Microporous metal–organic framework with open Cu2+ functional sites and optimized pore size for C2H2 storage and CH4 purification

Spatially Confined π-Complexation within Pore-Space-Partitioned Metal-Organic Frameworks for Enhanced Light Hydrocarbon Separation and Purification

Ultramicroporous metal-organic frameworks (MOFs) are demonstrated to be advantageous for the separation and purification of light hydrocarbons such as C2H2, C2H4, and CH4. The introduction of transition metal sites with strong π-complexation affinity into MOFs is more effective than other adsorption sites for the selective adsorption of π-electron-rich unsaturated hydrocarbon gases from their mixtures. However, lower coordination numbers make it challenging to produce robust MOFs directly utilizing metal ions with π-coordination activity, such as Cu+, Ag+, and Pd2+. Herein, a series of novel π-complexing MOFs (SNNU-33s) with a pore size of 4.6 Å are precisely constructed by cleverly introducing symmetrically matched C3-type [Cu(pyz)3] (pyz = pyrazine) coordinated fragments into 1D hexagonal channels of MIL-88 prototype frameworks. Benifit from the spatial confinement combined with π-complex-active Cu+ of [Cu(pyz)3], pore-space-partitioned SNNU-33 MOFs all present excellent C2H2/CH4, C2H4/CH4, and CO2/CH4 separation ability. Notably, the optimized SNNU-33b adsorbent demonstrates top-level IAST selectivity values for C2H2/CH4 (597.4) and C2H4/CH4 (69.8), as well as excellent breakthrough performance. Theoretical calculations further reveal that such benchmark light hydrocarbon separation and purification ability is mainly ascribed to the extra-strong binding affinity between Cu+ and π-electron donor molecules via a spatially confined π-complexation process.

Construction of two novel non-penetrating Co-MOFs derived from designed 2,4,6-tri(2,4-dicarboxyphenyl) pyridine: synthesis, structure and gas adsorption properties

The strategy of extending ligands and reducing symmetry provide a facile access to obtain a wide variety of linkers for the construction of MOFs bearing diverse structures and intriguing properties....

Metal-Organic Frameworks (MOFs) as methane adsorbents: From storage to diluted coal mining streams concentration

Ventilation Air Methane emissions (VAM) from coal mines lead to environmental concern because their high global warming potential and the loss of methane resources. VAM upgrading requires pre-concentration processes dealing with high flow rates of very diluted streams (<1% methane). Therefore, methane separation and concentration is technically challenging and has important environmental and safety concerns. Among the alternatives, adsorption on Metal-Organic Frameworks (MOFs) could be an interesting option to methane selective separation, due to its tuneable character and outstanding physical properties. Most of the works devoted to the methane adsorption on MOFs deal with methane storage. Therefore, these works were reviewed to determine the properties governing methane-MOF interactions. In addition, the metallic ions and organic linkers roles have been identified. With these premises, decisive effects in the methane adsorption selectivity in nitrogen/methane lean mixtures have been discussed, since nitrogen is the most concentrated gas in the VAM stream, and it is very similar to methane molecule. In order to fulfill this overview, the effect of other aspects, such as the presence of polar compounds (moisture and carbon dioxide), was also considered. In addition, engineering considerations in the operation of fixed bed adsorption units and the main challenges associated to MOFs as adsorbents were also discussed.

Two zinc metal-organic framework isomers based on pyrazine tetracarboxylic acid and dipyridinylbenzene for adsorption and separation of CO2 and light hydrocarbons

Two highly porous metal-organic framework isomers Zn₂(TCPP)(DPB) (1 and 2, H₄TCPP = 2,3,5,6-tetrakis(4-carboxyphenyl)pyrazine and DPB = 1,4-di(pyridin-4-yl)benzene) were successfully synthesized using different solvents and acid species to adjust the topologies of these two MOFs. Both of them were constructed by paddlewheel Zn₂(COO)₄, TCPP^4-, and DPB ligands. In compound 1, the Zn₂(COO)₄ paddlewheel units were fitted together by the TCPP^4- ligands to form two-dimensional layers, which were further connected by DPB ligands as pillars to construct a two-fold catenated 3D framework. In compound 2, the cross-linkage of Zn₂(COO)₄ paddlewheel units and TCPP^4- ligands resulted in a three-dimensional framework of Zn-TCPP, in which DPB ligands coordinated to two axial vertical dinuclear Zn₂(COO)₄. Both activated MOFs exhibited permanent porosity with high BET areas (1324 m² g^-1 for 1 and 1247 m² g^-1 for 2) and possessed narrow pore size distributions (0.93 nm for 1 and 1.02 nm for 2). Moreover, the adsorption behaviors of the two activated MOFs for CO₂ and light hydrocarbons (C1, C2, and C3) at low pressure were evaluated and favorable selectivity was proven for C₃H₈/C₃H₆ over CH₄. These two MOF materials reported in this study for selective CO₂ and light hydrocarbon capture have immense potential applications for environmental protection.

Two copper-based MOFs constructed from a linear diisophthalate linker: supramolecular isomerism and gas adsorption properties

A pair of MOF supramolecular isomers was constructed from a linear diisophthalate ligand, and one of them displayed promising potential for C₂H₂/CH₄ and CO₂/CH₄ separations.

Incorporation of bifunctional aminopyridine into an NbO-type MOF for the markedly enhanced adsorption of CO2 and C2H2 over CH4

An NbO-type MOF based on an aminopyridine-heterobifunctionalized diisophthalate linker was synthesized, displaying markedly enhanced C₂H₂ and CO₂ adsorption over CH₄ compared to its parent compound.