In Situ Nuclear Magnetic Resonance Investigation of Molecular Adsorption and Kinetics in Metal–Organic Framework UiO-66

An, Yao; Kleinhammes, Alfred; Doyle, Patrick S.; Chen, Enyi; Song, Yan; Morris, Amanda J.; Gibbons, Bradley; Cai, Meng; Johnson, J. Karl; Shukla, Priyanka B.; Vo, Minh Nguyen; Wei, Xin; Wilmer, Christopher E.; Ruffley, Jonathan P.; Huang, Liangliang; Tovar, Trenton M.; Mahle, John J.; Karwacki, Christopher J.; Wu, Yue

doi:10.1021/acs.jpclett.0c03504

Cited by 12 publications

(30 citation statements)

References 36 publications

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“…The IPA adsorption isotherms in pristine and defective UiO-66 were conducted via the in situ NMRdetective systems. 31 As shown in Figure 2, the simulation results agree well with the NMR measurements, which further validates the model and the force field parameters utilized in this work. The results in Figure 2 also show that the saturation adsorptions in pristine UiO-66 and UiO-66 with one missing link and two missing links, are respectively 20, 22, and 24 IPA molecules per unit cell and that IPA adsorption increases when there are more linkers removed from the pristine UiO-66.…”

Section: Models and Simulation Detailssupporting

confidence: 80%

“…A cutoff of 12 Å was applied to all LJ interactions, and the long-range electrostatic interactions were treated by the Ewald summation method. The IPA adsorption isotherms in pristine and defective UiO-66 were conducted via the in situ NMR-detective systems . As shown in Figure , the simulation results agree well with the NMR measurements, which further validates the model and the force field parameters utilized in this work.…”

Section: Models and Simulation Detailssupporting

confidence: 71%

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A Computational Study of Isopropyl Alcohol Adsorption and Diffusion in UiO-66 Metal–Organic Framework: The Role of Missing Linker Defect

Wang

Oliver

et al. 2021

J. Phys. Chem. B

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Defect engineering leads to an effective manipulation of the physical and chemical properties of metal–organic frameworks (MOFs). Taking the common missing linker defect as an example, the defective MOF generally possesses larger pores and a greater surface area/volume ratio, both of which favor an increased amount of adsorption. When it comes to the self-diffusion of adsorbates in MOFs, however, the missing linker is a double-edged sword: the unsaturated metal sites, due to missing linkers, could interact more strongly with adsorbates and result in a slower self-diffusion. Therefore, it is of fundamental importance to evaluate the two competing factors and reveal which one is dominating, a faster self-diffusion due to larger volume or a slower self-diffusion owing to strong interactions at unsaturated sites. In this work, via Monte Carlo and molecular dynamics simulations, we investigate the behavior of isopropyl alcohol (IPA) in the Zr-based UiO-66 MOFs, with a specific focus on the missing linker effects. The results reveal that unsaturated Zr sites bind strongly with IPA molecules, which in return would significantly reduce the self-diffusion coefficient of IPA. Besides this, for the same level of missing linkers, the location of defective sites also makes a difference. We expect such a theoretical study will provide an in-depth understanding of self-diffusion under confinement, inspire better defect engineering strategics, and promote MOF based materials toward challenging real-life applications.

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Section: Models and Simulation Detailssupporting

confidence: 80%

Section: Models and Simulation Detailssupporting

confidence: 71%

A Computational Study of Isopropyl Alcohol Adsorption and Diffusion in UiO-66 Metal–Organic Framework: The Role of Missing Linker Defect

Wang

Oliver

et al. 2021

J. Phys. Chem. B

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“…Effect of Flexibility on the Adsorption of IPA in UiO-66. An et al studied the uptake of IPA from solid-state NMR and gravimetric adsorption isotherms in UiO-66 at 291 K. 65 They compared simulated isotherms for IPA using rigid models of pristine, 8 and 17% missing linker defect UiO-66 having formate capping groups with the experiments. They found that the saturation loading from simulations of 17% defective MOF was in best agreement with the experiments (Figure S14 in ref 65).…”

