This study presents a novel approach for fabricating ZIF-8 membranes supported on α-alumina hollow fibers through the introduction of a graphene oxide (GO) gutter layer and the application of zinc oxide (ZnO) Atomic Layer Deposition (ALD). The method successfully addressed key challenges, including excessive precursor penetration and membrane thickness. The introduction of the GO layer and subsequent ZnO ALD treatment significantly reduced membrane thickness to approximately 300 nm and eliminated delamination issues between the GO layer and the alumina support. The optimized membranes demonstrated enhanced propylene permeance, with values approximately three times higher than those of membranes without GO, and achieved higher separation factors, indicating minimal inter-crystalline defects. Notably, the GO layer influenced the microstructure, leading to an increase in permeance with rising temperatures. These findings highlight the potential of this strategy for developing high-performance ZIF-8 membranes for gas separation applications.
Abstract Although the pore structures and gas transport properties of metal‐organic frameworks (MOFs) have been tuned mainly by modifying the framework building blocks, a pore‐tuned zeolitic imidazolate framework (ZIF)‐8 layer is directly grown on graphene oxide nanoribbons (GONR)‐treated polymer substrate. Oxygen‐containing functional groups and GONR dangling‐carbon bonds facilitated the spontaneous growth of ZIF‐8 oriented to the (100) grain on the GONR surface and also enhanced the rigidity by strongly anchoring the ZIF‐8 layer by metal‐carbon chemisorption. Gas permeation and molecular simulation results confirmed that the effective aperture size of ZIF‐8 is adjusted to 3.6 Å. As a result, ultrafast H 2 permeance of 7.6 × 10 −7 mol m −2 Pa s is achieved while blocking large hydrocarbon molecules. In particular, the membrane showed exceptionally enhanced hydrogen selectivity for the mixture separation than ideal selectivity, owing to the competitive transport between H 2 and large hydrocarbon molecules, and the separation performance surpassed those of ZIF membranes previously fabricated on polymeric supports.
Nanoporous zeolitic imidazolate frameworks (ZIFs) form structural topologies equivalent to zeolites. ZIFs containing only one type of imidazole linker show separation capability for limited molecular pairs. We show that the effective pore size, hydrophilicity, and organophilicity of ZIFs can be continuously and drastically tuned using mixed-linker ZIFs containing two types of linkers, allowing their use as a more general molecular separation platform. We illustrate this remarkable behavior by adsorption and diffusion measurements of hydrocarbons, alcohols, and water in mixed-linker ZIF-8(x)-90(100-x) materials with a large range of crystal sizes (338 nm to 120 μm), using volumetric, gravimetric, and PFG-NMR methods. NMR, powder FT-Raman, and micro-Raman spectroscopy unambiguously confirm the mixed-linker nature of individual ZIF crystals. Variation of the mixed-linker composition parameter (x) allows continuous control of n-butane, i-butane, butanol, and isobutanol diffusivities over 2-3 orders of magnitude and control of water and alcohol adsorption especially at low activities.
Gas Separation In their Communication on page 16390 ff., K. Eum, M. Tsapatsis et al. describe the separation of oxygen from air by modified ZIF membranes. The permeation properties of the membranes are reversible and can be tailored to suit their application.
Metal-organic frameworks (MOFs), which are highly ordered structures exhibiting sub-nanometer porosity, possess significant potential for diverse gas applications. However, their inherent insulative properties limit their utility in electrochemical gas sensing. This investigation successfully modifies the electrical conductivity of zeolitic imidazolte framework-8 (ZIF-8) employing a straightforward surface oxidation methodology. A ZIF-8 polycrystalline layer is applied on a wafer-scale oxide substrate and subjects to thermal annealing at 300 °C under ambient air conditions, resulting in nanoscale oxide layers while preserving the fundamental properties of the ZIF-8. Subsequent exposure to NO
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