Free Energy Landscapes and Metastability in Methane Adsorption within a Representative Metal-Organic Framework
Anthony Dorhauer1,2, Malgorzata Stankiewicz3,4, Bartosz Mazur4
1Deptartment of Physics & Astronomy, University of Missouri, Columbia, Missouri 65211, United States.
ACS Omega
|January 5, 2026
Summary
Metal-organic frameworks (MOFs) show complex methane adsorption behavior. Transition-Matrix Monte Carlo simulations reveal metastable states and cooperative rearrangements, clarifying adsorption thermodynamics in nanoporous materials.
Area of Science:
- Materials Science
- Chemical Physics
- Computational Chemistry
Background:
- Metal-organic frameworks (MOFs) offer tunable porosity and high surface area, making them promising for gas storage.
- Adsorption in MOFs exhibits complex behavior due to confinement effects, particularly for gases like methane (CH4).
Purpose of the Study:
- To investigate methane adsorption in an IRMOF-8 model under subcritical conditions.
- To elucidate the thermodynamic origins of metastability and hysteresis in confined adsorption using advanced simulation techniques.
Main Methods:
- Employed Grand Canonical Monte Carlo (GCMC) and Transition-Matrix Monte Carlo (TMMC) simulations.
- Utilized TMMC to directly compute the free-energy profile of methane uptake (Ω-(N)) in IRMOF-8.
- Analyzed cooperative rearrangements in the adsorbed methane phase.
Main Results:
- Observed sharp transitions in methane uptake (N) between low- and high-density states, indicating metastable configurations.
- TMMC simulations revealed stable and metastable adsorption states, explaining hysteresis seen in GCMC.
- Linked uptake transitions to cooperative structural rearrangements of confined methane driven by adsorbate interactions.
Conclusions:
- Provided the first quantitative TMMC mapping of methane adsorption free energy in IRMOF-8.
- Demonstrated that metastable states and cooperative rearrangements are key to understanding confined adsorption phenomena.
- Established a transferable framework for analyzing complex adsorption in nanoporous solids.
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