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1. Adsorption of Carbon Dioxide, Methane, and Nitrogen Gases onto ZIF Compounds with Zinc, Cobalt, and Zinc/Cobalt Metal Centers

   https://doi.org/10.1155/2019/6130152  

   Awadallah-F, Ahmed; Hillman, Febrian; Al-Muhtaseb, Shaheen A.; Jeong, Hae-Kwon (December 2019, Journal of Nanomaterials)

   null (Ed.)

   ZIF-8, Co-ZIF-8, and Zn/Co-ZIF-8 are utilized in adsorbing nitrogen (N 2 ), methane (CH 4 ), and carbon dioxide (CO 2 ) gases at temperatures between 25 and 55°C and pressures up to ~1 MPa. Equilibrium adsorption isotherms and adsorption kinetics are studied. The dual-site Langmuir equation is employed to correlate the nonisothermal adsorption equilibrium behavior. Generally, N 2 showed the lowest equilibrium adsorption quantity on the three samples, whereas CO 2 showed the highest equilibrium adsorption capacity. Amid the ZIF samples, the biggest adsorption quantities of N 2 and CH 4 were onto Zn/Co-ZIF-8, whereas the highest adsorption quantity of CO 2 was on ZIF-8. The isosteric heats of adsorbing these gases on ZIF-8, Co-ZIF-8, and Zn/Co-ZIF-8 were examined. Moreover, the overall mass transfer coefficients of adsorption at different temperatures were investigated. 

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2. Influence of doped metal center on morphology and pore structure of ZIF-8

   https://doi.org/10.1557/mrc.2018.221  

   Awadallah-F, Ahmed; Hillman, Febrian; Al-Muhtaseb, Shaheen A.; Jeong, Hae-Kwon (March 2019, MRS Communications)

   null (Ed.)

   Synthesis of ZIF with zinc, cobalt, or copper was carried out by microwaves. The effect of metal center on morphologies and pores of products was studied. Nitrogen adsorption/desorption onto ZIFs was examined by density functional theory. The micro, meso, and macropores of ZIF-8, Zn/Co-ZIF-8, and Cu/ZIF-8 ranged 99.814–99.969%, 0.055–0%, and 0.031–0.130%, respectively. Average pore sizes of ZIF-8, Zn/Co-ZIF-8, and Cu/ZIF-8 are 1.291, 1.194, and 1.164 nm, respectively. Monolayer saturation limits of nitrogen onto ZIF-8, Zn/Co-ZIF-8, and Cu/ZIF-8 were 21.152, 18.943, and 17.784 mmol/g, respectively. Further, the results included densities, total surface areas, total pore volumes, and average particle sizes of ZIF-8, Zn/Co-ZIF-8, and Cu/ZIF-8. 

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3. Effective aperture tuning of a zeolitic-imidazole framework CdIF-1 by controlled thermal amorphization

   https://doi.org/10.1039/d1ta10706b  

   Park, Sunghwan; Jeong, Hae-Kwon (March 2022, Journal of Materials Chemistry A)

   Sodalite zeolitic-imidazole frameworks (ZIFs) show great potential due to their effective aperture sizes suitable for small gas separations. Numerous efforts have, therefore, been made in tuning their effective aperture sizes to control and enhance their molecular sieving properties. Herein, we present a new strategy to finely tune the effective aperture size of CdIF-1, a cadmium-substituted ZIF-8 analogue, based on thermal amorphization. Among several ZIF-8 analogues screened, CdIF-1 was found to be the only one that could be thermally amorphized. The controlled amorphization reduced the long-range structural order while preserving the short-range order, thereby systematically densifying the ZIF structure and consequently affecting its effective aperture. Meanwhile, it was found that amorphization enhanced the flexibility of the framework, resulting in accessible pores at temperatures above 273 K. As compared to its crystalline counterpart, partially amorphized CdIF-1 showed significantly improved diffusion and adsorption selectivities of n -C 4 H 10 /i-C 4 H 10 ( i.e. , 1.5 → 40.7 and 1.1 → 4.9, respectively), likely due to the amorphization-induced tuning of its effective aperture size. 

