Aluminium isophthalate CAU-10-H is a promising stable adsorbent for application in heat-exchange processes.

The presented work aims at exploring the influence of the mobility of the sorbent framework on both the equilibrium and the kinetic properties of the sorbed phase by means of molecular dynamics computer experiments under isochoricÀisothermal and isobaricÀisothermal statistical ensembles for several host model options, combined by Widom averaging along the entire trajectory of the hostÀguest system toward rigorously obtained sorbate isotherms within a fully flexible lattice. The methodology is adapted to the study of the self-diffusivity and the collective (MaxwellÀStefan and transport) diffusivities of carbon dioxide (CO 2 ) and methane (CH 4 ) within the zeolite imidazolate framework-8 (ZIF-8). The simulation predictions are compared with measurements from pulsed-field gradient nuclear magnetic resonance (PFG NMR), as well as with recently conducted infrared microscopy (IRM) experiments elaborated on the basis of the current modeling in the flexible ZIF-8. The modeling results reveal a significant influence on sorbate transport exerted by the 2-methilimidazolate ligands surrounding the cage-to-cage entrances, whose apertures are commensurate with the guest molecular dimensions. Moreover, calculations of the singlet probability density distribution of the sorbate molecules at selected regions within the imidazolate framework provide a plausible explanation of the transport diffusivity as a function of sorbate occupancy, measured via IRM.

Self-diffusion measurements with methane and carbon dioxide adsorbed in the Zeolitic Imidazolate Framework-8 (ZIF-8) were performed by 1 H and 13 C pulsed field gradient nuclear magnetic resonance (PFG NMR). The experiments were conducted at 298 K and variable pressures of 7 to 15 bar in the gas phase above the ZIF-8 bed. Via known adsorption isotherms these pressures were converted to loadings of the adsorbed molecules. The self-diffusion coefficients of carbon dioxide measured by PFG NMR are found to be independent of loading. They are in good agreement with results from molecular dynamic (MD) simulations and resume the trend previously found by IR microscopy at lower loadings. Methane diffuses in ZIF-8 only slightly slower than carbon dioxide. Its experimentally obtained self-diffusion coefficients are about a factor of two smaller than the corresponding values determined by MD simulations using flexible frameworks.

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.