paek SM, Lee JK, Jeong J, Choy JH, Choi SJ). Read article or submit your manuscript for publishing.