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Self-adjusting binding pockets enhance H2 and CH4 adsorption in a uranium-based metal-organic framework.

ABSTRACT: A new, air-stable, permanently porous uranium(iv) metal-organic framework U(bdc)2 (1, bdc2- = 1,4-benzenedicarboxylate) was synthesized and its H2 and CH4 adsorption properties were investigated. Low temperature adsorption isotherms confirm strong adsorption of both gases in the framework at low pressures. In situ gas-dosed neutron diffraction experiments with different D2 loadings revealed a rare example of cooperative framework contraction (?V = -7.8%), triggered by D2 adsorption at low pressures. This deformation creates two optimized binding pockets for hydrogen (Q st = -8.6 kJ mol-1) per pore, in agreement with H2 adsorption data. Analogous experiments with CD4 (Q st = -24.8 kJ mol-1) and N,N-dimethylformamide as guests revealed that the binding pockets in 1 adjust by selective framework contractions that are unique for each adsorbent, augmenting individual host-guest interactions. Our results suggest that the strategic combination of binding pockets and structural flexibility in metal-organic frameworks holds great potential for the development of new adsorbents with an enhanced substrate affinity.

SUBMITTER: Halter DP

PROVIDER: S-EPMC7473405 | biostudies-literature | 2020 Jul

REPOSITORIES: biostudies-literature

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Self-adjusting binding pockets enhance H2 and CH4 adsorption in a uranium-based metal-organic framework.

Halter Dominik P DP Klein Ryan A RA Boreen Michael A MA Trump Benjamin A BA Brown Craig M CM Long Jeffrey R JR

Chemical science 20200527 26

A new, air-stable, permanently porous uranium(iv) metal-organic framework U(bdc)2 (1, bdc2- = 1,4-benzenedicarboxylate) was synthesized and its H2 and CH4 adsorption properties were investigated. Low temperature adsorption isotherms confirm strong adsorption of both gases in the framework at low pressures. In situ gas-dosed neutron diffraction experiments with different D2 loadings revealed a rare example of cooperative framewo ...[more]

PMID: 32953032

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Project description:Global warming is arguably the biggest scientific challenge of the twenty-first century and its environmental consequences are already noticeable. To mitigate the emissions of greenhouse gases, particularly of CO2, there is an urgent need to design materials with improved adsorbent properties. Five different magnetic ionic liquids were impregnated into the metal-organic framework ZIF-8. The composites were produced by a direct-contact method, and their performance as sorbents for gas separation applications was studied. The impact of the ionic liquid anion on the sorption capacity and ideal CO2/CH4 and CO2/N2 selectivities were studied, focusing on understanding the influence of metal atom and ligand on the adsorbent properties. Reproducible methodology, along with rigorous characterization, were established to assess the impact of the ionic liquid on the performance of the composite materials. Results show that the ionic liquid was well-impregnated, and the ZIF-8 structure was maintained after ionic liquid impregnation. The produced composites were of microporous nature and were thermally stable. CO2, CH4, and N2 adsorption-desorption isotherms were obtained at 303 K and between 0 and 16 bar. The adsorption-desorption data of the composites were compared with that obtained for original ZIF-8. The general trend in composites is that the increased gas uptake per available pore volume compensates the pore volume loss. Adsorption data per unit mass showed that composites have reversible sorption, but inferior gas uptake at all pressure ranges. This is due to the observed total pore volume loss by the ionic liquid pore occupation/blockage. In most cases, composites showed superior selectivity performance at all pressure range. In particular, the composite [C4MIM]2[MnCl4]@ZIF-8 shows a different low-pressure selectivity trend from the original MOF, with a 33% increase in the CO2/N2 selectivity at 1 bar and 19% increase in the CO2/CH4 selectivity at 10 bar. This material shows potential for use in a post-combustion CO2 capture application that can contribute to greenhouse gas mitigation.

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Self-adjusting binding pockets enhance H2 and CH4 adsorption in a uranium-based metal-organic framework.

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Self-adjusting binding pockets enhance H<sub>2</sub> and CH<sub>4</sub> adsorption in a uranium-based metal-organic framework.

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