Rapid One-pot Microwave Synthesis of Mixed Linker Hybrid Zeolitic-imidazolate Framework Membranes for Tunable Gas Separations
Febrian Hillman (1), Jordan Brito(1), Hae-Kwon Jeong*(1,2)
1. Artie McFerrin Department of Chemical Engineering and
2. Department of Material Science and Engineering, Texas A&M University, 3122 TAMU, College Station, Texas 77843-3122, United States.
*Corresponding author: email@example.com
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. One alternative solution that can reduce energy consumption is through membrane separation using porous solid material such as metal organic frameworks (MOFs). Zeolitic-imidazolate frameworks (ZIFs), a subclass of MOFs, in particular have attracted many attentions due to their chemical/thermal stabilities, their ultra-miroporosities, and high surface area when compared to other MOFs material. ZIFs are frameworks consisting transition metals bridged by imidazolate-derived ligands. A common drawback for membrane gas separation is the limited availability of pore size and functionalities. Furthermore, the slow fabrication of MOF membranes restricts their commercialization. Studies have shown that through mixing linkers, one can continuously tune the ZIFs (termed hybrid ZIFs) properties to match with the characteristic of specific gas mixture.
Herein we report a rapid one-step microwave-assisted synthesis of mixed linker ZIF-7-8 membranes in under ~ 90 seconds. ZIF-7-8 consists of Zn2+ metal nodes bridged by a mixture of benzimidazolate (bIm, ZIF-7 linker) and 2-methylimidazolate (mIm, ZIF-8 linker) linkers. To the best of our knowledge, this is the fastest synthesis of any polycrystalline MOF membranes reported up to now. Furthermore, the gas separation performances (separation factor and permeance) of hybrid ZIF-7-8 membranes were systematically tuned by varying the bIm-to-mIm ratio incorporated into the framework. The unprecedentedly rapid synthesis of ZIF-7-8 membranes with tunable molecular sieving properties is an important step forward for their practical applications in separations of gas mixtures of interest.
Keywords: gas separation membranes, tunable gas separations, hybrid metal-organic frameworks, microwaves