J. Wieme

Unfolding the terahertz spectrum of soft porous crystals: rigid unit modes and their impact on phase transitions

A.E.J. Hoffman, I. Senkovska, J. Wieme, A. Krylov, S. Kaskel, V. Van Speybroeck
Journal of Materials Chemistry A
10 (33), 17254-17266
2022
A1

Abstract 

Phase transitions in exible metal-organic frameworks or soft porous crystals are mediated by low-frequency phonons or rigid-unit modes. The alteration of specic building blocks may change the lattice dynamics of these frameworks, which can inuence the phase transition mechanism. In this work, the impact of building block substitution on the rigid-unit modes in exible MIL-53 analogs with a winerack topology will be investigated via ab initio lattice dynamics calculations. First, the accuracy of the theoretical simulations is veried via experimental Raman measurements, which provide unique ngerprint vibrations in the terahertz range to characterize the phase transition. Following analysis of the low-frequency vibrations shows that there exists a set of universal rigid-unit modes inducing translations and/or rotations of the building blocks. The theoretical results demonstrate that linker substitutions have a large eect on the rigid-unit mode frequencies, whereas this is less so for inorganic chain substitutions. These ndings may help to rationally tune the phonon frequencies in soft porous crystals.

Gold Open Access

DOI 

http://dx.doi.org/10.1039/d2ta01678h

Crystals springing into action: metal-organic framework CUK-1 as a pressure-driven molecular spring dagger

P. Iacomi, J.S. Lee, L. Vanduyfhuys, K. H. Cho, P. Fertey, J. Wieme, D. Granier, G. Maurin, V. Van Speybroeck, J.-S. Chang, P.G. Yot
Chemical Science
12, 5682-5687
2021
A1

Abstract 

Mercury porosimetry and in situ high pressure single crystal X-ray diffraction revealed the wine-rack CUK-1 MOF as a unique crystalline material capable of a fully reversible mechanical pressure-triggered structural contraction. The near-absence of hysteresis upon cycling exhibited by this robust MOF, akin to an ideal molecular spring, is associated with a constant work energy storage capacity of 40 J/gr. Molecular simulations were further deployed to uncover the free-energy landscape behind this unprecedented pressure-responsive phenomenon in the area of compliant hybrid porous materials. This discovery is of utmost importance from the perspective of instant energy storage and delivery.

Open Access version available at UGent repository
Green Open Access

DOI 

http://dx.doi.org/10.1039/D1SC00205H

High-rate nanofluidic energy absorption in porous zeolitic frameworks

Y. Sun, S.M.J. Rogge, A. Lamaire, S. Vandenbrande, J. Wieme, C.R. Siviour, V. Van Speybroeck, J.-C. Tan
Nature Materials
20 (7), 1015–1023
2021
A1

Abstract 

Optimal mechanical impact absorbers are reusable and exhibit high specific energy absorption. The forced intrusion of liquid water in hydrophobic nanoporous materials, such as zeolitic imidazolate frameworks (ZIFs), presents an attractive pathway to engineer such systems. However, to harness their full potential, it is crucial to understand the underlying water intrusion and extrusion mechanisms under realistic, high-rate deformation conditions. Here, we report a critical increase of the energy absorption capacity of confined water-ZIF systems at elevated strain rates. Starting from ZIF-8 as proof-of-concept, we demonstrate that this attractive rate dependence is generally applicable to cage-type ZIFs but disappears for channel-containing zeolites. Molecular simulations reveal that this phenomenon originates from the intrinsic nanosecond timescale needed for critical-sized water clusters to nucleate inside the nanocages, expediting water transport through the framework. Harnessing this fundamental understanding, design rules are formulated to construct effective, tailorable and reusable impact energy absorbers for challenging new applications.

DOI 

http://dx.doi.org/10.1038/s41563-021-00977-6

Correlating MOF-808 parameters with mixed-matrix membrane (MMM) CO2 permeation for a more rational MMM development

R. Thür, D. Van Havere, N. Van Velthoven, S. Smolders, A. Lamaire, J. Wieme, V. Van Speybroeck, D. De Vos, I. Vankelecom
Journal of Materials Chemistry A
9 (21), 12782-12796
2021
A1

