A High‐Performance Gas‐Separation Membrane Containing Submicrometer‐Sized Metal–Organic Framework Crystals

Abstract

Metal-organic frameworks (MOFs) are an emerging class of nanoporous materials comprising metal centers connected by various organic linkers to create one-, two-, and threedimensional porous structures with tunable pore volumes, surface areas, and chemical properties. Several thousand MOF materials have been synthesized and their numbers continue to grow rapidly. [1] MOFs are predicted to be highly attractive for application in gas-separation membranes [2] and also have a range of other potential applications, for example in selective gas adsorption, [3] hydrogen storage, [4] catalysis, [5] and sensing. [6] Recently, thin continuous MOF membranes for gas separation have been reported by several authors using MOFs such as MOF-5, [7] HKUST-1 (Cu 3 (BTC) 2 ), [8] Cu-(hfipbb)(H 2 hfipbb) 0.5 , [9] and ZIF-8.[10] However, the gas-permeation properties (permeability and selectivity) have so far not been found to be technologically attractive. This may have several reasons, such as membrane defects and related processing issues, use of MOFs with low selectivity, and unfavorable orientation of crystals in the membrane.An alternative route to high-performance MOF membranes is to incorporate them into polymers to obtain nanocomposite (mixed-matrix) membranes. The incorporation of nanoporous molecular sieves such as zeolites into polymeric membranes has attracted much attention, since one can in principle combine the size/shape selectivity of nanoporous materials with the processibility and mechanical stability of polymers.[11] However, zeolite/polymer composite membranes often have defective morphologies characterized by void spaces between the zeolite particles and the polymeric matrix, leading to poor gas-separation performance since the gas molecules bypass the zeolite particles. [11,12] Recent approaches to address the issue of interface compatibilization are emerging.[13] On the other hand, the use of MOFs in mixed-matrix membranes provides several potential advantages over zeolites. The control of MOF/polymer interface morphology is easier than that of the zeolite/polymer interface, since the organic linkers in MOFs have better affinity with polymer chains than the inorganic zeolites do, and the surface properties of MOFs can be easily tuned by functionalization with various organic molecules if necessary. [14] In general, MOFs also have higher pore volumes and lower density than zeolites, and hence their effect on the membrane properties can be greater for a given mass loading. Recently, several MOF mixed-matrix membranes such as Cu-BPY-HFS (Cu-4,40-bipyridine hexafluorosilicate) in Matrimid, [15] HKUST-1 in poly(sulfone), [16] MOF-5 in Matrimid, [17] and Cu-TPA (terephthalic acid) in poly(vinyl acetate) [18] have been reported. Although a high degree of MOF/polymer adhesion (as characterized by scanning electron microscopy) was found, the gas-separation performance of these membranes was not high. In addition to the control of interface morphology, the selection of appropriate MOF/polymer pairs is indispensable fo...

High performance mixed matrix membranes (MMMs) composed of ZIF-94 filler and 6FDA-DAM polymer

“…Nevertheless, the common feature is a significant increase in CO 2 permeability observed by the addition of the filler particles in the 6FDA-DAM polymer matrix. In some cases, there is a selectivity increase due to either molecular sieving [37] or to solubility increase ( [36]. Zhang et al went a step further and ZIF-8/6FDA-DAM mixed-matrix hollow fiber membranes were prepared with ZIF-8 nanoparticle loading up to 30 wt% [61].…”

“…In our case, a commercially available high flux 6FDA-DAM polyimide was selected for membrane preparation. The preparation of 6FDA-DAM MMMs by the addition of several fillers such us NH 2 -MIL-53(Al) [34], ZIF-11 [35], CPO-27(Mg) [36], ZIF-90 [37] and ZIF-8 [38] has been reported in literature. Membrane properties for gas separation are shown and compared with our MMM in the results and discussion section of this paper ( Table 1).…”

Thermal and mechanical stability of zeolitic imidazolate frameworks polymorphs

“…[1][2][3][4] ZIFs have recently gained considerable attention for their potential applications, e.g., in domains such as CO 2 capture, 5 sensing, 6 encapsulation and controlled delivery, 7 and fluid separation. [8][9][10][11] ZIFs as a family are often thought of as having specific advantages over MOFs in general. It is often stated that they inherit desirable qualities from both the MOF and zeolite worlds: the tunable porosity, structural flexibility, and the functionalization of the internal surface of the MOFs, as well as the thermal, mechanical, and chemical stability of the zeolites.…”

Origins and Evolution of Inorganic-Based and MOF-Based Mixed-Matrix Membranes for Gas Separations

“…By comparing the apparent diffusivities of the gases in the MMM with those in the pure polymer, the authors concluded that the gases were diffusing through the MOF and not through voids or defects at the MOF-polymer interface, and that a true mixed-matrix effect was achieved. This same year, T.-H. Bae, et al reported on the first ZIF-based MMM incorporating ZIF-90 crystals (Figure 15) into Ultem™, Matrimid ® , and 6FDA-DAM polyimides [127]. Submicrometer-sized ZIF-90 crystals synthesized using methanol and deionized water as nonsolvents ( Figure 18) were incorporated in these polyimides (Figure 19) a 15 wt % ZIF loadings.…”

“…Gas transport in these MMMs improved with increased loadings, bringing the membranes to or above the upper bound. In 2010, T.-H. Bae, et al prepared the first ZIF-based MMM incorporating ZIF-90 into Ultem™, Matrimid ® , and 6FDA-DAM [127]. A few years later, in 2015, E. V. Perez, et al reported that they had successfully tested (Al) NH 2 -MIL-53/VTEC™ MMMs at pressures up to 30 bar and 300 • C, achieving H 2 /CO 2 mixture selectivities of 8 [128].…”