ORCID Profile
0000-0001-9504-8514
Current Organisations
University of Groningen
,
Max Planck Institute for Solid State Research
,
Technische Universität Dresden
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Publisher: American Chemical Society (ACS)
Date: 18-01-2021
DOI: 10.26434/CHEMRXIV.13562813
Abstract: New nanoporous materials are able to revolutionize adsorption and separation processes. In particular, materials with adaptive cavities have high selectivity and may display previously undiscovered phenomena, such as negative gas adsorption (NGA), in which gas is released from the framework upon an increase in pressure. Although the thermodynamic driving force behind this and many other counterintuitive adsorption phenomena have been thoroughly investigated in recent years, several experimental observations remain difficult to explain. This necessitates a comprehensive analysis of gas adsorption akin to the conformational free energy landscapes used to understand the function of proteins. For the first time, we constructed the complete thermodynamic landscape of methane adsorption on DUT-49, a system that demonstrates NGA. Traversing this complex landscape correctly reproduces the experimentally observed structural transitions, the temperature dependence of the NGA phenomenon and the observed hysteresis between adsorption and desorption. The complete thermodynamic description presented here provides unparalleled insight into the process of adsorption and provides a framework to understand other adsorbents that challenge our preconceptions. br /
Publisher: American Chemical Society (ACS)
Date: 26-11-2020
DOI: 10.26434/CHEMRXIV.13286009
Abstract: Although light is a prominent stimulus for smart materials, the application of photoswitches as light-responsive triggers for phase transitions of porous materials remains poorly explored. Here we incorporate an azobenzene photoswitch in the backbone of a metal-organic framework producing light-induced structural contraction of the porous network in parallel to gas adsorption. Light-stimulation enables non-invasive spatiotemporal control over the mechanical properties of the framework, which ultimately leads to pore contraction and subsequent guest release via negative gas adsorption. The complex mechanism of light-gated breathing is established by a series of in situ diffraction and spectroscopic experiments, supported by quantum mechanical and molecular dynamic simulations. Unexpectedly, this study identifies a novel light-induced deformation mechanism of constrained azobenzene photoswitches relevant to the future design of light-responsive materials.
Publisher: American Chemical Society (ACS)
Date: 27-01-2020
DOI: 10.26434/CHEMRXIV.11708844
Abstract: Molecules in gas and liquid states, as well as in solution, exhibit significant and random Brownian motion. Molecules in the solid-state, although strongly immobilized, can still exhibit significant intramolecular dynamics. However, in most framework materials, these intramolecular dynamics are driven by temperature, and therefore are neither controlled nor spatially or temporarily aligned. In recent years, several ex les of molecular machines that allow for a stimuli-responsive control of dynamical motion, such as rotation, have been reported. / br / In this contribution, we investigate the local and global properties of a Lennard-Jones (LJ) fluid surrounding a molecular motor and consider the influence of cooperative and non-directional rotation for a molecular motor-containing pore system. This study uses classical molecular dynamics simulations to describe a minimal model, which was developed to resemble known molecular motors. The properties of an LJ liquid surrounding an isolated molecular mo-tor remain mostly unaffected by the introduced rotation. We then considered an arrangement of motors within a one-dimensional pore. Changes in diffusivity for pore sizes approaching the length of the rotor were observed, resulting from rotation of the motors. We also considered the influence of cooperative motor directionality on the directional transport properties of this con-fined fluid. Importantly, we discovered that specific unidirectional rotation of altitudinal motors can produce directed diffusion. / br / This study provides an essential insight into molecular machine-containing frameworks, highlighting the specific structural arrangements that can produce directional mass transport. /
Publisher: Frontiers Media SA
Date: 07-01-2022
Publisher: American Chemical Society (ACS)
Date: 28-01-2020
DOI: 10.26434/CHEMRXIV.11733408
Abstract: In this contribution, we present an extensive investigation of adsorption of a range of different gases at various temperatures in DUT-49, a metal-organic framework which features a negative gas adsorption (NGA) transition. Adsorption experiments at temperatures ranging from 21 to 308 K, were used to identify, for each guest, a critical temperature range in which NGA occurs. The experimental results were complemented by molecular simulations that rationalize the absence of NGA at elevated temperatures and the non-monotonic behavior observed upon temperature decrease.
