ORCID Profile
0000-0001-9521-2601
Current Organisations
Universitat Bern
,
University of Adelaide
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Theory and Design of Materials | Reaction Kinetics and Dynamics | Catalysis and Mechanisms of Reactions | Macromolecular and Materials Chemistry
Expanding Knowledge in the Chemical Sciences | Expanding Knowledge in the Physical Sciences |
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: Royal Society of Chemistry (RSC)
Date: 2021
DOI: 10.1039/D1DT01477C
Abstract: The alkyl decorated MOF Zn 2 (TM-bdc) 2 (dabco) shows good adsorption selectivity towards ethane over ethylene, which was revealed by breakthrough, coadsorption and high pressure adsorption.
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: American Chemical Society (ACS)
Date: 02-11-2020
Publisher: American Chemical Society (ACS)
Date: 04-2015
DOI: 10.1021/JP512944R
Publisher: American Chemical Society (ACS)
Date: 25-08-2017
Publisher: American Chemical Society (ACS)
Date: 09-05-2016
DOI: 10.1021/JACS.6B02781
Abstract: The recently reported process of chiral induction in a metal-organic framework (MOF) by nonchiral guest adsorption, demonstrated on the prototypical MOF-5, may revolutionize the production of MOFs for enantioselective separation and catalysis. Herein, we describe an investigation employing multiscale molecular simulation to discover the microscopic mechanism of chiral induction and investigate the stability of the resulting framework. Our results explain how the molecular size and chemical nature of N-methyl-2-pyrrolidone (NMP) give rise to the chiral transformation in MOF-5, whereas it cannot occur for other guest molecules, such as N,N-dimethylformamide (DMF). Moreover, we show that the guest-free CMOF-5 structure is energetically unstable, with either the achiral conventional structure or a closed pore structure preferred, demonstrating that chirality will not be retained upon activation of CMOF-5. While this limits the usability of chiral induction in MOFs, our study opens new avenues for the use of other guest molecules and provides microscopic insight into this unexpected outcome of guest-framework interactions in a soft porous crystal.
Publisher: American Chemical Society (ACS)
Date: 26-05-2021
DOI: 10.26434/CHEMRXIV.14291644
Abstract: Porosity and surface area analysis play a prominent role in modern materials science, where 123 their determination spans the fields of natural sciences, engineering, geology and medical 124 research. At the heart of this sits the Brunauer-Emmett-Teller (BET) theory,[1] which has been 125 a remarkably successful contribution to the field of materials science. The BET method was 126 developed in the 1930s and is now the most widely used metric for the estimation of surface 127 areas of porous materials.[2] Since the BET method was first developed, there has been an 128 explosion in the field of nanoporous materials with the discovery of synthetic zeolites,[3] 129 nanostructured silicas,[4–6] metal-organic frameworks (MOFs),[7] and others. Despite its 130 widespread use, the manual calculation of BET surface areas causes a significant spread in 131 reported areas, resulting in reproducibility problems in both academia and industry. To probe 132 this, we have brought together 60 labs with strong track records in the study of nanoporous 133 materials. We provided eighteen adsorption isotherms and asked these researchers to 134 calculate the corresponding BET areas, resulting in a wide range of values for each one. We 135 show here that the reproducibility of BET area determination from identical isotherms is a 136 largely ignored issue, raising critical concerns over the reliability of reported BET areas in 137 the literature. To solve this major issue, we have developed a new computational approach 138 to accurately and systematically determine the BET area of nanoporous materials. Our 139 software, called BET Surface Identification (BETSI), expands on the well-known Rouquerol 140 criteria and makes, for the first time, an unambiguous BET area assignment possible.
Publisher: Wiley
Date: 11-09-2023
Abstract: We report flexible [Pd(L)2]2+ complexes where there is self‐recognition, driven by π ‐ π interactions between electron‐rich aromatic arms and the cationic regions they are tethered to. This self‐recognition h ers the association of these molecules with aromatic molecular targets in solution. In one case, this complex can be reversibly converted to an ‘open’ [Pd2(L)2]4+ macrocycle through introduction of more metal ion. This is accomplished by the ligand having two bidentate binding sites: a 2‐pyridyl‐1,2,3‐triazole site, and a bis‐1,2,3‐triazole site. Due to favourable hydrogen bonding, the 2‐pyridyl‐1,2,3‐triazole units reliably coordinate in the [Pd(L)2]2+ complex to control speciation: a second equivalent of Pd(II) is required to enforce coordination to bis‐triazole sites and form the macrocycle. The macrocycle interacts with a molecular substrate with higher affinity. In this fashion we are able to use stoichiometry to reversibly switch between two different species and regulate guest binding.
Publisher: American Chemical Society (ACS)
Date: 04-09-2020
DOI: 10.26434/CHEMRXIV.12917933.V1
Abstract: The pillared layer framework DUT-8(Zn) (Zn 2 (2,6-ndc) 2 (dabco), 2,6-ndc = 2,6-naphthalenedicarboxylate, dabco = 1,4-diazabicyclo-[2.2.2]-octane, DUT = Dresden University of Technology) is a prototypical switchable MOF, showing characteristic adsorption and desorption induced open phase ( op ) to closed phase ( cp ) transformation associated with huge changes in cell volume. We demonstrate switchability strongly depends on a framework-specific critical particle size (d crit ). The solvent removal process (pore desolvation stress contracting the framework) significantly controls the cp / op ratio after desolvation and, subsequently, the adsorption induced switchability characteristics of the system. After desolvation, the dense cp phase of DUT-8(Zn) shows no adsorption-induced reopening and therefore is non-porous for N 2 at 77 K and CO 2 at 195 K. However, polar molecules with a higher adsorption enthalpy, such as the polar molecules such as chloromethane at 249 K and dichloromethane (DCM) at 298 K can reopen the macro-sized crystals upon adsorption. For macro-sized particles, the outer surface energy is negligible and only the type of metal (Zn, Co, Ni) controls the DCM-induced gate opening pressure. The framework stiffness increases from Zn to Ni as confirmed by DFT calculations, X-ray crystal structural analyses, and low frequency Raman spectroscopy. The partial disintegration of the Zn based node hinges produces an overall increased stabilization of cp vs. op phase shifts the critical particle size at which switchability starts to become suppressed to even lower values (d crit 200 nm) as compared to the Ni-based system ( d crit ≈ 500 nm). Hence, the three factors affecting switchability (energetics of the empty host, ( E op -E cp ) (I), particle size (II), and desolvation stress (III)) appear to be of the same order of magnitude and should be considered collectively, not in idually.
