This work performs a systematic computational study toward a molecular understanding of the separation characteristics of metal-organic frameworks (MOFs), for which the purification of synthetic gas by two representative MOFs, MOF-5 and Cu-BTC, is adopted as an example. The simulations show that both geometry and pore size affect largely the separation efficiency, complex selectivity behaviors with different steps can occur in MOFs, and the electrostatic interactions that exist can enhance greatly the separation efficiency of gas mixtures composed of components with different chemistries. Furthermore, the macroscopic separation behaviors of the MOF materials are elucidated at a molecular level to give insight into the underlying mechanisms. The findings as well as the molecular-level elucidations provide useful microscopic information toward a complete understanding of the separation characteristics of MOFs that may lead to general design strategies for synthesizing new MOFs with tailored properties, as well as guiding their practical applications.

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The ligand functionalization effect on the CO(2)/CH(4) separation performance of the MOF type UiO-66(Zr) was explored computationally. The -SO(3)H and -CO(2)H functionalized forms show the highest selectivity, good working capacity and medium ranged CO(2) adsorption enthalpy that make these materials very promising for physisorption-based processes.

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In addition to its high thermal stability, repetitive hydration/dehydration tests have revealed that the porous zirconium terephthalate UiO-66 switches reversibly between its dehydroxylated and hydroxylated versions. The structure of its dehydroxylated form has thus been elucidated by coupling molecular simulations and X-ray powder diffraction data. Infrared measurements have shown that relatively weak acid sites are available while microcalorimetry combined with Monte Carlo simulations emphasize moderate interactions between the UiO-66 surface and a wide range of guest molecules including CH(4), CO, and CO(2). These properties, in conjunction with its significant adsorption capacity, make UiO-66 of interest for its further evaluation for CO(2) recovery in industrial applications. This global approach suggests a strategy for the evaluation of metal-organic frameworks for gas-based applications.

In this work a systematic computational study was performed to investigate the effects of organic linker, pore size and topology, and the electrostatic fields on the adsorption and diffusion behaviors of CO 2 in nine typical metal-organic frameworks (MOFs), showing that the high CO 2 storage capacity achieved in MOFs is a complex interplay of these structural properties. Under practical application conditions, MOFs show higher CO 2 storage capacity than both zeolites and carbon materials, and the suitable pore size is between 1.0 and 2.0 nm. For MOFs with pore size located in the above range, the larger the accessible surface area and free volume, the higher the CO 2 storage capacity can be achieved in practical applications. In addition, this work shows that the self-diffusivity of CO 2 in the MOFs is comparative in magnitude with that of zeolites.

Metal-organic frameworks (MOFs) have recently emerged as a new type of nanoporous materials with tailorable structures and functions. Usually, MOFs have uniform pores smaller than 2 nm in size, limiting their practical applications in some cases. Although a few approaches have been adopted to prepare MOFs with larger pores, it is still challenging to synthesize hierarchical-pore MOFs (H-MOFs) with high structural controllability and good stability. Here we demonstrate a facile and versatile method, an in situ self-assembly template strategy for fabricating stable H-MOFs, in which multi-scale soluble and/or acid-sensitive metal-organic assembly (MOA) fragments form during the reactions between metal ions and organic ligands (to construct MOFs), and act as removable dynamic chemical templates. This general strategy was successfully used to prepare various H-MOFs that show rich porous properties and potential applications, such as in large molecule adsorption. Notably, the mesopore sizes of the H-MOFs can be tuned by varying the amount of templates.