Publisher: American Chemical Society (ACS)
Date: 18-03-2019
DOI: 10.26434/CHEMRXIV.7527680.V2
Abstract: We describe a general model to explore responsive adsorption processes in flexible porous materials.This model combines mean field formalism of the osmotic potential, classical density functional theory of adsorption in slit pore models and generic potential functions which represent the Helmholtz free energy landscape of a porous system.Using this model, we focus on recreating flexible adsorption phenomena observed in prototypical metal-organic frameworks, especially the recently discovered effect of negative gas adsorption (NGA).We identify the key characteristics required for the model to generate unusual adsorption processes and subsequently employ an extensive parametric study to outline conditions under which gate-opening and NGA are observed.This powerful approach will guide the design of responsive porous materials and the discovery of entirely new adsorption processes.
Publisher: American Chemical Society (ACS)
Date: 08-07-2020
DOI: 10.26434/CHEMRXIV.12619064
Abstract: Framework materials at the molecular level, such as metal-organic frameworks (MOF), were recently found to exhibit exotic and counterintuitive micromechanical properties. Stimulated by host-guest interactions, these so-called soft porous crystals can display counterintuitive adsorption phenomena such as negative gas adsorption (NGA). NGA materials are bistable frameworks where the occurrence of a metastable overloaded state leads to pressure lification upon a sudden framework contraction. How can we control activation barriers and energetics via functionalization of the molecular building blocks that dictate the frameworks’ 30 mechanical response? In this work we tune the elastic and inelastic properties of building blocks at the 31 molecular level and analyze the mechanical response of the resulting frameworks. From a set of 11 frameworks, we demonstrate that widening of the backbone increases elasticity, while elongation of the building blocks results in a decrease in critical yield stress of buckling. We further functionalize the backbone by incorporation of sp3 hybridized carbon atoms to soften the molecular building blocks, or stiffen them with sp2 and sp carbons. Computational modeling shows how these modifications of the building blocks tune the 36 activation barriers within the energy landscape of the guest-free bistable frameworks. Only frameworks with free energy barriers in the range of 800 to 1100 kJ mol–1 37 per unit cell, and moderate yield stress of 0.6 to 38 1.2 nN for single ligand buckling, exhibit adsorption-induced contraction and negative gas adsorption. Advanced experimental in situ methodologies give detailed insights into the structural transitions and the adsorption behavior. The new framework DUT-160 shows the highest magnitude of NGA ever observed for nitrogen adsorption at 77 K. Our computational and experimental analysis of the energetics and mechanical response functions of porous frameworks is an important step towards tuning activation barriers in dynamic framework materials and provides critical design principles for molecular building blocks leading to pressure lifying materials br
Publisher: Royal Society of Chemistry (RSC)
Date: 2021
DOI: 10.1039/D0FD90036B
Publisher: Springer Science and Business Media LLC
Date: 03-06-2023
DOI: 10.1038/S41467-023-38737-6
Abstract: A unique feature of metal-organic frameworks (MOFs) in contrast to rigid nanoporous materials is their structural switchabilty offering a wide range of functionality for sustainable energy storage, separation and sensing applications. This has initiated a series of experimental and theoretical studies predominantly aiming at understanding the thermodynamic conditions to transform and release gas, but the nature of sorption-induced switching transitions remains poorly understood. Here we report experimental evidence for fluid metastability and history-dependent states during sorption triggering the structural change of the framework and leading to the counterintuitive phenomenon of negative gas adsorption (NGA) in flexible MOFs. Preparation of two isoreticular MOFs differing by structural flexibility and performing direct in situ diffusion studies aided by in situ X-ray diffraction, scanning electron microscopy and computational modelling, allowed assessment of n -butane molecular dynamics, phase state, and the framework response to obtain a microscopic picture for each step of the sorption process.
Publisher: Royal Society of Chemistry (RSC)
Date: 2021
DOI: 10.1039/D0FD90034F
Publisher: American Chemical Society (ACS)
Date: 13-03-2019
DOI: 10.26434/CHEMRXIV.7796543
Abstract: Critical design criteria for negative gas adsorption (NGA), a counterintuitive feature of pressure lifying materials, hitherto uniquely observed in a highly porous framework compound (DUT-49), are derived by analysing the physical effects of micromechanics, pore size, interpenetration, adsorption enthalpies, and the pore filling mechanism using advanced in situ X-ray and neutron diffraction, NMR spectroscopy, and calorimetric techniques parallelized to adsorption for a series of six isoreticular networks. Aided by computational modelling, we identify DUT-50 as a new pressure lifying material featuring distinct NGA transitions upon methane and argon adsorption. In situ neutron diffraction analysis of the methane (CD4) adsorption sites at 111 K supported by grand canonical Monte Carlo simulations reveals a sudden population of the largest mesopore to be the critical filling step initiating structural contraction and NGA. In contrast, interpenetration leads to framework stiffening and specific pore volume reduction, both factors effectively suppressing NGA transitions.
