Fundamental Understanding of Negative Gas Adsorption in Mesoporous Solids: Towards threshold sensitive mechanical actuators

• Applicant: Professor Dr. Stefan Kaskel
• Subject Area: Solid State and Surface Chemistry, Material Synthesis
• Term: from 2017 to 2021
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 391704421

• Final Report Year: 2022

Final Report Abstract

This project targeted a fundamental understanding of so called “negative gas adsorption” phenomena in mesoporous solids. Negative gas adsorption is a counterintuitive phenomenon in the field of porous materials, in particular flexible metal-organic frameworks. A bistable framework, which is more stable in the open pore form without guest, adsorbs a large amount of gas until a certain critical threshold pressure. At this pressure, p(NGA), the framework suddenly contracts and expels some of the molecules from its pores. In this project a key question was to understand which factors lead to a high or low amount of gas expelled for various gases and temperatures. The cooperation targeted a fundamental thermodynamic understanding through adsorption calorimetry and in situ methods based on porous model systems. A series of mesoporous frameworks, isostructural to DUT-49, was synthesized and characterized at TUD. Mechanical properties of the frameworks and in silico porosity calculations were conducted at ICGM. Calorimetric experiments, conducted at MADIREL revealed the energetics of the negative gas adsorption transitions. Finally, the pressure amplification experiments, conducted at TUD demonstrated the feasibility of DUT-49 and related frameworks for the pressure amplification applications. We achieved a fundamental understanding of mechanism, energetics, thermodynamics and micromechanics of NGA phenomena in DUT-49(Cu). The influence of metal, crystal size and defects was analyzed. A correlation between the micromechanical properties of the ligand molecule (stress/strain curves) and NGA properties of the respective MOFs was established. The impact of guest molecules and temperature on NGA shows a systematic relation of critical temperature (Tc) of the gas and the temperature at which the amount of expelled gas is at maximum. Important insights into the switching mechanism upon NGA were obtained from in situ NMR, in situ EPR and in situ UV-vis experiments. General thermodynamic criteria for NGA transitions as well as a complete thermodynamic landscape for DUT-49 were evaluated. Besides the fundamental interest of this breathing MOF, there are many possible technological applications including pneumatic devices, stimuli-responsive self-propelling systems or mechanical actuators responding selectively to changes in the environment, and capable of transforming a large amount of latent strain into pressure.

Publications

• Adsorption Contraction Mechanics: Understanding Breathing Energetics in Isoreticular Metal-Organic Frameworks, J. Phys. Chem. C 2018, 122, 19171-19179
  S. Krause, J. D. Evans, V. Bon, I. Senkovska, S. Ehrling, U. Stoeck, P. G. Yot, P. Iacomi, P. Llewellyn, G. Maurin, F.-X. Coudert and S. Kaskel
  
• The effect of crystallite size on pressure amplification in switchable porous solids, Nat. Commun. 2018, 9, 1573
  S. Krause, V. Bon, I. Senkovska, D. M. Toebbens, D. Wallacher, R. S. Pillai, G. Maurin and S. Kaskel
  
• High Pressure In Situ 129Xe NMR Spectroscopy: Insights into Switching Mechanisms of Flexible Metal-Organic Frameworks Isoreticular to DUT-49, Chem. Mater. 2019, 31, 16, 6193
  F. Kolbe, S. Krause, V. Bon, I. Senkovska, S. Kaskel, and E. Brunner
  
• Towards general network architecture design criteria for negative gas adsorption transitions in ultraporous frameworks, Nat. Commun. 2019, 10, 3632
  S. Krause, J. D. Evans, V. Bon, I. Senkovska, P. Iacomi, F. Kolbe, S. Ehrling, E. Troschke, J. Getzschmann, D. M. Toebbens, A. Franz, D. Wallacher, P. G. Yot, G. Maurin, E. Brunner, P. L. Llewellyn, F.-X. Coudert and S. Kaskel
  
• Engineering micromechanics of soft porous crystals for negative gas adsorption, Chem. Sci. 2020, 11, 9468
  S. Krause, J. D. Evans, V. Bon, I. Senkovska, S. Ehrling, P. Iacomi, D. M. Tobbens, D. Wallacher, M. S. Weiss, B. Zheng, P. G. Yot, G. Maurin, P. L. Llewellyn, F.-X. Coudert, S. Kaskel
  
• Low Temperature Calorimetry Coupled with Molecular Simulations for an In-Depth Characterization of the Guest-Dependent Compliant Behavior of MOFs, Chem. Mater. 2020, 32, 3489
  P. Iacomi, B. Zheng, S. Krause, S. Kaskel, G. Maurin, P. L. Llewellyn
  
• Tunable Flexibility and Porosity of the Metal–Organic Framework DUT-49 through Postsynthetic Metal Exchange, Chem. Mater. 2020, 32, 2, 889–896
  B. Garai, V. Bon, S. Krause, F. Schwotzer, M. Gerlach, I. Senkovska, S. Kaskel
  
• Integration of Fluorescent Functionality into Pressure-Amplifying Metal–Organic Frameworks, Chem. Mater. 2021, 33, 20, 7964– 7971
  F. Walenszus, J. D. Evans, V. Bon, F. Schwotzer, I. Senkovska, S. Kaskel
  
• Massive Pressure Amplification by Stimulated Contraction of Mesoporous Frameworks, Angew. Chem. Int. Ed. 2021, 60, 11735
  V. Bon, S. Krause, I. Senkovska, N. Grimm, D. Wallacher, D. M. Tobbens, S. Kaskel
  
• The role of temperature and adsorbate on negative gas adsorption in the mesoporous metalorganic framework DUT-49, Faraday Discuss. 2021, 225, 168-183
  S. Krause, J. Evans, V. Bon, I. Senkovska, F.-X. Coudert, D. Többens, D. Wallacher, N. Grimm, S. Kaskel