Exploring the thermodynamic criteria for responsive adsorption processes

Evans, Jack D.; Krause, Simon; Kaskel, Stefan; Sweatman, Martin B.; Sarkisov, Lev

doi:10.1039/c9sc01299k

Cited by 43 publications

(51 citation statements)

References 39 publications

(47 reference statements)

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“…To qualitatively describe potential flexing modes in SPCs, a hinging model was used to determine flexible modes regardless of chemical composition . A toy model approach based on a slit pore was used to explore thermodynamic and kinetic aspects in responsive pores . The interplay between the adsorption properties of PCPs and SPCs with an elastic gas reservoir demonstrated the complex multistability of such a system that may be correlated to gas storage applications …”

Section: Synthesis Characterization and Prediction Of Spcs And Softmentioning

confidence: 99%

Chemistry of Soft Porous Crystals: Structural Dynamics and Gas Adsorption Properties

2020

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In this Minireview, we discuss the fundamental chemistry of soft porous crystals (SPCs) by characterizing their common structural features and the resulting structural softness and transitions. In particular, we focus on the recently emerging properties based on metastable transitions and those arising from local dynamics. By comparing the resulting adsorption properties to those of commonly applied rigid adsorbents, we highlight the potential of SPCs to revolutionize adsorption‐based technologies, considering our current understanding of the thermodynamic and kinetic aspects. We provide brief outlines for the experimental and computational characterization of such phenomena and offer an outlook toward next‐generation SPCs likely to be discovered in the next decade.

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Section: Synthesis Characterization and Prediction Of Spcs And Softmentioning

confidence: 99%

Chemistry of Soft Porous Crystals: Structural Dynamics and Gas Adsorption Properties

2020

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“…In the published literature, DUT-49 and DUT-50 are so far unique in their ability to sustain a guest-overloaded metastable state before they undergo adsorption-induced structural contraction leading to NGA and pressure amplification. According to previous experimental 36 and computational studies, 34 To test the porosity of the bulk materials and potential occurrence of adsorption-induced transitions, the desolvated MOF powders were analysed using nitrogen physisorption at 77 K. Grand Canonical Monte Carlo (GCMC) simulations for op and cp phase greatly facilitate the interpretation of the experimental adsorption isotherms (description of the simulation procedures and CIF files in ESI) (Figure 4). DUT-160 and DUT-161 stand out as highly porous materials with specific pore volumes up to 3.38 and 3.2 cm 3 g -1 and geometrically accessible surface areas of 5342 and 5229 m 2 g -1 , respectively determined by Zeo++ calculations 47 from the simulated crystal structures (Error!…”

Section: Analysis Of Adsorption Properties By Experiments and Simulationmentioning

confidence: 99%

“…Computational analysis showed that this behaviour can in principle be observed for other porous materials if their mechanical properties allow for bistability. 34 We subsequently investigated molecular changes to the DUT-49 structure in an effort to tune or change the inelastic mechanical response involved in this phenomenon. Motivated by the macroscopic understanding of columnar buckling, in recent studies we considered shortening 35 and elongation of the molecular struts.…”

Section: Introductionmentioning

confidence: 99%

Engineering Micromechanics of Soft Porous Crystals for Negative Gas Adsorption

Krause

Evans²,

Bon³

et al. 2020

Preprint

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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 amplification 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 amplifying materials<br>

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“…However, these molecular simulations in a complex pore system, such as DUT-49, are computationally very challenging. Instead, we recently demonstrated that thermodynamic and kinetic conditions for NGA can be modeled in a simple slit-pore toy model 15 .…”

Section: Adsorption Stress Model For Determination Of Low Temperaturementioning

confidence: 99%

“…The step-wise isotherms and switching of the solid is caused by highly inelastic transformations and an anharmonic potential energy function (Helmholtz Free Energy). 15 In recent years especially computational analysis has demonstrated that adsorption-induced structural transitions are a complex interplay between the structural flexibility of the MOF, as well as the solid-fluid and fluid-fluid interactions. [16][17][18] Beyond the nature of the solid and fluid, temperature effects were found to have a large impact on the presence of breathing in systems lie MIL-53 19,20 and ZIF-8 21 , however little experimental and computational work has been performed beyond these systems.…”

Section: Introductionmentioning

confidence: 99%

The Role of Temperature and Adsorbate on Negative Gas Adsorption in the Mesoporous Metal-Organic Framework DUT-49

Krause¹,

Evans²,

Bon³

et al. 2020

Preprint

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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.

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Exploring the thermodynamic criteria for responsive adsorption processes

Abstract: A general thermodynamic model to investigate responsive adsorption processes in flexible porous materials.

Cited by 43 publications

References 39 publications

Chemistry of Soft Porous Crystals: Structural Dynamics and Gas Adsorption Properties

Chemistry of Soft Porous Crystals: Structural Dynamics and Gas Adsorption Properties

Engineering Micromechanics of Soft Porous Crystals for Negative Gas Adsorption

The Role of Temperature and Adsorbate on Negative Gas Adsorption in the Mesoporous Metal-Organic Framework DUT-49

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