Publisher: Frontiers Media SA
Date: 11-11-2021
DOI: 10.3389/FCHEM.2021.772059
Abstract: Miniaturization is a key aspect of materials science. Owing to the increase in quality experimental and computational tools available to researchers, it has become clear that the crystal size and morphology of porous framework materials, including metal-organic frameworks and covalent organic frameworks, play a vital role in defining the physicochemical behaviour of these materials. However, given the multiscale and multidisciplinary challenges associated with establishing how crystal size and morphology affect the structure and behaviour of a material–from local to global structural modifications and from static to dynamic effects–a comprehensive mechanistic understanding of size and morphology effects is missing. Herein, we provide our perspective on the current state-of-the-art of this topic, drawn from various complementary disciplines. From a fundamental point of view, we discuss how controlling the crystal size and morphology can alter the mechanical and adsorption properties of porous framework materials and how this can impact phase stability. Special attention is also given to the quest to develop new computational tools capable of modelling these multiscale effects. From a more applied point of view, given the recent progress in this research field, we highlight the importance of crystal size and morphology control in drug delivery. Moreover, we provide an outlook on how to advance each discussed field by size and morphology control, which would open new design opportunities for functional porous framework materials.
Publisher: American Chemical Society (ACS)
Date: 26-11-2020
DOI: 10.26434/CHEMRXIV.13286009.V1
Abstract: Although light is a prominent stimulus for smart materials, the application of photoswitches as light-responsive triggers for phase transitions of porous materials remains poorly explored. Here we incorporate an azobenzene photoswitch in the backbone of a metal-organic framework producing light-induced structural contraction of the porous network in parallel to gas adsorption. Light-stimulation enables non-invasive spatiotemporal control over the mechanical properties of the framework, which ultimately leads to pore contraction and subsequent guest release via negative gas adsorption. The complex mechanism of light-gated breathing is established by a series of in situ diffraction and spectroscopic experiments, supported by quantum mechanical and molecular dynamic simulations. Unexpectedly, this study identifies a novel light-induced deformation mechanism of constrained azobenzene photoswitches relevant to the future design of light-responsive materials.
Publisher: Royal Society of Chemistry (RSC)
Date: 2021
DOI: 10.1039/D0FD00016G
Abstract: Simulations reveal the influence of rotating molecular motors and the importance of orientation and directionality for altering the transport properties of fluids. This has outlined that motors with specific rotation can generate directed diffusion.
Publisher: American Chemical Society (ACS)
Date: 28-01-2020
DOI: 10.26434/CHEMRXIV.11733408.V1
Abstract: In this contribution, we present an extensive investigation of adsorption of a range of different gases at various temperatures in DUT-49, a metal-organic framework which features a negative gas adsorption (NGA) transition. Adsorption experiments at temperatures ranging from 21 to 308 K, were used to identify, for each guest, a critical temperature range in which NGA occurs. The experimental results were complemented by molecular simulations that rationalize the absence of NGA at elevated temperatures and the non-monotonic behavior observed upon temperature decrease.
Publisher: Royal Society of Chemistry (RSC)
Date: 2020
DOI: 10.1039/D0SC03727C
Abstract: We characterise the elastic properties of molecular building blocks and how they impact the mechanical properties of soft porous crystals.
Publisher: American Chemical Society (ACS)
Date: 27-01-2020
DOI: 10.26434/CHEMRXIV.11708844.V1
Abstract: Molecules in gas and liquid states, as well as in solution, exhibit significant and random Brownian motion. Molecules in the solid-state, although strongly immobilized, can still exhibit significant intramolecular dynamics. However, in most framework materials, these intramolecular dynamics are driven by temperature, and therefore are neither controlled nor spatially or temporarily aligned. In recent years, several ex les of molecular machines that allow for a stimuli-responsive control of dynamical motion, such as rotation, have been reported. In this contribution, we investigate the local and global properties of a Lennard-Jones (LJ) fluid surrounding a molecular motor and consider the influence of cooperative and non-directional rotation for a molecular motor-containing pore system. This study uses classical molecular dynamics simulations to describe a minimal model, which was developed to resemble known molecular motors. The properties of an LJ liquid surrounding an isolated molecular mo-tor remain mostly unaffected by the introduced rotation. We then considered an arrangement of motors within a one-dimensional pore. Changes in diffusivity for pore sizes approaching the length of the rotor were observed, resulting from rotation of the motors. We also considered the influence of cooperative motor directionality on the directional transport properties of this con-fined fluid. Importantly, we discovered that specific unidirectional rotation of altitudinal motors can produce directed diffusion. This study provides an essential insight into molecular machine-containing frameworks, highlighting the specific structural arrangements that can produce directional mass transport.
