Atomistic Simulation Studies on the Dynamics and Thermodynamics of Nonpolar Molecules within the Zeolite Imidazolate Framework-8

Abstract

Statistical-mechanics-based simulation studies at the atomistic level of argon (Ar), methane (CH(4)), and hydrogen (H(2)) sorbed in the zeolite imidazolate framework-8 (ZIF-8) are reported. ZIF-8 is a product of a special kind of chemical process, recently termed as reticular synthesis, which has generated a class of materials of critical importance as molecular binders. In this work, we explore the mechanisms that govern the sorption thermodynamics and kinetics of nonpolar sorbates possessing different sizes and strength of interactions with the metal-organic framework to understand the outstanding properties of this novel class of sorbents, as revealed by experiments published elsewhere. For this purpose, we have developed an in-house modeling procedure involving calculations of sorption isotherms, partial internal energies, various probability density functions, and molecular dynamics for the simulation of the sorbed phase over a wide range of occupancies and temperatures within a digitally reconstructed unit cell of ZIF-8. The results showed that sorbates perceive a marked energetic inhomogeneity within the atomic framework of the metal-organic material under study, resulting in free energy barriers that give rise to inflections in the sorption isotherms and guide the dynamics of guest molecules.

Understanding the adsorption mechanism of noble gases Kr and Xe in CPO-27-Ni, CPO-27-Mg, and ZIF-8

“…For comparison, the maximal uptake of methane CD 4 molecules was found to be 3 CD 4 molecules per Zn atom. 58 Also the experimentally determined positions for both Kr and Xe atoms correlate well with theoretically simulated positions for Ar atoms, 59 and results of grand canonical Monte Carlo simulations. 12 The adsorption of noble gases by MOFs is based on the polarizability of both possible adsorption sites of the MOF and the adsorbed noble gases.…”

A review: methane capture by nanoporous carbon materials for automobiles

“…CH 4 storage can be stabilized and improved using the pore structure [42][43][44][45] and high specific surface area [46] of adsorbents.…”

Recent Advances in Molecular Dynamics Simulations of Gas Diffusion in Metal Organic Frameworks

“…This was attributed to the smaller pores of ZIFs and their structural characteristic that causes larger steric hindrance. Pantatosaki and coworkers computed H 2 self diffusion in ZIF-8 using both LJ and FH potentials at 77 and 300 K. (Pantatosaki et al, 2010) The diffusivity predictions showed that quantum mechanical description of H 2 at ambient temperatures is unimportant whereas MD simulations showed a marked difference between the values obtained from the classical and quantum mechanical description at 77 K. A recent MD study computed self diffusivities of H 2 , CO 2 , CH 4 and N 2 in ZIF-2, ZIF-4, ZIF-5, ZIF-8 and ZIF-9. (Battisti et al, 2011) Results showed that gases except H 2 do not diffuse appreciably in ZIF-5 at least within the time interval of the MD calculations which makes ZIF-5 promising in H 2 separations as a molecular sieve.…”