Abstract
AbstractAdsorption hysteresis is a phenomenon related to phase transitions that can impact applications such as gas storage and separations in porous materials. Computational approaches can greatly facilitate the understanding of phase transitions and phase equilibria in porous materials. In this work, adsorption isotherms for methane, ethane, propane, and n-hexane were calculated from atomistic grand canonical Monte Carlo (GCMC) simulations in a metal-organic framework having both micropores and mesopores to better understand hysteresis and phase equilibria between connected pores of different size and the external bulk fluid. At low temperatures, the calculated isotherms exhibit sharp steps accompanied by hysteresis. As a complementary simulation method, canonical (NVT) ensemble simulations with Widom test particle insertions are demonstrated to provide additional information about these systems. The NVT+Widom simulations provide the full van der Waals loop associated with the sharp steps and hysteresis, including the locations of the spinodal points and points within the metastable and unstable regions that are inaccessible to GCMC simulations. The simulations provide molecular-level insight into pore filling and equilibria between high- and low-density states within individual pores. The effect of framework flexibility on adsorption hysteresis is also investigated for methane in IRMOF-1.
Funder
U.S. Department of Energy
Publisher
Springer Science and Business Media LLC
Subject
Materials Chemistry,Biochemistry,Environmental Chemistry,General Chemistry
Reference72 articles.
1. van der Waals, J. The Equation of State for Gases and Liquids. Nobel Lectures, Physics 1901–1921.
2. Palmer, J. C., Poole, P. H., Sciortino, F. & Debenedetti, P. G. Advances in computational studies of the liquid–liquid transition in water and water-like models. Chem. Rev. 118, 9129–9151 (2018).
3. Orbey, H. & Sandler, S. Modeling Vapor-Liquid Equilibria Cubic Equations of State and Their Mixing Rules; Cambridge Series in Chemical Engineering; Cambridge University Press, 1998.
4. Ashraf, S. et al. Recent progress on water vapor adsorption equilibrium by metal-organic frameworks for heat transformation applications. Int. Commun. Heat Mass Transfer 124, 105242 (2021).
5. de Lange, M. F., Verouden, K. J. F. M., Vlugt, T. J. H., Gascon, J. & Kapteijn, F. Adsorption-driven heat pumps: the potential of metal–organic frameworks. Chem. Rev. 115, 12205–12250 (2015).