Molecular Dynamics Simulations of the “Breathing” Phase Transformation of MOF Nanocrystallites

Keupp, Julian; Schmid, Rochus

doi:10.26434/chemrxiv.8281082.v1

Cited by 13 publications

(15 citation statements)

References 6 publications

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“…In accordance, novel experimental investigations on flexible MOFs should consider crystal size and cycling effects and include these in experiments and discussion. In addition, we would like to motivate computational chemists to extend recent efforts [46] in developing strategies to analyze these phenomena in silico.…”

Section: Resultsmentioning

confidence: 99%

The impact of crystal size and temperature on the adsorption-induced flexibility of the Zr-based metal–organic framework DUT-98

Krause

Bon

et al. 2019

Beilstein J. Nanotechnol.

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In this contribution we analyze the influence of adsorption cycling, crystal size, and temperature on the switching behavior of the flexible Zr-based metal–organic framework DUT-98. We observe a shift in the gate-opening pressure upon cycling of adsorption experiments for micrometer-sized crystals and assign this to a fragmentation of the crystals. In a series of samples, the average crystal size of DUT-98 crystals was varied from 120 µm to 50 nm and the obtained solids were characterized by X-ray diffraction, infrared spectroscopy, as well as scanning and transmission electron microscopy. We analyzed the adsorption behavior by nitrogen and water adsorption at 77 K and 298 K, respectively, and show that adsorption-induced flexibility is only observed for micrometer-sized crystals. Nanometer-sized crystals were found to exhibit reversible type I adsorption behavior upon adsorption of nitrogen and exhibit a crystal-size-dependent steep water uptake of up to 20 mmol g−1 at 0.5 p/p 0 with potential for water harvesting and heat pump applications. We furthermore investigate the temperature-induced structural transition by in situ powder X-ray diffraction. At temperatures beyond 110 °C, the open-pore state of the nanometer-sized DUT-98 crystals is found to irreversibly transform to a closed-pore state. The connection of crystal fragmentation upon adsorption cycling and the crystal size dependence of the adsorption-induced flexibility is an important finding for evaluation of these materials in future adsorption-based applications. This work thus extends the limited amount of studies on crystal size effects in flexible MOFs and hopefully motivates further investigations in this field.

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Section: Resultsmentioning

confidence: 99%

The impact of crystal size and temperature on the adsorption-induced flexibility of the Zr-based metal–organic framework DUT-98

Krause

Bon

et al. 2019

Beilstein J. Nanotechnol.

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“…Apparently, this barrier enhancement for dynamics resulting in rigidification of dynamic frameworks upon downsizing is a more general phenomenon than initially expected 66,79,80,86,89,91,92 . However, a theoretical framework explaining the textural origin of this rigidification is at a very early stage 86,[93][94][95] . Hypotheses for these enhanced barriers in downsized dynamic frameworks encompass contributions from (1) interfacial energy (surface energy, matrix effects, surface deformation, reduced density of the adsorbed phase in vicinity of the surface) as well as (2) cooperative effects (ferroic coupling effects, defects, twin boundaries, grain boundaries, suppressed nucleation etc.).…”

Section: Current Understanding Of Dynamic Phenomena In Metalorganic Fmentioning

confidence: 99%

Four-dimensional metal-organic frameworks

et al. 2020

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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. P orous framework materials offer outstanding functionality due to their wide range of tuneable building blocks and ultrahigh porosity 1-5. The integration of functions, such as chemisorptive, redox, optically or catalytically active centers, encapsulated drugs, enzymes, nanoparticles, and more, has led to the discovery of metal-organic framework (MOF) applications in gas separation, CO 2 sequestration, gas storage, catalysis, optics, and sensing, and a roadmap for integration into electronic systems has even been proposed 6-12. The chemistry of three-dimensional (3D) porous framework materials, connecting nodes and linkers through a variety of chemical bonds is enormously rich 13,14. While decades ago, rationalization was aided by topology analysis and isoreticular expansion 15,16 , in the age of digitalization computer-aided design plays a crucial role in predicting millions of new 3D structures and their properties 17-19. The serendipitous discovery of an adsorption induced structural transformation in a network nowadays termed ELM-11 20 stimulated researchers and laid the foundations for exploring novel dynamic phenomena in porous frameworks. Like enzymes, structural changes are stimulated by guest molecules intruding into the porous frameworks leading to macroscopic volume changes of up to 200-300%. The adaptive change of pore size is a fascinating feature, but a selectivity comparable to that of enzymes has not been reached yet. Emerging applications of adaptive porous materials Porosity switching in the crystalline solid state represents a unique phenomenon observed only in a limited number of porous materials 21-25. This flexibility was predicted in 1998 for MOFs by Kitagawa and coworkers, and later termed "3 rd Generation MOFs" 25-27. These materials are characterized by dynamic features of the framework structure and are also named "soft porous crystals" (SPCs). We briefly account here a few remarkable applications of the dynamic frameworks reported today as the premise for our following perspective (Fig. 1). In gas storage applications, the pore closing upon desorption provides almost ideal deliverable capacity, a key advantage compared with rigid adsorbents 28. More importantly, for gas separations, the selective response of the porous host in adapting the pore shape to a reco...

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“…This method has been widely used in previous studies in investigating the mechanical instability and dynamic effects of SPCs. 13,16,18,42,[56][57][58][59][60][61] The theories and simulation details of the P −V EOS method are provided in the Supporting Information.…”

Section: Resultsmentioning

confidence: 99%

Abnormal Effect of Phase Transition on Thermal Transport in Soft Porous Crystals

Ying

Zhong²

2021

Preprint

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Soft porous crystals (SPCs) can undergo large-amplitude phase transitions under external stimulus such as mechanical pressure, gas adsorption, and temperature while retaining their structural integrity. During the gas adsorption process, the generated latent heat is needed to be effectively removed. Thus, understanding the effect of phase transition on the thermal transport in SPCs becomes extremely important for their applications in storage and separation applications. In this paper, taking isorecticular DUT series as an example, the evolution of the thermal transport in SPCs during the phase transition from the large pore (lp) phase to the narrow pore (np) phase is comprehensively investigated by molecular dynamics (MD) simulations together with the Green-Kubo method. After the phase transition, an abnormal thermal transport property is found in the np phase of DUT materials. We find that although the transformed np phase of DUT-48 has a density much larger than its parent phase, the thermal conductivity of its np phase is smaller than its lp phase. This result is in contrast to the previous finding that SPCs with larger density possess a larger thermal conductivity. However, as for other DUT crystals including DUT-47, DUT-49, DUT-50, and DUT-151, the np phase is found to have a higher thermal conductivity than their lp phase counterpart, which is in accordance with the previous finding. This complicated effect of phase transition on thermal transport in SPCs can be explained by the porosity-dominated competition mechanism between the increased volumetric heat capacity and the aggravated phonon scattering during the phase transition process. Overall, the finding extracted from the present study can greatly expand current knowledge about the thermal conductivity of metal-organic frameworks that is previously found to grow usually with increasing porosity.

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Molecular Dynamics Simulations of the “Breathing” Phase Transformation of MOF Nanocrystallites

Cited by 13 publications

References 6 publications

The impact of crystal size and temperature on the adsorption-induced flexibility of the Zr-based metal–organic framework DUT-98

The impact of crystal size and temperature on the adsorption-induced flexibility of the Zr-based metal–organic framework DUT-98

Four-dimensional metal-organic frameworks

Abnormal Effect of Phase Transition on Thermal Transport in Soft Porous Crystals

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