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4. Plasma-Induced Catalytic Conversion of Nitrogen and Hydrogen to Ammonia over Zeolitic Imidazolate Frameworks ZIF‐8 and ZIF-67

   https://doi.org/https://doi.org/10.1021/acsami.1c03115  

   Fnu Gorky; Jolie M. Lucero; James M. Crawford; Beth Blake; Moises A. Carreon; and Maria L. Carreon (July 2021, ACS applied materials interfaces)

   Microporous crystals have emerged as highly appealing catalytic materials for the plasma catalytic synthesis of ammonia. Herein, we demonstrate that zeolitic imidazolate frameworks (ZIFs) can be employed as efficient catalysts for the cold plasma ammonia synthesis using an atmospheric dielectric barrier discharge reactor. We studied two prototypical ZIFs denoted as ZIF-8 and ZIF-67, with a uniform window pore aperture of 3.4 Å. The resultant ZIFs displayed ammonia synthesis rates as high as 42.16 μmol NH3/min gcat. ZIF-8 displayed remarkable stability upon recycling. The dipole−dipole inter- actions between the polar ammonia molecules and the polar walls of the studied ZIFs led to relatively low ammonia uptakes, low storage capacity, and high observed ammonia synthesis rates. Both ZIFs outperform other microporous crystals including zeolites and conventional oxides in terms of ammonia production. Furthermore, we demonstrate that the addition of argon to the reactor chamber can be an effective strategy to improve the plasma environment. Specifically, the presence of argon helped to improve the plasma uniformity, making the reaction system more energy efficient by operating at a low specific energy input range allowing abundant formation of nitrogen vibrational species. KEYWORDS: nonthermal plasma, plasma catalysis, ammonia synthesis, zeolitic imidazolate frameworks, ammonia adsorption effect 

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5. Carbon Molecular Sieve-derived POC/Mixed-Matrix Membranes for Gas Separation

   kowey, Isha; Rownaghi, Ali (May 2023, North American Membrane Society 2023)

   Membrane-based separations offer the potential for the lowest energy demand requirements of all separation options. Among all nanoporous membranes, the carbon molecular sieves (CMS), metal-organic frameworks (MOFs), and mixed-matrix membranes (MMMs) with angstrom level molecular discrimination properties makes them appealing for separating a wide spectrum of gas-pairs. Here we present results of gas selectivity and diffusion of different gases (C2H6, C2H4, C3H8, C3H6, H2, N2, CO2, and CH4) in porous organic cages (POCs) incorporated into fluorinated copolyimides polymers (FCPs). The FCPs were synthesized by the iridization reaction of fluorinated dianhydrides, nonfluorinated dianhydride, and nonfluorinated diamine. Asymmetric hollow fiber membranes formed by the dry-jet/wet-quench spinning process. Once fresh FCP fibers were synthesized, they were crosslinked with POCs, vacuum dried at 90 °C. We investigated the uptake, gas selectivity and diffusion of different gases (C2H6, C2H4, C3H8, C3H6, H2, N2, CO2, and CH4) over synthesized POC-mixed matrixed membranes (POC-MMM) at 25 °C and pressures up to 1 bar. At 1 bar and 25 °C, C2H6, C2H4, C3H8, C3H6 adsorption capacities reached to 42.61, 2.56, 2.77 and 2.65 mmol/g over POC-MMM, respectively, while CO2, CH4, CO, N2 and H2 adsorption capacities of 1.48, 0.84, 0.33, 0.11, and 0.068 mmol/g, respectively. Furthermore, stable CMS membrane were formed by pyrolysis of POC-MMMs under an inert argon atmosphere at 1 atm. To test the gas transport properties of CMS-derived POC/MMM, a lab-scale hollow fiber module with two-five fibers was constructed. The results of longer-term operation of synthesized CMS membrane that was continuously operated for 264 h (10 days) with an equimolar binary H2/CO2, CH4/CO2 and C3H6/C3H8 feed at 25°C and 1 bar feed pressure. The modification yielded promising results in the reduction of physical aging of CMS membranes. 

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