Identification of Metal–Organic Framework Materials for Adsorption Separation of Rare Gases: Applicability of Ideal Adsorbed Solution Theory (IAST) and Effects of Inaccessible Framework Regions

Heest, Timothy Van; Teich-McGoldrick, Stephanie; Greathouse, Jeffery A.; Allendorf, Mark D.; Sholl, David S.

doi:10.1021/jp302808j

Cited by 108 publications

(102 citation statements)

References 65 publications

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“…argon, methane), the relationship between pore size and kinetic diameter has already been shown. [18,19,56] By orienting the bond axis parallel to the nanotube, diatomic molecules considered here (N 2 and O 2 ) can access pores much smaller than their kinetic diameters. This finding provides potential new options for gas separation involving diatomic molecules based on very restricted diffusion pathways or pore diameters.…”

Section: Discussionmentioning

confidence: 99%

Molecular simulation of size-selective gas adsorption in idealised carbon nanotubes

Greathouse

Teich-McGoldrick

Allendorf

2015

Molecular Simulation

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Molecular simulations were used to examine the adsorption of diatomic molecules (nitrogen and oxygen) and similarly sized gases (argon and methane) in pores with van der Waals diameters similar in size to the gas diameters. Idealised carbon nanotubes were used to model generic pores, to better understand the effect of pore diameter on guest adsorption in the absence of defects, specific adsorption sites, or variations in pore diameter that often complicate studies of gas adsorption in other porous materials. Molecular dynamics simulations of open nanotubes show that argon and methane are able to enter tubes whose diameters are slightly smaller than the gas diameters. Diatomic gases are able to enter tubes that are significantly smaller than their kinetic diameters with the molecular axis aligned parallel to the nanotube. The results indicate that size-selective adsorption of these gases is theoretically possible, although differences in pore diameters of only a few tenths of an Angstrom are required. Grand canonical Monte Carlo simulations of a 3.38 Å nanotube indicate significant uptake by argon and oxygen, but not nitrogen or methane. The adsorption of nitrogen and methane gradually increases as the nanotube diameter approaches 4.07 Å , and all gases fully saturate a 4.54 Å nanotube. Of the nanotubes studied, the largest adsorption enthalpy for any gas corresponds to the 4.54 Å nanotube, with significantly lower enthalpies seen in the 5.07 Å nanotube. These results suggest an ideal pore diameter for each gas based on the gas-pore van der Waals interaction energies. Trends in the ideal diameter correlate with the minimum tube diameter accessible to each gas.

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Section: Discussionmentioning

confidence: 99%

Molecular simulation of size-selective gas adsorption in idealised carbon nanotubes

Greathouse

Teich-McGoldrick

Allendorf

2015

Molecular Simulation

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“…64 We extend these studies to include PPNs, ZIFs, zeolites, and COFs. With such a rapid increase in the number of materials, the required computational resources will become a bottleneck for these brute-force screening techniques.…”

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confidence: 99%

What Are the Best Materials To Separate a Xenon/Krypton Mixture?

Simon¹,

Mercado²,

et al. 2015

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Accelerating progress in the discovery and deployment of advanced nanoporous materials relies on chemical insight and structure property relationships for rational design. Because of the complexity of this problem, trial-and-error is heavily involved in the laboratory today. A cost-effective route to aid experimental materials discovery is to construct structure models of nanoporous materials in silico and use molecular simulations to rapidly test them and elucidate data-driven guidelines for rational design. For example, highly-tunable nanoporous materials have shown promise as adsorbents for separating an industrially relevant gaseous mixture of xenon and krypton. In this work, we characterize, screen, and analyze the Nanoporous Materials Genome, a database of ca. 670,000 porous material structures, for candidate adsorbents for xenon/krypton separations. For over half a million structures, the computational resources required for a brute-force screening using grand-canonical Monte Carlo simulations of Xe/Kr adsorption are prohibitive.To overcome the computational cost, we used a hybrid approach combining machine learning algorithms (random forests) with molecular simulations. We compared the results from our large-scale screening with simple pore models to rationalize the strong link between pore size and selectivity. With this insight, we then analyzed the anatomy of the binding sites of the most selective materials. These binding sites can be constructed from tubes, pockets, rings, or cages and are often composed of non-discrete chemical fragments. The complexity of these binding sites emphasizes the importance of high-throughput computational screenings to discover new materials. Interestingly, our screening study predicts that the two most selective materials in the database are an aluminophosphate zeolite analogue and a calcium based coordination network, both of which have already been synthesized but not yet tested for Xe/Kr separations.

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“…A more sophisticated approach to convert single gas adsorption data into selectivities is Ideal Adsorbed Solution Theory (IAST) , . IAST computes the spreading pressure on the surface as a function of system pressure for each gas from their adsorption isotherm, from there it computes their adsorbed phase mole fraction at a target system pressure using the fact that spreading pressure for each component is equivalent in the mixture.…”

Section: Resultsmentioning

confidence: 99%

Evaluating the Selectivity of Sorbents for Noble Gas Separations across a Range of Temperatures, Loadings, and Gas Compositions

Lawler

Forster

2016

Zeitschrift anorg allge chemie

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Selectivity is the primary metric for evaluating the effectiveness of a material for the separation of gas mixtures. However, selectivities are difficult to measure experimentally, and, when measured, are typically reported as a single initial selectivity. We have calculated Xe/Kr selectivity as a function of temperature, pressure, and gas composition for HKUST‐1 and six transition metal formates using binary gas grand canonical Monte Carlo (GCMC). Our simulation results agree well with IAST predictions of selectivity from experimental data. We find that selectivity depends strongly on temperature and is best determined at the thermal conditions of the desired process. Additionally, we have shown that improvements in pore volume determination lead to significantly important differences in isotherm prediction that simulated selectivities may be improved by more realistic treatment of this parameter.

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Identification of Metal–Organic Framework Materials for Adsorption Separation of Rare Gases: Applicability of Ideal Adsorbed Solution Theory (IAST) and Effects of Inaccessible Framework Regions

Cited by 108 publications

References 65 publications

Molecular simulation of size-selective gas adsorption in idealised carbon nanotubes

Molecular simulation of size-selective gas adsorption in idealised carbon nanotubes

What Are the Best Materials To Separate a Xenon/Krypton Mixture?

Evaluating the Selectivity of Sorbents for Noble Gas Separations across a Range of Temperatures, Loadings, and Gas Compositions

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