A two dimensional microporous metal-organic framework for selective gas separation

Exploration of porous metal-organic frameworks for gas separation and purification

As a new generation of porous materials, metal-organic frameworks (MOFs, also known as porous coordination polymers) have shown great promise for gas separation and purification because of their unique pore structures and surfaces for their differential recognition of small gas molecules. In this review article, we summarize our ongoing research endeavors to explore and discover microporous MOFs for gas separation and purification. We have developed several approaches to systematically tune the pores and to immobilize functional sites, including (1) the primitive cubic net of interpenetrated microporous MOFs from the self-assembly of the paddle-wheel clusters,M 2 ( C O 2 ) 4 ( M = C u 2 + , Z u 2 + … ) ), with two types of organic dicarboxylic acid and pillar bidentate linkers; (2) microporous mixed-metal-organic frameworks (M0 MOFs) through the metallo-ligands, and (3) microporous MOFs with dual functionalities. Such efforts have enabled us to make some breakthroughs on microporous MOFs for gas separation and purification, as demonstrated in the gas chromatographic separation of hexane isomers, kinetic D2/H2 separation, acetylene/ethylene separation, carbon dioxide capture, C2H2/CO2 and C3H4/C3H6 separation. Our group is one of the first groups who have envisioned the practical promise of microporous MOFs for the industrial gas separation and examined their separation capacities and efficiency using the fixed-bed adsorption and/or breakthrough experiments. Some of the very important and representative examples of these microporous MOFs for diverse gas separation and purification are highlighted in this review.

Effect of chemical structure of S-nitrosothiols on nitric oxide release mediated by the copper sites of a metal organic framework based environment

The effect of chemical structure of different biologically compatible S-nitrosothiols on the solvation environment at catalytic copper sites in a metal organic framework (MOF) suspended in a solution of ethanol is probed using computational methods. The use of a copper based MOF as a storage vehicle and catalyst (copper sites of the MOF) in the controlled and sustained release of chemically stored nitric oxide (NO) from S-nitrosocysteine has been shown to occur both experimentally and computationally [J. Am. Chem. Soc., 2012, 134, 3330-3333; Phys. Chem. Chem. Phys., 2015, 17, 23403]. Previous studies on a copper based MOF, namely HKUST-1, concluded that modifications in the R-group of s-nitrosothiols and/or organic linkers of MOFs led to a method capable of modulating NO release. In order to test the hypothesis that larger R-groups slow down NO release, four different RSNOs (R = cysteine, N-acetylcysteine, N-acetyl-d,l-penicillamine or glutathione) of varying size were investigated, which in turn required the use of a larger copper based MOF. Due to its desirable copper centers and more extensive framework, MOF-143, an analog of HKUST-1 was chosen to further explore both the effect of different RSNOs as well as MOF environments on NO release. Condensed phase classical molecular dynamics simulations are utilized to study the effect of the complex MOF environment as well as the chemical structure and size of the RSNO on the species on the catalytic reaction. The results indicate that in addition to the size of the RSNO species and the organic linkers within the MOF, the reaction rates can be modulated by the molecular structure of the RSNO and furthermore combining different RSNO species can also be used to tune the rate of NO release.

Ab initio molecular dynamics determination of competitive O₂ vs. N₂ adsorption at open metal sites of M₂(dobdc)

The separation of oxygen from nitrogen using metal-organic frameworks (MOFs) is of great interest for potential pressure-swing adsorption processes for the generation of purified O2 on industrial scales. This study uses ab initio molecular dynamics (AIMD) simulations to examine for the first time the pure-gas and competitive gas adsorption of O2 and N2 in the M2(dobdc) (M = Cr, Mn, Fe) MOF series with coordinatively unsaturated metal centers. Effects of metal, temperature, and gas composition are explored. This unique application of AIMD allows us to study in detail the adsorption/desorption processes and to visualize the process of multiple guests competitively binding to coordinatively unsaturated metal sites of a MOF.