Section: ■ Results and Discussionmentioning

confidence: 99%

“…For IPA adsorption isotherms, GCMC simulations were performed at 291 K using snapshots for empty flexible UiO-66, seven IPA molecules/fu, and seven acetone molecules/ fu flexible UiO-66 structures at 298 K. The IPA isotherm was computed at 291 K to match the experiments. 65 The small difference in temperature between the MD snapshots (298 K) and GCMC simulations (291 K) should have a negligible impact on the results. The GCMC simulations on the 10 snapshots for each condition were averaged to obtain an estimation of the isotherm including the effects of framework flexibility, both for empty and for adsorbate-loaded configurations.…”

Section: ■ Introductionmentioning

confidence: 98%

Impact of Loading-Dependent Intrinsic Framework Flexibility on Adsorption in UiO-66

Shukla

Johnson

2022

J. Phys. Chem. C

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The vast majority of molecular simulations of adsorption in porous materials make use of the assumption that the framework of the porous material may be held rigid without significantly impacting the accuracy of the computed adsorption isotherm. One reason for this approximation is that explicit inclusion of framework flexibility in adsorption simulations dramatically increases the computational cost of the simulation. Approximate methods for including framework flexibility have been developed that are computationally efficient and have been applied to adsorption of gases in metal–organic frameworks (MOFs) by generating an ensemble of snapshots from a molecular dynamics calculation of an empty MOF and employing these snapshots to generate an isotherm averaged over all the snapshots, holding each snapshot rigid during the adsorption calculation. This method assumes that the adsorbate has negligible impact on the dynamic configurations of the MOF. We demonstrate an efficient method for including adsorbate-induced changes to the MOF framework and show that this assumption is not always valid. Specifically, for acetone and isopropyl alcohol adsorbed in UiO-66, the saturation loading and degree of hydrogen bonding with the framework significantly increased through the inclusion of adsorbate-induced framework flexibility. We show that adsorption simulations that include adsorbate-induced flexibility match the experimental data for these systems much better than simulations using either the rigid approximation or including the framework flexibility of the empty MOF. We expect that adsorbate-induced flexibility may be important for adsorption in many similar systems.

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“…Early studies used electromagnets to study NMR relaxation as a function of temperature. − Modern day high-field NMR spectroscopy can offer a much more detailed picture, down to the atomic scale, by directly probing the adsorbed phase in terms of structure and dynamics. To date, however, mainly single-point adsorption high-field NMR experiments have been performed, since full isotherm measurements are nontrivial to implement on superconducting NMR instruments, − or otherwise deviate from the ideal conditions set as industry standards for isotherm acquisition (e.g., using gravimetric techniques, imaging, etc. ). , Recent studies have attempted to circumvent these limitations with the use of low-field NMR for the study of sorbent materials.…”

Section: Single-pore Mof: Zif-8mentioning

confidence: 99%

Benchtop In Situ Measurement of Full Adsorption Isotherms by NMR

et al. 2021

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Physisorption using gas or vapor probe molecules is the most common characterization technique for porous materials. The method provides textural information on the adsorbent as well as the affinity for a specific adsorbate, typically through equilibrium pressure measurements. Here, we demonstrate how low-field NMR can be used to measure full adsorption isotherms, and how by selectively measuring 1H spins of the adsorbed probe molecules, rather than those in the vapor phase, this “NMR-relaxorption” technique provides insights about local dynamics beyond what can be learned from physisorption alone. The potential of this double-barreled approach was illustrated for a set of microporous metal–organic frameworks (MOFs). For methanol adsorption in ZIF-8, the method identifies multiple guest molecules populations assigned to MeOH clusters in the pore center, MeOH bound at cage windows and to MeOH adsorption on defect sites. For UiO-66(Zr), the sequential pore filling is demonstrated and accurate pore topologies are directly obtained, and for MIL-53(Al), structural phase transitions are accurately detected and linked with two populations of dimeric chemical species localized to specific positions in the framework.

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In Situ Nuclear Magnetic Resonance Investigation of Molecular Adsorption and Kinetics in Metal–Organic Framework UiO-66

Cited by 12 publications

References 36 publications

A Computational Study of Isopropyl Alcohol Adsorption and Diffusion in UiO-66 Metal–Organic Framework: The Role of Missing Linker Defect

A Computational Study of Isopropyl Alcohol Adsorption and Diffusion in UiO-66 Metal–Organic Framework: The Role of Missing Linker Defect

Impact of Loading-Dependent Intrinsic Framework Flexibility on Adsorption in UiO-66

Benchtop In Situ Measurement of Full Adsorption Isotherms by NMR

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