Abstract 

Consistent structure-performance relationships for the design of MOF (metal-organic framework)-based mixed-matrix membranes (MMMs) for gas separation are currently scarce in MMM literature. An important step in establishing such relationships could be to correlate intrinsic MOF parameters, such as CO2 uptake and the CO2 adsorption enthalpy (Qst), with the separation performance indicators of the MMM (i.e. separation factor and permeability). Such a study presumes the availability of a platform MOF, which allows systematic comparison of the relevant MOF parameters. MOF-808 can take up the role of such platform MOF, owing to its unique cluster coordination and subsequent ease of introducing additional functional molecules. For this purpose, formic acid (FA) modulated MOF-808 (MOF-FA) was post-synthetically functionalized with five different ligands (histidine (His), benzoic acid (BA), glycolic acid (GA), lithium sulfate (Li2SO4) and trifluoroacetic acid (TFA)) to create a series of isostructural MOFs with varying affinity/diffusivity properties but as constant as possible remaining properties (e.g. particles size distribution). CO2 uptake and CO2 adsorption enthalpy of the MOFs were determined with CO2 sorption experiments and Clausius-Clapeyron analysis. These MOF properties were subsequently linked to the CO2/N2 separation factor and CO2 permeability of the corresponding MMM. Unlike what is often assumed in literature, MOF-808 CO2 uptake proved to be a poor indicator for MMM performance. In contrast, a strong correlation was observed between Qst at high CO2 loadings on one hand and CO2 permeability under varying feed conditions on the other hand. Furthermore, correlation coefficients of Qst,15 and Qst,30 (Qst at 15 and 30 cm3 (STP)/g) with the separation factor were significantly better than those calculated for CO2 uptake. The surprising lack of correlation between membrane performance and CO2 uptake and the strong correlation with Qst opens possibilities to rationally design MMMs and stresses the need for more fundamental research focused on finding consistent relationships between filler properties and the final membrane performance.

DOI 

http://dx.doi.org/10.1039/D0TA10207E

Chlorination of a Zeolitic-Imidazolate Framework Tunes Packing and van der Waals Interaction of Carbon Dioxide for Optimized Adsorptive Separation

L.H. Wee, S. Vandenbrande, S.M.J. Rogge, J. Wieme, K. Asselman, E. Jardim, J. Silvestre-Albero, J. Navarro, V. Van Speybroeck, J.A. Martens, C. Kirschhock
JACS (Journal of the American Chemical Society)
143 (13), 4962-4968
2021
A1

Abstract 

Molecular separation of carbon dioxide (CO2) and methane (CH4) is of growing interest for biogas upgrading, carbon capture and utilization, methane synthesis and for purification of natural gas. Here, we report a new zeolitic-imidazolate framework (ZIF), coined COK-17, with exceptionally high affinity for the adsorption of CO2 by London dispersion forces, mediated by chlorine substituents of the imidazolate linkers. COK-17 is a new type of flexible zeolitic-imidazolate framework Zn(4,5-dichloroimidazolate)2 with the SOD framework topology. Below 200 K it displays a metastable closed-pore phase next to its stable open-pore phase. At temperatures above 200 K, COK-17 always adopts its open-pore structure, providing unique adsorption sites for selective CO2 adsorption and packing through van der Waals interactions with the chlorine groups, lining the walls of the micropores. Localization of the adsorbed CO2 molecules by Rietveld refinement of X-ray diffraction data and periodic density functional theory calculations revealed the presence and nature of different adsorption sites. In agreement with experimental data, grand canonical Monte Carlo simulations of adsorption isotherms of CO2 and CH4 in COK-17 confirmed the role of the chlorine functions of the linkers and demonstrated the superiority of COK-17 compared to other adsorbents such as ZIF-8 and ZIF-71.

Gold Open Access

DOI 

http://dx.doi.org/10.1021/jacs.0c08942

Unravelling thermal stress due to thermal expansion mismatch in metal-organic frameworks for methane storage

J. Wieme, V. Van Speybroeck
Journal of Materials Chemistry A
11 (8), 4898-4906
2021
A1

Abstract 

Thermal stress is present in all systems undergoing temperature changes during their operation. Metal-organic frameworks (MOFs) are a class of porous, crystalline materials ideally suited for a wide range of adsorption-based technologies. The release and consumption of the heat of adsorption instigate temperature fluctuations and thermal stress in these materials that could induce disruptive volume changes. To bring these materials to engineering applications, it is of utmost importance to understand their thermal expansion behavior and the overall induced thermal stress due to thermal expansion mismatch with other components. In this work, we focus on a large group of MOFs known to have promising methane adsorption properties and predict their thermal expansion coefficients based on force field molecular dynamics simulations. Negative thermal expansion (NTE) behavior is predicted for all studied MOFs, and the magnitude of the NTE coefficients is found to be positively correlated with the degree of porosity of the frameworks. Finally, as a proxy for the thermal stress, the thermal pressure coefficient is calculated, which is found to be in the range between polymers and ceramics. Variations within the operating temperature range of MOFs are therefore expected to result in a relatively low thermal stress.