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: 20-07-2022
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: 21-06-2019
DOI: 10.26434/CHEMRXIV.8295878
Abstract: Most conventional materials display expansion upon heating, so there is considerable interest in identifying materials that display the opposite behavior, negative thermal expansion (NTE). In the current study, seven mesoporous metal-organic frameworks (MOFs) of varying topology and composition, which exhibit outstanding porosity, were investigated using molecular simulation for temperature-induced contraction. We find exceptional NTE for the most porous MOFs and a correlation between the coefficient of NTE and porosity. The large molecular subunits of the MOFs were further studied to find they intrinsically display NTE, corresponding to terahertz vibrational modes. As a result, NTE has a considerable effect on the mechanical properties of these MOFs and is an important consideration for understanding the mechanical stability of new extremely porous materials.
Publisher: Royal Society of Chemistry (RSC)
Date: 2014
DOI: 10.1039/C4CS00076E
Abstract: Post-synthetic metalation (PSMet) offers expansive scope for a targeted approach to tailoring the properties of MOFs.
Publisher: American Chemical Society (ACS)
Date: 27-05-2021
DOI: 10.26434/CHEMRXIV.14680335.V1
Abstract: The flexibility of soft porous crystals, i.e., their ability to respond to external stimuli with structural changes, is one of the most fascinating features of metal-organic frameworks. In addition to breathing and swelling phenomena of flexible MOFs, negative gas adsorption and pressure lification is one of the more recent discoveries in this field, initially observed in the cubic DUT-49 framework. In recent years the structural contraction was monitored by physisorption, X‑ray diffraction, NMR and EPR techniques, providing only limited information about the electronic structure of the ligand. In this work we designed a new ligand with a fluorescent core in the linker backbone and synthesized three new MOFs, isoreticular to DUT-49, denoted as DUT‑140(M) (M - Cu, Co, Zn) crystalizing in space group. DUT‑140(Cu) can be desolvated and is highly porous with an accessible apparent surface area of 4870 m2g-1 and a pore volume of 2.59 cm3g-1. Furthermore, it shows flexibility and NGA upon adsorption of subcritical gases. DUT-140(Zn), synthesized using post-synthetic metal exchange, could only be studied with guests in the pores. In addition to the investigation of the adsorption behavior of DUT-140(Cu) spectroscopic and computational methods were used to study the light absorption properties.
Publisher: Wiley
Date: 31-10-2023
Publisher: Royal Society of Chemistry (RSC)
Date: 2023
DOI: 10.1039/D3DT00085K
Abstract: The nature of metal in the isomorphous flexible DUT-8( M ) ([ M 2 (2,6-ndc) 2 (dabco)] n ) MOFs influences the flexibility, leading to the gate opening behaviour if M = Ni, Co, or Zn and to the breathing if M = Cu.
Publisher: Wiley
Date: 24-09-2018
Publisher: Springer Science and Business Media LLC
Date: 05-08-2021
Publisher: American Chemical Society (ACS)
Date: 11-02-2019
DOI: 10.26434/CHEMRXIV.7415249
Abstract: As the number of framework materials known and characterized in the literature grows, it becomes apparent that they can carry properties rarely encountered in more conventional, dense inorganic materials. Among these materials with unusual physical or chemical properties are the ubiquitous metal–organic frameworks, covalent organic frameworks, dense coordination polymers, and molecular frameworks. Many can respond to stimulation by displaying structural responses and changes in properties that range from counter-intuitive to thermodynamically forbidden. In that, they share large similarities with metamaterials, which are engineered to generate properties not found in “normal” materials. We review here the surprising behavior of these meta-MOFs and other framework materials that display properties “beyond” (μετά) the boundaries of common crystalline materials. br
Publisher: American Chemical Society (ACS)
Date: 25-07-2018
Publisher: Elsevier BV
Date: 06-2019
Publisher: Royal Society of Chemistry (RSC)
Date: 2016
DOI: 10.1039/C6CC04423A
Abstract: The synthesis and characterisation of two novel, endohedrally functionalised porous organic cages are presented.
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: 15-03-2021
DOI: 10.1021/JACS.1C00522
Publisher: Royal Society of Chemistry (RSC)
Date: 2013
DOI: 10.1039/C3DT00096F
Abstract: Dynamically porous metal-organic frameworks (MOFs) with a chiral quartz-based structure have been synthesized from the multidentate ligand 2,2'-dihydroxybiphenyl-4,4'-dicarboxylate (H2diol). Compounds [Ni(II)(H2diol)(S)2]·xS (where S = DMF or DEF) show marked changes in 77 K N2 uptake between partially desolvated [Ni(II)(H2diol)(S)2] (only the pore solvent is removed) and fully desolvated [Ni(II)(H2diol)] forms. Furthermore, [Ni(II)(H2diol)(DMF)2] displays additional solvent-dependent porosity through the rotation of DMF molecules attached to the axial coordination sites of the Ni(II) centre. A unique feature of the four coordinate Ni(II) centre in [Ni(II)(H2diol)] is the dynamic response to its chemical environment. Exposure of [Ni(II)(H2diol)] to H2O and MeOH vapour leads to coordination of both axial sites of the Ni centres and to the generation of a solvated framework, whereas exposure to EtOH, DMF, acetone, and MeCN does not lead to any change in metal coordination or structure metrics. MeOH vapour adsorption was able to be tracked by time-dependent magnetometry as the solvated and desolvated structures have different magnetic moments. Solvated and desolvated forms of the MOF show remarkable differences in their thermal expansivities [Ni(II)(H2diol)(DMF)2]·DMF displays marked positive thermal expansion (PTE) in the c-axis, yet near to zero thermal expansion, between 90 and 450 K, is observed for [Ni(II)(H2diol)]. These new MOF architectures demonstrate a dynamic structural and colourimetric response to selected adsorbates via a unique mechanism that involves a reversible change in the coordination environment of the metal centre. These coordination changes are mediated throughout the MOF by rotational mobility about the biaryl bond of the ligand.
