Unraveling the thermodynamic conditions for negative gas adsorption in soft porous crystals

Abstract

Soft porous crystals (SPCs) are widely known for their intriguing properties and various counterintuitive phenomena such as negative linear compression, negative thermal expansion and negative gas adsorption (NGA). An intriguing case is the adsorption of methane in DUT-49 for which experimentally a drop in the amount of adsorbed particles was observed under increasing vapor pressure. It is yet unknown which specific systems can exhibit NGA under which thermodynamic conditions. Herein, a semi-analytical thermodynamic model is applied to determine the conditions required for NGA, including their sensitivity towards various system-specific parameters, and investigate the correlation with pressure-induced breathing. As such, it is found that certain non-breathing materials may exhibit breathing with NGA under application of a fixed mechanical pressure. Such meticulous control of multiple triggers for NGA can open the way to new applications such as tunable gas detection and pressure amplification.

Ab Initio Derived Force Fields for Zeolitic Imidazolate Frameworks: MOF-FF for ZIFs

“…20 Recently Vanduyfhuys et al extended the Quick-FF methodology in a way that also periodic reference data can be treated. 37 In this study we improved the MOF-FF methodology in several aspects to be able to parameterize force fields in respect to periodic reference data. We demonstrate its capabilities by parameterizing force fields for ZIFs of varying topology and chemical composition (ZIF-8, ZIF-8(H), ZIF-8(Cl) and ZIF-8(Br)).…”

Thermodynamic Modeling of the Selective Adsorption of Carbon Dioxide over Methane in the Mechanically Constrained Breathing MIL‐53(Cr)

“…Finally, as was shown in previous work, the pore volume was represented by means of a simple piecewise linear function expressed in terms of the unit cell volume. [37] In the remainder of this work, phase diagrams, coadsorption isotherms were constructed and the selectivity of CO 2 over CH 4 as a function of the vapor gas pressures of each component as well as the mechanical pressure was computed. To this end, the osmotic potential, equilibrium unit cell volume ,and number of adsorbed methane and carbon dioxide molecules after performing the Legendre transform expressing equilibrium with given chemical potentials CO2 and CH4 and external pressue P ext were computed.…”

“…In a previous study, it has been evidenced that the additional application of a mechanical pressure can be used to induce NGA in SPCs that do not exhibit adsorption-induced breathing in the absence of mechanical pressure. [37] Moreover, increasing the mechanical pressure even further subsequently induces breathing with positive gas adsorption (PGA). In other words, in terms of an increasing applied mechanical pressure, these SPCs exhibit subsequent regions of no breathing, NGA and PGA.…”

“…Furthermore, the SPC type of the material was very recently linked with the adsorption-induced behavior to set up a thought experiment to explore the impact of an additional mechanical pressure on NGA. [37] Given their fascinating adsorption properties, these breathing materials are also promising candidates to serve as efficient hosts for the separation of gas mixtures. More specifically, the separation of carbon dioxide from a given mixture is an important issue in the context of carbon capture and storage, [25] which is highly relevant in the quest for the mitigation of climate change.…”

Ab initio derived force fields for Zeolitic Imidazolate Frameworks: MOF-FF for ZIFs

“…51 the Quick-FF methodology in a way that also periodic reference data can be treated. 52 In this study we improved the MOF-FF methodology in several aspects in order to be able to parameterize force fields for ZIFs of varying topology and chemical composition (ZIF-8, ZIF-8(H), ZIF-8(Cl) and ZIF-8(Br)). Whereas several ad hoc potentials for ZIF-8 exist, specific parameter sets for the halogenated systems are not available.…”