Publisher: Springer Science and Business Media LLC
Date: 12-08-2019
DOI: 10.1038/S41467-019-11565-3
Abstract: Switchable metal-organic frameworks (MOFs) have been proposed for various energy-related storage and separation applications, but the mechanistic understanding of adsorption-induced switching transitions is still at an early stage. Here we report critical design criteria for negative gas adsorption (NGA), a counterintuitive feature of pressure lifying materials, hitherto uniquely observed in a highly porous framework compound (DUT-49). These criteria are derived by analysing the physical effects of micromechanics, pore size, interpenetration, adsorption enthalpies, and the pore filling mechanism using advanced in situ X-ray and neutron diffraction, NMR spectroscopy, and calorimetric techniques parallelised to adsorption for a series of six isoreticular networks. Aided by computational modelling, we identify DUT-50 as a new pressure lifying material featuring distinct NGA transitions upon methane and argon adsorption. In situ neutron diffraction analysis of the methane (CD 4 ) adsorption sites at 111 K supported by grand canonical Monte Carlo simulations reveals a sudden population of the largest mesopore to be the critical filling step initiating structural contraction and NGA. In contrast, interpenetration leads to framework stiffening and specific pore volume reduction, both factors effectively suppressing NGA transitions.
Publisher: American Chemical Society (ACS)
Date: 25-07-2018
Publisher: Royal Society of Chemistry (RSC)
Date: 2021
DOI: 10.1039/D0FD90033H
Publisher: American Chemical Society (ACS)
Date: 18-01-2021
DOI: 10.26434/CHEMRXIV.13562813.V1
Abstract: New nanoporous materials are able to revolutionize adsorption and separation processes. In particular, materials with adaptive cavities have high selectivity and may display previously undiscovered phenomena, such as negative gas adsorption (NGA), in which gas is released from the framework upon an increase in pressure. Although the thermodynamic driving force behind this and many other counterintuitive adsorption phenomena have been thoroughly investigated in recent years, several experimental observations remain difficult to explain. This necessitates a comprehensive analysis of gas adsorption akin to the conformational free energy landscapes used to understand the function of proteins. For the first time, we constructed the complete thermodynamic landscape of methane adsorption on DUT-49, a system that demonstrates NGA. Traversing this complex landscape correctly reproduces the experimentally observed structural transitions, the temperature dependence of the NGA phenomenon and the observed hysteresis between adsorption and desorption. The complete thermodynamic description presented here provides unparalleled insight into the process of adsorption and provides a framework to understand other adsorbents that challenge our preconceptions.
Publisher: American Chemical Society (ACS)
Date: 31-12-2018
DOI: 10.26434/CHEMRXIV.7527680.V1
Abstract: We describe a general model to explore responsive adsorption processes in flexible porous materials.This model combines mean field formalism of the osmotic potential, classical density functional theory of adsorption in slit pore models and generic potential functions which represent the Helmholtz free energy landscape of a porous system.Using this model, we focus on recreating flexible adsorption phenomena observed in prototypical metal-organic frameworks, especially the recently discovered effect of negative gas adsorption (NGA).We identify the key characteristics required for the model to generate unusual adsorption processes and subsequently employ an extensive parametric study to outline conditions under which gate-opening and NGA are observed.This powerful approach will guide the design of responsive porous materials and the discovery of entirely new adsorption processes.
Publisher: American Chemical Society (ACS)
Date: 15-03-2021
DOI: 10.1021/JACS.1C00522
Publisher: American Chemical Society (ACS)
Date: 13-03-2019
DOI: 10.26434/CHEMRXIV.7796543.V1
Abstract: Critical design criteria for negative gas adsorption (NGA), a counterintuitive feature of pressure lifying materials, hitherto uniquely observed in a highly porous framework compound (DUT-49), are derived by analysing the physical effects of micromechanics, pore size, interpenetration, adsorption enthalpies, and the pore filling mechanism using advanced in situ X-ray and neutron diffraction, NMR spectroscopy, and calorimetric techniques parallelized to adsorption for a series of six isoreticular networks. Aided by computational modelling, we identify DUT-50 as a new pressure lifying material featuring distinct NGA transitions upon methane and argon adsorption. In situ neutron diffraction analysis of the methane (CD4) adsorption sites at 111 K supported by grand canonical Monte Carlo simulations reveals a sudden population of the largest mesopore to be the critical filling step initiating structural contraction and NGA. In contrast, interpenetration leads to framework stiffening and specific pore volume reduction, both factors effectively suppressing NGA transitions.