DOI 

http://dx.doi.org/10.1039/D0TA09462E

Atomistic insight in the flexibility and heat transport properties of the stimuli-responsive metal-organic framework MIL-53(Al) for water-adsorption applications using molecular simulations

A. Lamaire, J. Wieme, A.E.J. Hoffman, V. Van Speybroeck
Faraday Discussions
225, 301-323
2021
A1

Abstract 

To exploit the full potential of metal-organic frameworks as solid adsorbents in water-adsorption applications, many challenges remain to be solved. A more fundamental insight into the properties of the host material and the influence water exerts on them can be obtained by performing molecular simulations. In this work, the prototypical flexible MIL-53(Al) framework is modelled using advanced molecular dynamics simulations. For different water loadings, the presence of water is shown to affect the relative stability of MIL-53(Al), triggering a phase transition from the narrow-pore to the large-pore phase at the highest considered loading. Furthermore, the effect of confinement on the structural organisation of the water molecules is also examined for different pore volumes of MIL-53(Al). For the framework itself, we focus on the thermal conductivity, as this property plays a decisive role in the efficiency of adsorption-based technologies, due to the energy-intensive adsorption and desorption cycles. To this end, the heat transfer characteristics of both phases of MIL-53(Al) are studied, demonstrating a strong directional dependence for the thermal conductivity.

Gold Open Access

DOI 

http://dx.doi.org/10.1039/D0FD00025F

Thermal Engineering of Metal-Organic Frameworks for Adsorption Applications: A Molecular Simulations Perspective

J. Wieme, S. Vandenbrande, A. Lamaire, V. Kapil, L. Vanduyfhuys, V. Van Speybroeck
ACS Applied Materials & Interfaces
11 (42), 38697-38707
2019
A1

Abstract 

Thermal engineering of metal-organic frameworks (MOFs) for adsorption-based applications is very topical in view of their industrial potential, especially since heat management and thermal stability have been identified as important obstacles. Hence, a fundamental understanding of the structural and chemical features underpinning their intrinsic thermal properties is highly sought-after. Herein, we investigate the nanoscale behavior of a diverse set of frameworks using molecular simulation techniques and critically compare properties such as thermal conductivity, heat capacity and thermal expansion with other material classes. Furthermore, we propose a hypothetical thermodynamic cycle to estimate the temperature rise associated with adsorption for the most important greenhouse and energy-related gases (CO2 and CH4). This macroscopic response on the heat of adsorption connects the intrinsic thermal properties with the adsorption properties, and allows us to evaluate their importance.

DOI 

http://dx.doi.org/10.1021/acsami.9b12533

Pillared-layered metal-organic frameworks for mechanical energy storage applications

J. Wieme, S.M.J. Rogge, P.G. Yot, L. Vanduyfhuys, S.-K. Lee, J.-S. Chang, M. Waroquier, G. Maurin, V. Van Speybroeck
Journal of Materials Chemistry A
7 (39), 22663-22674
2019
A1

Abstract 

Herein we explore the unique potential of pillared-layered metal–organic frameworks of the DMOF-1 family for mechanical energy storage applications. In this work, we theoretically predict for the guest-free DMOF-1 a new contracted phase by exerting an external mechanical pressure of more than 200 MPa with respect to the stable phase at atmospheric pressure. The breathing transition is accompanied by a very large volume contraction of about 40%. The high transition pressures and associated volume changes make these materials highly promising with an outstanding mechanical energy work. Furthermore, we show that changing the nature of the metal allows to tune the behavior under mechanical pressure. The various phases were revealed by a combination of periodic density-functional theory calculations, force field molecular dynamics simulations and mercury intrusion experiments for DMOF-1(Zn) and DMOF-1(Cu). The combined experimental and theoretical approach allowed to discover the potential of these materials for new technological developments.

Gold Open Access

DOI 

http://dx.doi.org/10.1039/C9TA01586H

Structure–Mechanical Stability Relations of Metal-Organic Frameworks via Machine Learning

P.Z. Moghadam, S.M.J. Rogge, A. Li, C.-M. Chow, J. Wieme, N. Moharrami, M. Aragones-Anglada, G. Conduit, D.A. Gomez-Gualdron, V. Van Speybroeck, D. Fairen-Jimenez
Matter
1 (1), 219-234
2019
A1

Abstract 

Assessing the mechanical stability of metal-organic frameworks (MOFs) is critical to bring these materials to any application. Here, we derive the first interactive map of the structure-mechanical landscape of MOFs by performing a multi-level computational analysis. First, we used high-throughput molecular simulations for 3,385 MOFs containing 41 distinct network topologies. Second, we developed a freely available machine-learning algorithm to automatically predict the mechanical properties of MOFs. For distinct regions of the high-throughput space, in-depth analysis based on in operando molecular dynamics simulations reveals the loss-of-crystallinity pressure within a given topology. The overarching mechanical screening approach presented here reveals the sensitivity on structural parameters such as topology, coordination characteristics and the nature of the building blocks, and paves the way for computational as well as experimental researchers to assess and design MOFs with enhanced mechanical stability to accelerate the translation of MOFs to industrial applications.

Gold Open Access

DOI 

http://dx.doi.org/10.1016/j.matt.2019.03.002

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