Abstract
In this paper, we propose mixed metal ions in the node of the zeolitic imidazolate framework (ZIF) structure. The hybrid metal ZIF is formed for the gas separation of hydrogen and carbon dioxide. In the first stage, the nanoparticles were prepared as a coating on a substrate, and acting as secondary growing nuclei. The hybrid metal ZIF structures were characterized by X-ray diffractometry (XRD) and Fourier transform infrared spectroscopy (FTIR). N2 adsorption–desorption isotherms determined surface area, and scanning electron microscopy (SEM) was used to observe the microstructure and surface morphology. The hybrid metal ZIF-8-67 powder had the largest surface area (1260.40 m2 g−1), and the nanoparticles (100 nm) could be fully dense-coated on the substrate to benefit the subsequent membrane growth. In the second stage, we prepared the hybrid metal ZIF-8-67 membrane on the pre-seeding substrate with mixed metal nanoparticles of cobalt and zinc, by the microwave hydrothermal method. Cobalt ions were identified in the tetrahedral coordination through UV–Vis, and the membrane structure and morphology were determined by XRD and SEM. Finally, a gas permeation analyzer (GPA) was used to determine the gas separation performance of the hybrid metal ZIF-8-67 membrane. We successfully introduced zinc ions and cobalt ions into the ZIF structure, where cobalt had a strong interaction with CO2. Therefore, GPA analysis showed an excellent H2/CO2 separation factor due to lower CO2 permeability. The CO2 permeance was ~0.65 × 10−8 mol m−2 s−1 Pa−1, and the separation factors for H2/CO2 and H2/N2 were 9.2 and 2.9, respectively. Our results demonstrate that the hybrid metal ZIF-8-67 membrane has a superior H2/CO2 separation factor, which can be attributed to its very high specific surface area and structure. Based on the above, hybrid metal ZIF-8-67 membranes are expected to be applied in hydrogen or carbon dioxide gas separation and purification.
Highlights
Zeolitic imidazolate frameworks (ZIFs) are members of a new class of hybrid organic–inorganic materials, called metal–organic frameworks (MOFs), which have relatively regular pores and significant advantages: in a higher specific surface area, ranging from micropores to mesopores; designable structure characteristics, including the skeleton, pore shape, pore size, and surface chemical properties [1]
We report the synthesis of hybrid metalZIF-8-67 membranes, c-oriented by the microwave hydrothermal method
The results showed that the whole crystal phase was the same as that of the zeolitic imidazole framework-8 (ZIF-8) membrane, and no other crystal phase was derived
Summary
Zeolitic imidazolate frameworks (ZIFs) are members of a new class of hybrid organic–inorganic materials, called metal–organic frameworks (MOFs), which have relatively regular pores and significant advantages: in a higher specific surface area, ranging from micropores to mesopores; designable structure characteristics, including the skeleton, pore shape, pore size, and surface chemical properties [1]. ZIFs have ordered porous structures with hybrid frameworks, which consist of inorganic metal ions or metal clusters coordinated with organic imidazolate ligands [2,3]. Materials 2020, 13, 5009 designability of the organic ligands, and the directionality of the metal ion, offer conventional adsorptive properties, such as storage, separation, and catalysis, and other physical/chemical functions integrated into the frameworks. They have a highly flexible structure, including pore size and surface properties that can be rationally designed. The structural composition of ZIFs consists of metal atoms (such as Zn and Co) regularly connected with ditopic imidazolate (Im), or functionalized Im, and N atoms to form neutral frameworks [4]
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