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Molecular sieving realized with ZIF-8/Matrimid® mixed-matrix membranes

2010; Elsevier BV; Volume: 361; Issue: 1-2 Linguagem: Inglês

10.1016/j.memsci.2010.06.017

1873-3123

Ma. Josephine C. Ordoñez, Kenneth J. Balkus, John P. Ferraris, Inga H. Musselman,

Covalent Organic Framework Applications

Zeolitic imidazolate frameworks (ZIFs), that have the potential for gas separation, were used as additives in mixed-matrix membranes (MMMs). ZIF-8, which exhibits the sodalite topology, is composed of zinc (II) ion clusters linked by imidazolate ligands. The ZIF-8 pore aperture is 3.4 Å allowing it to readily absorb small molecules such as H2 and CO2. ZIF-8/Matrimid® MMMs were fabricated with loadings up to 80% (w/w), which are much higher than the typical loadings achieved with select zeolite materials. Only at the highest loading did the ZIF-8/Matrimid® MMM show a loss of mechanical strength, leading to a decrease in flexibility. The ZIF-8/Matrimid® MMMs permeability properties were tested for H2, CO2, O2, N2, CH4, C3H8, and gas mixtures of H2/CO2 and CO2/CH4. The permeability values increased as the ZIF-8 loading increased to 40% (w/w). However, at higher loadings of 50% and 60% (w/w), the permeability decreased for all gases, and the selectivities increased consistent with the influence of the ZIF-8 additive. The ideal selectivities of gas pairs containing small gases, such as H2/O2, H2/CO2, H2/CH4, CO2/CH4, CO2/C3H8, and H2/C3H8, showed improvement with the 50% (w/w) ZIF-8 loading, demonstrating a transition from a polymer-driven to a ZIF-8-controlled gas transport process. In control experiments using as-synthesized ZIF-8 with filled pores, there was no transition at 50% (w/w) loading. This may be the first example of an MMM wherein molecular sieving is evident and suggests that additive loadings >50% (w/w) may be required to observe this effect in MMMs.