Carbon nanotube supported oriented metal organic framework membrane for effective ethylene/ethane separation.

Ruicong Wei,Cailing Chen,Zhen Li,Yu Han,Zhiping Lai,Xinglong Dong,Dongwei Lu,Xiang Li,Zongyao Zhou,Xiaowei Liu,Youyou Yuan

doi:10.1126/sciadv.abm6741

Ruicong Wei, Cailing Chen + Show 9 more

Open Access

https://doi.org/10.1126/sciadv.abm6741

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Abstract

Zeolitic imidazolate framework 8 (ZIF-8) is effective for C3H6/C3H8 separation because of the “sieving effect” of a six-membered (6-M) window. Here, we demonstrate that ZIF-8 is a versatile material that could effectively separate C2H4 from C2H6 via its 4-M window along the <100> direction. We established a facile and environmentally friendly carbon nanotube (CNT)–induced oriented membrane (CNT-OM) approach to fabricate a {100}-oriented ZIF-8 membrane (100-M). In this approach, 2-methyimidazole was anchored onto the CNT surface followed by 3-hour in situ growth in aqueous solution at room temperature. The obtained 100-M, whose 4-M window is aligned along the transport pathway, showed ~3 times higher C2H4/C2H6 selectivity than a randomly oriented membrane. Thus, this work demonstrates that the membrane orientation plays an important role in tuning selectivity toward different gas pairs. Furthermore, 100-M exhibited excellent mechanical stability that could sustain the separation performance after bending at a curvature of ~109 m−1.

Highlights

Metal organic frameworks (MOFs), a type of microporous polycrystalline materials, have drawn research attention owing to its high porosity, tunable structural and chemical properties, and ease of synthesis [1, 2]
At 10 min, the cement-filled carbon nanotube (CNT) surface has been fully covered with a layer of loosely packed Zeolitic imidazolate framework 8 (ZIF-8) crystals (Fig. 2B) with rhombic dodecahedron morphology (Fig. 2H)
Combing all the x-ray diffraction (XRD) studies of different configurations and crystallographic preferred orientation (CPO) index, we can confirm that the highly {100} out-of-plane oriented ZIF-8 membrane has been obtained within 3 hours of synthesis at room temperature

Summary

Introduction

Metal organic frameworks (MOFs), a type of microporous polycrystalline materials, have drawn research attention owing to its high porosity, tunable structural and chemical properties, and ease of synthesis [1, 2]. MOFs have one or multiple channels in different crystallographic orientations. Each crystallographic orientation has a specific window aperture. The window aperture functions to discriminate the molecules with diameters beyond the aperture size. MOFs generally have the window aperture at the gas molecule scale, making them good candidates to be fabricated into membranes for gas separations. Most of the reported polycrystalline MOF membranes are composed of crystals with random orientations. Oriented polycrystalline MOF membranes are more desirable as they could potentially minimize the grain boundary defects and regulate gas separation performance by tuning the crystallographic orientation relative to the substrate [3,4,5,6]

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