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: American Chemical Society (ACS)
Date: 08-03-2018
DOI: 10.26434/CHEMRXIV.5962240
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: Proceedings of the National Academy of Sciences
Date: 12-01-2023
Abstract: Liquid methanol has the potential to be the hydrogen energy carrier and storage medium for the future green economy. However, there are still many challenges before zero-emission, affordable molecular H 2 can be extracted from methanol with high performance. Here, we present noble-metal-free Cu–WC/W plasmonic nanohybrids which exhibit unsurpassed solar H 2 extraction efficiency from pure methanol of 2,176.7 µmol g −1 h −1 at room temperature and normal pressure. Macro-to-micro experiments and simulations unveil that local reaction microenvironments are generated by the coperturbation of WC/W’s lattice strain and infrared-plasmonic electric field. It enables spontaneous but selective zero-emission reaction pathways. Such microenvironments are found to be highly cooperative with solar-broadband-plasmon-excited charge carriers flowing from Cu to WC surfaces for efficient stable CH 3 OH plasmonic reforming with C 3 -dominated liquid products and 100% selective gaseous H 2 . Such high efficiency, without any CO x emission, can be sustained for over a thousand-hour operation without obvious degradation.
Publisher: Royal Society of Chemistry (RSC)
Date: 2017
DOI: 10.1039/C7CS00084G
Abstract: Composed from discrete units, porous molecular materials (PMMs) possess properties not observed for conventional, extended solids. Molecular simulations provide crucial understanding for the design and characterisation of these unique materials.
Publisher: American Chemical Society (ACS)
Date: 18-01-2021
DOI: 10.26434/CHEMRXIV.13562798.V1
Abstract: New advanced adsorbents are a crucial driver for the development of energy and environmental applications. Tremendous potential is provided by machine learning and data mining techniques, as these approaches can identify the most appropriate adsorbent for a particular application. However, the current scientific reporting of adsorption isotherms in graphs and figures is not adequate to reproduce original experimentally measured data. This report proposes the specification of a new standard adsorption information file (AIF) inspired by the ubiquitous crystallographic information file (CIF) and based on the self-defining text archive and retrieval (STAR) procedure, also used to represent biological nuclear magnetic resonance experiments (NMR-STAR). The AIF is a flexible and easily extended free-format archive file that is readily human and machine readableand is simple to edit using a basic text editor or parse for database curation. This format represents the first steps toward an open adsorption data format as a basis for a decentralized adsorption data library. An open format facilitates the electronic transmission of adsorption data between laboratories, journals and larger databases, which is key in the effort to increase open science in the field of porous materials in the future.
Publisher: Royal Society of Chemistry (RSC)
Date: 2019
DOI: 10.1039/C9TA00825J
Abstract: The mechanism of water adsorption in the chemically and thermally stable DUT-67(Zr) framework was studied by neutron powder diffraction and optical calorimetry.
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: Royal Society of Chemistry (RSC)
Date: 2018
DOI: 10.1039/C8CE00337H
Abstract: Analysis of conformation polymorphism in cis -bis-triphenylphosphine complexes points to the importance of coordination numbers and homochirality of PPh 3 ligands.
Publisher: American Chemical Society (ACS)
Date: 23-05-2022
DOI: 10.26434/CHEMRXIV-2022-LS3RP
Abstract: Analysis of pore size distributions based on crystalline representations of metal-organic frameworks (MOFs) featuring hierarchical pore systems, DUT-32, DUT-75, UMCM-1 and NU-1000, is presented here and leveraged to understand gas adsorption in these unique pore structures. Statistical analysis was used to effectively partition the pore space into distinct regions labelled by the pore size. This pore description was used to discover how adsorbates are located, with respect to the different pores, during simulations of argon adsorption at 87K. To further examine adsorption behaviour, a method of clustering the pore environments to locate the centre of the pore was developed. These pore centres were employed to observe the distribution of gas within the pore, describing adsorbate positions during filling events from the unique perspective of the pore centre. The methods presented here provide unsurpassed information about pore structure and adsorption properties that cannot be obtained with currently available methods and are now ready to apply to new materials to uncover new adsorption processes.
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: American Chemical Society (ACS)
Date: 26-05-2021
DOI: 10.26434/CHEMRXIV.14291644.V2
Abstract: Porosity and surface area analysis play a prominent role in modern materials science, where 123 their determination spans the fields of natural sciences, engineering, geology and medical 124 research. At the heart of this sits the Brunauer-Emmett-Teller (BET) theory,[1] which has been 125 a remarkably successful contribution to the field of materials science. The BET method was 126 developed in the 1930s and is now the most widely used metric for the estimation of surface 127 areas of porous materials.[2] Since the BET method was first developed, there has been an 128 explosion in the field of nanoporous materials with the discovery of synthetic zeolites,[3] 129 nanostructured silicas,[4–6] metal-organic frameworks (MOFs),[7] and others. Despite its 130 widespread use, the manual calculation of BET surface areas causes a significant spread in 131 reported areas, resulting in reproducibility problems in both academia and industry. To probe 132 this, we have brought together 60 labs with strong track records in the study of nanoporous 133 materials. We provided eighteen adsorption isotherms and asked these researchers to 134 calculate the corresponding BET areas, resulting in a wide range of values for each one. We 135 show here that the reproducibility of BET area determination from identical isotherms is a 136 largely ignored issue, raising critical concerns over the reliability of reported BET areas in 137 the literature. To solve this major issue, we have developed a new computational approach 138 to accurately and systematically determine the BET area of nanoporous materials. Our 139 software, called BET Surface Identification (BETSI), expands on the well-known Rouquerol 140 criteria and makes, for the first time, an unambiguous BET area assignment possible.
