Abstract
Two-dimensional metal–organic framework (MOF) nanosheets with molecular sieving properties and unique dimensional advantages are highly desired as polymer fillers for gas separation applications. Regarding polymer-supported MOF membranes, it is crucial to enhance the adhesion between the polymeric substrate and the MOF component and avoid MOF particle agglomeration. In this study, hydrophobic, embedded nanoporous nanosheets of a 2D zeolitic imidazolate framework synthesized using zinc salt and 2-methylimidazole (Hmim) aqueous solution (ZIF-L) were incorporated into a carboxymethyl cellulose (CMC) solution to form a steady mixed aqueous suspension through one-step solution blending. This prepared the composite membranes with a fine dispersion of ZIF-L nanosheets (up to loadings of 52.88 vol %) and good adhesion within the highly dense structural CMC matrix due to the strong interactions between ZIF-L and CMC, as confirmed by FTIR, Zeta potential, XPS, and SEM analysis. The potential advantages of CMC over classic polymer matrices used for gas separation mainly include: (a) Good interaction, (b) high dispersion of ZIF-L nanosheets, (c) the gas barrier nature of the CMC membrane, and (d) a facile water-based synthetic process. Based on the molecular sieving effect of ZIF-L and the gas barrier nature of the CMC matrix, gas permeation tests (H2, CO2, N2, CH4) of the mixed membrane showed a great improvement in gas selectivities compared with the CMC membrane and the reported pure ZIF membranes.
Highlights
Advantages, including high mass transfer efficiency as well as easy processing and operation conditions, make membranes competitive gas separation materials in industrial fields [1]
The results showed that carboxymethyl cellulose (CMC) was an effective polymer capping ligand for stabilizing zeolitic imidazolate framework (ZIF)-L nanosheets in water due to the formation of metal–organic framework (MOF)–CMC complexes in water, leading to a composite membrane with a uniform structure
The membranes were flexible and we found that the mixed membranes with higher contents of ZIF-L nanosheets became white in color and opaque (Figure 7c,d)
Summary
Advantages, including high mass transfer efficiency as well as easy processing and operation conditions, make membranes competitive gas separation materials in industrial fields [1]. Membrane-based H2 /CO, H2 /N2 , and H2 /CH4 separations, air separation, and natural gas purification applications have been used in many industrial fields [2]. Inorganic porous membranes can be used to separate gas molecules through aperture distinction mechanisms [4]. As a new generation of inorganic molecular sieving materials, metal–organic frameworks (MOFs) are an alternative for gas separation applications due to their well-defined pores and ultrahigh porosity structure. The zeolitic imidazolate framework (ZIF) is a family of MOF that presents zeolite-like structural topologies with excellent thermal and chemical stabilities [5]. ZIF-8 is a stable MOF constructed from tetrahedral zinic ions connected with large cavities of 11.6 Å, which further consist
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