A generalized van der Waals model for light gas adsorption prediction in IRMOFs

By making reasonable simplifications to the structures of isoreticular metal-organic frameworks (IRMOFs) and defining important attractive regions of square-well potential, an adsorption model derived from the generalized van der Waals partition function is proposed to describe the isotherms of light gas adsorption in IRMOFs. The simplification of the structures is based on the geometries of the accessible surfaces and the dimensions of the frameworks, and the locations of the attractive regions are defined by examining the distribution of the adsorbate molecules. Grand Canonical Monte Carlo (GCMC) simulations using the simplified structures with square-well potentials and the complete atomic structures with Lennard-Jones and coulombic potentials are performed and compared to verify the reliability of the simplification. The adsorption model proposed in this work can predict adsorption isotherms of IRMOFs accurately by calculating the adsorbed amounts in different attractive regions of the simplified frameworks. It is also demonstrated that the model with the five parameters fitted to the adsorption isotherm at one temperature can accurately predict the isotherms at other temperatures.