Publisher: Wiley
Date: 11-08-2022
Abstract: DUT‐8(Ni) metal–organic framework (MOF) belongs to the family of flexible pillared layer materials. The desolvated framework can be obtained in the open pore form (op) or in the closed pore form (cp), depending on the crystal size regime. In the present work, we report on the behaviour of desolvated DUT‐8(Ni) at elevated temperatures. For both, op and cp variants, heating causes a structural transition, leading to a new, crystalline compound, containing two interpenetrated networks. The state of the framework before transition (op vs. cp) influences the transition temperature: the small particles of the op phase transform at significantly lower temperature in comparison to the macroparticles of the cp phase, transforming close to the decomposition temperature. The new compound, confined closed pore phase (ccp), was characterized by powder X‐ray diffraction and spectroscopic techniques, such as IR, EXAFS, and positron annihilation lifetime spectroscopy (PALS). Thermal effects of structural transitions were studied using differential scanning calorimetry (DSC), showing an overall exothermic effect of the process, involving bond breaking and reformation. Theoretical calculations reveal the energetics, driving the observed temperature induced phase transition.
Publisher: American Chemical Society (ACS)
Date: 31-03-2021
DOI: 10.26434/CHEMRXIV.14291644.V1
Abstract: Porosity and surface area analysis play a prominent role in modern materials science, where 123 their determination spans the fields of natural sciences, engineering, geology and medical 124 research. At the heart of this sits the Brunauer-Emmett-Teller (BET) theory,[1] which has been 125 a remarkably successful contribution to the field of materials science. The BET method was 126 developed in the 1930s and is now the most widely used metric for the estimation of surface 127 areas of porous materials.[2] Since the BET method was first developed, there has been an 128 explosion in the field of nanoporous materials with the discovery of synthetic zeolites,[3] 129 nanostructured silicas,[4–6] metal-organic frameworks (MOFs),[7] and others. Despite its 130 widespread use, the manual calculation of BET surface areas causes a significant spread in 131 reported areas, resulting in reproducibility problems in both academia and industry. To probe 132 this, we have brought together 60 labs with strong track records in the study of nanoporous 133 materials. We provided eighteen adsorption isotherms and asked these researchers to 134 calculate the corresponding BET areas, resulting in a wide range of values for each one. We 135 show here that the reproducibility of BET area determination from identical isotherms is a 136 largely ignored issue, raising critical concerns over the reliability of reported BET areas in 137 the literature. To solve this major issue, we have developed a new computational approach 138 to accurately and systematically determine the BET area of nanoporous materials. Our 139 software, called BET Surface Identification (BETSI), expands on the well-known Rouquerol 140 criteria and makes, for the first time, an unambiguous BET area assignment possible.
Publisher: Royal Society of Chemistry (RSC)
Date: 2022
DOI: 10.1039/D2CE00696K
Abstract: Analysis of metal–organic frameworks featuring hierarchical pore systems is presented and leveraged to understand adsorption in unique pore structures.
Publisher: Wiley
Date: 23-05-2022
Abstract: Porosity and surface area analysis play a prominent role in modern materials science. At the heart of this sits the Brunauer–Emmett–Teller (BET) theory, which has been a remarkably successful contribution to the field of materials science. The BET method was developed in the 1930s for open surfaces but is now the most widely used metric for the estimation of surface areas of micro‐ and mesoporous materials. Despite its widespread use, the calculation of BET surface areas causes a spread in reported areas, resulting in reproducibility problems in both academia and industry. To prove this, for this analysis, 18 already‐measured raw adsorption isotherms were provided to sixty‐one labs, who were asked to calculate the corresponding BET areas. This round‐robin exercise resulted in a wide range of values. Here, the reproducibility of BET area determination from identical isotherms is demonstrated to be a largely ignored issue, raising critical concerns over the reliability of reported BET areas. To solve this major issue, a new computational approach to accurately and systematically determine the BET area of nanoporous materials is developed. The software, called “BET surface identification” (BETSI), expands on the well‐known Rouquerol criteria and makes an unambiguous BET area assignment possible.
Publisher: Royal Society of Chemistry (RSC)
Date: 2019
DOI: 10.1039/C9TA06781G
Abstract: DUT-8(Co) shows a selective structural transition for CH 2 Cl 2 vs. CHCl 3 and CCl 4 at 298 K.
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: Royal Society of Chemistry (RSC)
Date: 2019
DOI: 10.1039/C9TA06644F
Abstract: Molecular simulations reveal that mesoporous metal–organic frameworks display large volumetric negative thermal expansion, which has a considerable effect on mechanical stability, outlining an alternative application for these ultra-porous materials.
Publisher: AIP Publishing
Date: 20-10-2023
DOI: 10.1063/5.0144827
Publisher: The Chemical Society of Japan
Date: 05-05-2015
DOI: 10.1246/CL.150021
Publisher: American Chemical Society (ACS)
Date: 07-01-2022
Publisher: American Chemical Society (ACS)
Date: 09-01-2014
DOI: 10.1021/JP4079184
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: 19-07-2012
DOI: 10.1021/JP301464S
Abstract: Coordination polymers and discrete metallo-supramolecular assemblies of hexaaryl[3]radialene compounds exhibit intriguing structures with short anion to π-centroid distances in the solid-state. Furthermore, these [3]radialene compounds display useful photophysical and electrochemical properties that make them ideal as potential platforms for anion receptors. In this study, hexafluoro[3]radialene was optimized to the MP2/aug-cc-pVTZ level of theory, and its complexes with halide anions were optimized to HF/6-31G++(d,p), MP2/6-31G++(d,p), M06-2X/6-31G++(d,p), and M06-2X/6-311G++(d,p) levels of theory. Hexafluoro[3]radialene was shown to have properties (large positive Qzz and areas of positive electrostatic surface potential) comparable to other compounds that show anion-π interactions. The interaction energies of complexes of hexafluoro[3]radialene with halide anions were calculated and found to be favorable and equivalent to those of fluorinated aromatic compounds. A series of synthetically accessible hexaaryl[3]radialenes were optimized to HF/6-31G++(d,p) theory and their complexes with halides optimized to the M06-2X/6-31G++(d,p) level of theory. The calculated properties of the electron-deficient hexaaryl[3]radialenes also show large positive Qzz quadrupole moments and two areas of positive potential at the [3]radialene core and the acidic aryl hydrogen atoms. The interaction energies of the complexes of hexaaryl[3]radialenes and halide anions were found to follow the trend F(-) > Cl(-) ≈ Br(-) and correlate with the electron-deficient nature of the [3]radialene. Close contacts were observed between the anion and the radialene core and the aryl hydrogen atoms, suggesting a combination of anion-π and hydrogen bonding is important. Mass spectrometry was used to experimentally observe the complexes of a number of hexaaryl[3]radialenes with F(-), Cl(-), and Br(-) predicted computationally. Anion-[3]radialene complexes were successfully detected, and the stability of the complexes in tandem MS/MS experiments was found to support the computational results.