Publisher: Royal Society of Chemistry (RSC)
Date: 2019
DOI: 10.1039/C9SC01299K
Abstract: A general thermodynamic model to investigate responsive adsorption processes in flexible porous materials.
Publisher: Springer Science and Business Media LLC
Date: 12-04-2022
DOI: 10.1038/S41467-022-29149-Z
Abstract: Although light is a prominent stimulus for smart materials, the application of photoswitches as light-responsive triggers for phase transitions of porous materials remains poorly explored. Here we incorporate an azobenzene photoswitch in the backbone of a metal-organic framework producing light-induced structural contraction of the porous network in parallel to gas adsorption. Light-stimulation enables non-invasive spatiotemporal control over the mechanical properties of the framework, which ultimately leads to pore contraction and subsequent guest release via negative gas adsorption. The complex mechanism of light-gated breathing is established by a series of in situ diffraction and spectroscopic experiments, supported by quantum mechanical and molecular dynamic simulations. Unexpectedly, this study identifies a novel light-induced deformation mechanism of constrained azobenzene photoswitches relevant to the future design of light-responsive materials.
Publisher: American Chemical Society (ACS)
Date: 08-03-2018
DOI: 10.26434/CHEMRXIV.5962240.V1
Abstract: In this article we report the synthesis and detailed analysis of the highly porous metal-organic framework DUT-48, isoreticular to DUT-49 a material which shows an adsorption-induced structural transition. DUT-48 has impressive porosity and methane storage capacity, however displays conventional adsorption behaviour. The contrasting flexibility of DUT-48 and DUT-49 were analysed and rationalised using a combination of novel experimental and computational techniques. Microcalorimetry measurements, in conjunction with molecular simulations, demonstrate that DUT-48 has a significantly lower adsorption enthalpy difference and a higher framework stiffness which leads to an absence of adsorption-induced transitions and negative gas adsorption (NGA). However, by analysing the mechanical behaviour of both DUT-48 and DUT-49, employing mercury porosimetry experiments, we discovered that both materials exhibit large volume changes under hydrostatic compression, demonstrating noteworthy potential as shock absorbers, and directly linking internal adsorption-induced contraction to external hydrostatic compression.
Publisher: American Chemical Society (ACS)
Date: 08-07-2020
DOI: 10.26434/CHEMRXIV.12619064.V1
Abstract: Framework materials at the molecular level, such as metal-organic frameworks (MOF), were recently found to exhibit exotic and counterintuitive micromechanical properties. Stimulated by host-guest interactions, these so-called soft porous crystals can display counterintuitive adsorption phenomena such as negative gas adsorption (NGA). NGA materials are bistable frameworks where the occurrence of a metastable overloaded state leads to pressure lification upon a sudden framework contraction. How can we control activation barriers and energetics via functionalization of the molecular building blocks that dictate the frameworks’ 30 mechanical response? In this work we tune the elastic and inelastic properties of building blocks at the 31 molecular level and analyze the mechanical response of the resulting frameworks. From a set of 11 frameworks, we demonstrate that widening of the backbone increases elasticity, while elongation of the building blocks results in a decrease in critical yield stress of buckling. We further functionalize the backbone by incorporation of sp3 hybridized carbon atoms to soften the molecular building blocks, or stiffen them with sp2 and sp carbons. Computational modeling shows how these modifications of the building blocks tune the 36 activation barriers within the energy landscape of the guest-free bistable frameworks. Only frameworks with free energy barriers in the range of 800 to 1100 kJ mol–1 37 per unit cell, and moderate yield stress of 0.6 to 38 1.2 nN for single ligand buckling, exhibit adsorption-induced contraction and negative gas adsorption. Advanced experimental in situ methodologies give detailed insights into the structural transitions and the adsorption behavior. The new framework DUT-160 shows the highest magnitude of NGA ever observed for nitrogen adsorption at 77 K. Our computational and experimental analysis of the energetics and mechanical response functions of porous frameworks is an important step towards tuning activation barriers in dynamic framework materials and provides critical design principles for molecular building blocks leading to pressure lifying materials
Publisher: Royal Society of Chemistry (RSC)
Date: 2021
DOI: 10.1039/D0FD00013B
Abstract: Adsorption-induced contraction and negative gas adsorption in the mesoporous metal–organic framework DUT-49 for different gases and temperatures.
Location: United Kingdom of Great Britain and Northern Ireland
No related grants have been discovered for Simon Krause.