(593e) A New Approach for Ultra-thin Tunable Molecular Sieve Membranes for High-resolution Custom Gas Separations

Molecular-sieving zeolitic imidazolate frameworks (ZIFs), a sub-class of metal-organic frameworks (MOFs), offer unique opportunities in gas separations primarily due to their ultra-micropores (pores smaller than 5 Å) and their unusual thermal/chemical stabilities. However, there exist both fundamental materials limitations and processing challenges: one major fundamental materials challenge is that only very few ZIF/MOF materials show promising molecular sieving properties for industrially important gas separations. The reason is that an exact one-to-one size match between the aperture size and the molecules of interest is required. However, as with any other crystalline porous materials such as zeolites, when the size disparity of the gas molecules of interest is too small as is the case for many challenging separations, ZIFs (MOFs in general) with suitable aperture size are not always available. Processing challenges include slow batch crystallization, grain boundary defects, expensive porous supports, lack of "generalâ? method, and reproducibility issues. Though some of these processing challenges have been recently addressed, there still remains an ultimate challenge for the practical applications of ZIF membranes, which is the high cost of membranes and membrane processes as compared to polymeric membranes. One can bring down the cost of membranes and membrane processes by significantly improving the productivity of membranes by 1) substantially reducing membrane thickness and 2) increasing membrane area (note that the membrane productivity is given as the following equation: , where P_A, l, and A are the permeability of gas A, membrane thickness, and membrane area, respectively).

In this talk, I would like to discuss a completely new approach to address both materials and processing challenges mentioned above. The approach is based on the labile coordination chemistry of metal-organic framework materials, enabling to post-synthetically design, engineer, and modify the fine structures of ZIFs such that the aperture sizes of ZIFs can be finely tuned for custom gas separations as well as the thicknesses of their membranes can be in sub 10 nanometer range.