Publisher: Wiley
Date: 24-09-2018
Abstract: A new mesoporous metal-organic framework (MOF DUT-60) was conceptually designed in silico using Zn
Publisher: Royal Society of Chemistry (RSC)
Date: 2016
DOI: 10.1039/C6CE00064A
Publisher: Royal Society of Chemistry (RSC)
Date: 2016
DOI: 10.1039/C5CC08336B
Abstract: Porous metal–organic polyhedra (MOPs), constructed from heterometallic Pd II –M II (M = Cu, Ni, Zn) paddlewheel nodes and 5- tert -butyl-1,3-benzenedicarboxylate organic links, were prepared in which the Pd II ions preferentially line the inner surface of the cage molecules.
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: 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.
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: Royal Society of Chemistry (RSC)
Date: 2021
DOI: 10.1039/D0CE01497D
Abstract: The main factors affecting switchability are identified for DUT-8(Zn): energetics of the host, particle size, and desolvation stress. They influence the flexible behaviour to the same order of magnitude and should be always considered collectively.
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: Wiley
Date: 23-08-2022
Abstract: Self‐assembly makes metallo‐interlocked architectures attractive targets, but being in equilibrium with smaller species means that they can suffer from dilution effects. We show that a junctioned system gives rise to a [Pd 4 (L) 2 ] 8+ trefoil entangled tetrahedron irrespective of concentration. Heating the s le reversibly shifts the equilibrium from the knot to an isomeric non‐interlocked dual metallo‐cycle, demonstrating that thermodynamic equilibria can still be exploited for switching even in the absence of concentration effects.
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: Elsevier BV
Date: 12-2016
Publisher: Springer Science and Business Media LLC
Date: 06-2020
DOI: 10.1038/S41467-020-16527-8
Abstract: Recognising timescale as an adjustable dimension in porous solids provides a new perspective to develop novel four-dimensional framework materials. The deliberate design of three-dimensional porous framework architectures is a developed field however, the understanding of dynamics in open frameworks leaves a number of key questions unanswered: What factors determine the spatiotemporal evolution of deformable networks? Can we deliberately engineer the response of dynamic materials along a time-axis? How can we engineer energy barriers for the selective recognition of molecules? Answering these questions will require significant methodological development to understand structural dynamics across a range of time and length scales.
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: American Chemical Society (ACS)
Date: 19-05-2020
Publisher: Royal Society of Chemistry (RSC)
Date: 2021
DOI: 10.1039/D0FD00012D
Abstract: Preordering of the linker site and utilising framework flexibility are critical to achieving high levels of metal loading during post-synthetic metalation.
Publisher: American Chemical Society (ACS)
Date: 23-03-2017
DOI: 10.1021/ACS.JPCLETT.7B00397
Abstract: Soft microporous materials exhibit properties, such as gated adsorption and breathing, which are highly desirable for many applications. These properties are largely studied for single crystals however, many potential applications expect to construct structured or composite systems, ex les of which include monoliths and mixed-matrix membranes. Herein, we use finite element methods to predict the macroscopic mechanical response of composite microporous materials. This implementation connects the microscopic treatment of crystalline structures to the response of a macroscopic s le. Our simulations reveal the bulk modulus of an embedded adsorbent within a composite is affected by the thickness and properties of the encapsulating layer. Subsequently, we employ this methodology to examine mixed-matrix membranes and materials of negative linear compressibility. This application of finite element methods allows for unprecedented insight into the mechanical properties of real-world systems and supports the development of composites containing mechanically anomalous porous materials.
Publisher: American Chemical Society (ACS)
Date: 2017
DOI: 10.26434/CHEMRXIV.5349151
Abstract: We show here that machine learning is a powerful new tool for predicting the elastic response of zeolites. We built our machine learning approach relying on geometric features only, which are related to local geometry, structure and porosity of a zeolite, to predict bulk and shear moduli of zeolites with an accuracy exceeding that of force field approaches. The development of this model has illustrated clear correlations between characteristic features of a zeolite and elastic moduli providing exceptional insight into the mechanics of zeolitic frameworks. Finally, we employ this methodology to predict the elastic response of 590 448 hypothetical zeolites, and the results of this massive database provide clear evidence to stability trends in porous materials.
Publisher: American Chemical Society (ACS)
Date: 11-09-2020
DOI: 10.26434/CHEMRXIV.12937820.V1
Abstract: In situ 1 H pulsed field gradient (PFG) NMR was used to investigate molecular diffusion of n-butane at 298 K during the negative gas adsorption (NGA) transition caused by contraction of the flexible metal-organic framework DUT-49(Cu). Supported by molecular dynamics simulations, it provided crucial insight to confined diffusion within a highly-flexible pore environment. The self-diffusion coefficients were derived from the experiment and compared with simulations, capturing the diffusion during n-butane adsorption and desorption. This complementary approach has yielded experimental characterization of molecular diffusion mechanisms during the unique process of NGA.
Publisher: American Chemical Society (ACS)
Date: 18-03-2019
DOI: 10.26434/CHEMRXIV.7527680
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: 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: 21-06-2019
DOI: 10.26434/CHEMRXIV.8295878.V1
Abstract: Most conventional materials display expansion upon heating, so there is considerable interest in identifying materials that display the opposite behavior, negative thermal expansion (NTE). In the current study, seven mesoporous metal-organic frameworks (MOFs) of varying topology and composition, which exhibit outstanding porosity, were investigated using molecular simulation for temperature-induced contraction. We find exceptional NTE for the most porous MOFs and a correlation between the coefficient of NTE and porosity. The large molecular subunits of the MOFs were further studied to find they intrinsically display NTE, corresponding to terahertz vibrational modes. As a result, NTE has a considerable effect on the mechanical properties of these MOFs and is an important consideration for understanding the mechanical stability of new extremely porous materials.
Publisher: American Chemical Society (ACS)
Date: 06-09-2016
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: 17-02-2021
DOI: 10.26434/CHEMRXIV.14036558
Abstract: A guest-induced flexibility in the framework DUT-13 was investigated in situ to analyze the breathing mechanism upon physisorption of nitrogen (77 K) and n-butane (273 K). The crystal structure of cp phase, solved from PXRD data using the computation-assisted semiempirical approach, shows two times smaller pore volume, compared to the op phase, which is consistent with the corresponding isotherms. The contraction mechanism is mainly based on the conformational isomerism of the benztb4- linker, which transforms from a staggered conformation in op phase to a more eclipsed in cp phase, leading to the contraction of the larger pore. A nearly complete op → cp → op transition was observed in the case of n-butane adsorption at 273 K, while in case of weakly interacting nitrogen molecules a portion of the s le remains in the op phase in the entire pressure range. Apparently, in case of DUT-13 the contraction is crystallite size-dependent, similarly as in a number of other switchable MOFs, which should be investigated more in detail in the future. Methane adsorption at varying temperatures showed a wide hysteresis at the temperatures between 111 K and 140 K. The hysteresis width decreases until it disappears completely at 170 K leading to a reversible isotherm, typical for rigid frameworks. The fact that breathing is observed in a broader temperature range in comparison to DUT‑49 demonstrates that thermodynamics and kinetics favour the DUT-13 contraction. Linker and hinges in DUT-13 are not stiff enough to support the metastable states required for NGA.
Publisher: American Chemical Society (ACS)
Date: 04-09-2020
DOI: 10.26434/CHEMRXIV.12917933
Abstract: The pillared layer framework DUT-8(Zn) (Zn sub /sub (2,6-ndc) sub /sub (dabco), 2,6-ndc = 2,6-naphthalenedicarboxylate, dabco = 1,4-diazabicyclo-[2.2.2]-octane, DUT = Dresden University of Technology) is a prototypical switchable MOF, showing characteristic adsorption and desorption induced open phase ( i op /i ) to closed phase ( i cp /i ) transformation associated with huge changes in cell volume. We demonstrate switchability strongly depends on a framework-specific critical particle size (d i sub crit /sub /i ). The solvent removal process (pore desolvation stress contracting the framework) significantly controls the i cp /i / i op /i ratio after desolvation and, subsequently, the adsorption induced switchability characteristics of the system. After desolvation, the dense i cp /i phase of DUT-8(Zn) shows no adsorption-induced reopening and therefore is non-porous for N sub /sub at 77 K and CO sub /sub at 195 K. However, polar molecules with a higher adsorption enthalpy, such as the polar molecules such as chloromethane at 249 K and dichloromethane (DCM) at 298 K can reopen the macro-sized crystals upon adsorption. For macro-sized particles, the outer surface energy is negligible and only the type of metal (Zn, Co, Ni) controls the DCM-induced gate opening pressure. The framework stiffness increases from Zn to Ni as confirmed by DFT calculations, X-ray crystal structural analyses, and low frequency Raman spectroscopy. The partial disintegration of the Zn based node hinges produces an overall increased stabilization of i cp /i vs. i op /i phase shifts the critical particle size at which switchability starts to become suppressed to even lower values (d i sub crit /sub /i 200 nm) as compared to the Ni-based system ( i d sub crit /sub /i ≈ 500 nm). Hence, the three factors affecting switchability (energetics of the empty host, ( i E sub op /sub -E sub cp /sub /i ) (I), particle size (II), and desolvation stress (III)) appear to be of the same order of magnitude and should be considered collectively, not in idually.
Publisher: Elsevier BV
Date: 2016
Publisher: Springer Science and Business Media LLC
Date: 27-05-2021
DOI: 10.1038/S41557-021-00684-4
Abstract: The ultrahigh porosity and varied functionalities of porous metal-organic frameworks make them excellent candidates for applications that range widely from gas storage and separation to catalysis and sensing. An interesting feature of some frameworks is the ability to open their pores to a specific guest, enabling highly selective separation. A prerequisite for this is bistability of the host structure, which enables the framework to breathe, that is, to switch between two stability minima in response to its environment. Here we describe a porous framework DUT-8(Ni)-which consists of nickel paddle wheel clusters and carboxylate linkers-that adopts a configurationally degenerate family of disordered states in the presence of specific guests. This disorder originates from the nonlinear linkers arranging the clusters in closed loops of different local symmetries that in turn propagate as complex tilings. Solvent exchange stimulates the formation of distinct disordered frameworks, as demonstrated by high-resolution transmission electron microscopy and diffraction techniques. Guest exchange was shown to stimulate repeatable switching transitions between distinct disorder states.
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: 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: Royal Society of Chemistry (RSC)
Date: 2023
DOI: 10.1039/D3CE00881A
Publisher: American Chemical Society (ACS)
Date: 02-04-2021
Publisher: American Chemical Society (ACS)
Date: 18-01-2021
DOI: 10.26434/CHEMRXIV.13562798
Abstract: New advanced adsorbents are a crucial driver for the development of energy and environmental applications. Tremendous potential is provided by machine learning and data mining techniques, as these approaches can identify the most appropriate adsorbent for a particular application. However, the current scientific reporting of adsorption isotherms in graphs and figures is not adequate to reproduce original experimentally measured data. / br / This report proposes the specification of a new standard adsorption information file (AIF) inspired by the ubiquitous crystallographic information file (CIF) and based on the self-defining text archive and retrieval (STAR) procedure, also used to represent biological nuclear magnetic resonance experiments (NMR-STAR). The AIF is a flexible and easily extended free-format archive file that is readily human and machine readable / and is simple to edit using a basic text editor or parse for database curation. This format represents the first steps toward an open adsorption data format as a basis for a decentralized adsorption data library. / br / An open format facilitates the electronic transmission of adsorption data between laboratories, journals and larger databases, which is key in the effort to increase open science in the field of porous materials in the future. /
Publisher: Wiley
Date: 31-10-2023
Publisher: Elsevier BV
Date: 02-2019
Publisher: American Chemical Society (ACS)
Date: 29-08-2017
DOI: 10.26434/CHEMRXIV.5349151.V1
Abstract: We show here that machine learning is a powerful new tool for predicting the elastic response of zeolites. We built our machine learning approach relying on geometric features only, which are related to local geometry, structure and porosity of a zeolite, to predict bulk and shear moduli of zeolites with an accuracy exceeding that of force field approaches. The development of this model has illustrated clear correlations between characteristic features of a zeolite and elastic moduli providing exceptional insight into the mechanics of zeolitic frameworks. Finally, we employ this methodology to predict the elastic response of 590 448 hypothetical zeolites, and the results of this massive database provide clear evidence to stability trends in porous materials.
Publisher: American Chemical Society (ACS)
Date: 17-02-2021
DOI: 10.26434/CHEMRXIV.14036558.V1
Abstract: A guest-induced flexibility in the framework DUT-13 was investigated in situ to analyze the breathing mechanism upon physisorption of nitrogen (77 K) and n-butane (273 K). The crystal structure of cp phase, solved from PXRD data using the computation-assisted semiempirical approach, shows two times smaller pore volume, compared to the op phase, which is consistent with the corresponding isotherms. The contraction mechanism is mainly based on the conformational isomerism of the benztb4- linker, which transforms from a staggered conformation in op phase to a more eclipsed in cp phase, leading to the contraction of the larger pore. A nearly complete op → cp → op transition was observed in the case of n-butane adsorption at 273 K, while in case of weakly interacting nitrogen molecules a portion of the s le remains in the op phase in the entire pressure range. Apparently, in case of DUT-13 the contraction is crystallite size-dependent, similarly as in a number of other switchable MOFs, which should be investigated more in detail in the future. Methane adsorption at varying temperatures showed a wide hysteresis at the temperatures between 111 K and 140 K. The hysteresis width decreases until it disappears completely at 170 K leading to a reversible isotherm, typical for rigid frameworks. The fact that breathing is observed in a broader temperature range in comparison to DUT‑49 demonstrates that thermodynamics and kinetics favour the DUT-13 contraction. Linker and hinges in DUT-13 are not stiff enough to support the metastable states required for NGA.
Publisher: Royal Society of Chemistry (RSC)
Date: 2021
DOI: 10.1039/D1QI00349F
Abstract: Rational selection of the delamination solvent enables efficient exfoliation of layered MOF, resulting in suspension of the nanosheets stable over days.
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: American Chemical Society (ACS)
Date: 06-10-2021
Publisher: Royal Society of Chemistry (RSC)
Date: 2021
DOI: 10.1039/D1SC04712D
Abstract: Stimuli-responsive metal–organic frameworks (MOFs) exhibit dynamic structural changes upon exposure to external stimuli. Here the coordination geometry of a post-synthetically added metal ion drastically changes the adsorption properties.
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: American Chemical Society (ACS)
Date: 05-12-2018
DOI: 10.26434/CHEMRXIV.7415249.V1
Abstract: As the number of framework materials known and characterized in the literature grows, it becomes apparent that they can carry properties rarely encountered in more conventional, dense inorganic materials. Among these materials with unusual physical or chemical properties are the ubiquitous metal–organic frameworks, covalent organic frameworks, dense coordination polymers, and molecular frameworks. Many can respond to stimulation by displaying structural responses and changes in properties that range from counter-intuitive to thermodynamically forbidden. In that, they share large similarities with metamaterials, which are engineered to generate properties not found in “normal” materials. We review here the surprising behavior of these meta-MOFs, that display properties “beyond” (μετά) the boundaries of common crystalline materials.
Publisher: American Chemical Society (ACS)
Date: 11-02-2019
DOI: 10.26434/CHEMRXIV.7415249.V2
Abstract: As the number of framework materials known and characterized in the literature grows, it becomes apparent that they can carry properties rarely encountered in more conventional, dense inorganic materials. Among these materials with unusual physical or chemical properties are the ubiquitous metal–organic frameworks, covalent organic frameworks, dense coordination polymers, and molecular frameworks. Many can respond to stimulation by displaying structural responses and changes in properties that range from counter-intuitive to thermodynamically forbidden. In that, they share large similarities with metamaterials, which are engineered to generate properties not found in “normal” materials. We review here the surprising behavior of these meta-MOFs and other framework materials that display properties “beyond” (μετά) the boundaries of common crystalline materials.
Publisher: American Chemical Society (ACS)
Date: 27-05-2021
DOI: 10.26434/CHEMRXIV.14680335
Abstract: The flexibility of soft porous crystals, i.e., their ability to respond to external stimuli with structural changes, is one of the most fascinating features of metal-organic frameworks. In addition to breathing and swelling phenomena of flexible MOFs, negative gas adsorption and pressure lification is one of the more recent discoveries in this field, initially observed in the cubic DUT-49 framework. In recent years the structural contraction was monitored by physisorption, X‑ray diffraction, NMR and EPR techniques, providing only limited information about the electronic structure of the ligand. In this work we designed a new ligand with a fluorescent core in the linker backbone and synthesized three new MOFs, isoreticular to DUT-49, denoted as DUT‑140(M) (M - Cu, Co, Zn) crystalizing in space group. DUT‑140(Cu) can be desolvated and is highly porous with an accessible apparent surface area of 4870 m2g-1 and a pore volume of 2.59 cm3g-1. Furthermore, it shows flexibility and NGA upon adsorption of subcritical gases. DUT-140(Zn), synthesized using post-synthetic metal exchange, could only be studied with guests in the pores. In addition to the investigation of the adsorption behavior of DUT-140(Cu) spectroscopic and computational methods were used to study the light absorption properties.
Publisher: American Chemical Society (ACS)
Date: 11-09-2020
DOI: 10.26434/CHEMRXIV.12937820
Abstract: In situ sup /sup H pulsed field gradient (PFG) NMR was used to investigate molecular diffusion of n-butane at 298 K during the negative gas adsorption (NGA) transition caused by contraction of the flexible metal-organic framework DUT-49(Cu). Supported by molecular dynamics simulations, it provided crucial insight to confined diffusion within a highly-flexible pore environment. The self-diffusion coefficients were derived from the experiment and compared with simulations, capturing the diffusion during n-butane adsorption and desorption. This complementary approach has yielded experimental characterization of molecular diffusion mechanisms during the unique process of NGA. br
Publisher: American Association for the Advancement of Science (AAAS)
Date: 15-04-2022
Abstract: Flexible metal-organic frameworks that show reversible guest-induced phase transitions between closed and open pore phases have enormous potential for highly selective, energy-efficient gas separations. Here, we present the gate-opening process of DUT-8(Ni) that selectively responds to D 2 , whereas no response is observed for H 2 and HD. In situ neutron diffraction directly reveals this pressure-dependent phase transition. Low-temperature thermal desorption spectroscopy measurements indicate an outstanding D 2 -over-H 2 selectivity of 11.6 at 23.3 K, with high D 2 uptake. First-principles calculations coupled with statistical thermodynamics predict the isotope-selective gate opening, rationalized by pronounced nuclear quantum effects. Simulations suggest DUT-8(Ni) to remain closed in the presence of HT, while it also opens for DT and T 2 , demonstrating gate opening as a highly effective approach for isotopolog separation.
Publisher: Wiley
Date: 21-05-2021
Abstract: The switching mechanism of the flexible framework Zn 4 O(benztb) 1.5 (benztb= N , N , N’ , N’ ‐benzidine tetrabenzoate), also known as DUT‐13, was studied by advanced powder X‐ray diffraction (PXRD) and gas physisorption techniques. In situ synchrotron PXRD experiments upon physisorption of nitrogen (77 K) and n ‐butane (273 K) shed light on the hitherto unnoticed guest‐induced breathing in the MOF. The mechanism of contraction is based on the conformationally labile benztb ligand and accompanied by a reduction in specific pore volume from 2.03 cm 3 g −1 in the open‐pore phase to 0.91 cm 3 g −1 in the contracted‐pore phase. The high temperature limit for adsorption‐induced contraction of 170 K, determined by systematic temperature variation of methane adsorption isotherms, indicates that the DUT‐13 framework is softer than other mesoporous MOFs like DUT‐49 and does not support the formation of overloaded metastable states required for negative gas‐adsorption transitions.
Publisher: Wiley
Date: 20-02-2013
Publisher: American Chemical Society (ACS)
Date: 10-07-2020
DOI: 10.1021/JACS.0C05286
Publisher: Royal Society of Chemistry (RSC)
Date: 2023
DOI: 10.1039/D3TA04707E
Publisher: Wiley
Date: 02-05-2023
Abstract: Micropatterning crystalline materials with oriented pores is necessary for the fabrication of devices with anisotropic properties. Crystalline and porous metal–organic frameworks (MOFs) are ideal materials as their chemical and structural mutability enables precise tuning of functional properties for applications ranging from microelectronics to photonics. Herein, a patternable oriented MOF film is designed: by using a photomask under X‐ray exposure, the MOF film decomposes in the irradiated areas, remaining intact in the unexposed regions. The MOF film acts simultaneously as a resist and as functional porous material. While the heteroepitaxial growth from aligned Cu(OH) 2 nanobelts is used to deposit oriented MOF films, the sensitivity to radiation is achieved by integrating a brominated dicarboxylate ligand (Br 2 BDC) into a copper‐based MOF Cu 2 L 2 DABCO (DABCO = 1,4‐diazabicyclo[2.2.2]octane L = BDC/Br 2 BDC). The lithographed s les act as diffraction gratings upon irradiation with a laser, thus confirming the quality of the extended MOF micropattern. Furthermore, the oriented MOF patterns are functionalized with fluorescent dyes. As a result, by rotating the polarization angle of the laser excitation, the alignment of the dye in the MOF is demonstrated. By controlling the functional response to light, this MOF patterning protocol can be used for the microfabrication of optical components for photonic devices.
Publisher: Wiley
Date: 07-05-2021
Abstract: The rate of charging of supercapacitors depends on how quickly ions can reach and accommodate the surface of electrodes. Diffusivity, a parameter reflecting the speed of ions’ migration, is believed to be crucial in designing supercapacitor electrodes. Herein, this belief is questioned, shedding light on a puzzling and potentially critical feature of ionic dynamics denoted as confinement‐induced ion–solvent separation. This effect can lead to a strong slowdown of the ion mobility inside hierarchical pore networks. Explanations for when such an effect occurs and how it can be circumvented are provided. Furthermore, this microscopic picture of diffusion seen by NMR is bridged with the macroscopic charging behavior of supercapacitors investigated by impedance spectroscopy. Quantifying the average residence time of ions within carbon particles shows that the nanopore environment may not be the rate‐limiting factor for the overall ion mobility and thus performance of a cell—as commonly expected. Combining direct diffusion studies performed with neat and solvated ionic liquids and those on organic electrolytes, the so far lacking criteria for the rational selection of electrolyte–carbon systems is developed and recommendations for the preparation of transport‐optimized materials for supercapacitors to minimize ionic diffusion limitations are given.
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
Start Date: 12-2022
End Date: 12-2025
Amount: $411,000.00
Funder: Australian Research Council
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