Selective adsorption of C2H2 and CO2 from CH4 in an isoreticular series of MOFs constructed from unsymmetrical diisophthalate linkers and the effect of alkoxy group functionalization on gas adsorption

Abstract

For acetylene production and natural gas purification, the development of porous materials exhibiting highly selective C₂H₂/CH₄ and CO₂/CH₄ separations is very important but remains a major challenge. In this work, we employed three unsymmetrical diisophthalate ligands to construct an isoreticular series of copper-based MOFs exhibiting highly selective adsorption of C₂H₂ and CO₂ from CH₄ under ambient conditions. The gravimetric uptake capacities at 298 K and 1 atm vary from 171.7 to 200.4 cm³ (STP) per g for C₂H₂, and from 104.1 to 115.6 cm³ (STP) per g for CO₂. The IAST adsorption selectivity is in the range of 27.6–34.5 for an equimolar C₂H₂/CH₄ mixture, and 5.73–7.14 for an equimolar CO₂/CH₄ mixture at 298 K and 1 atm. These values are among the highest reported for MOFs constructed from bent diisophthalate ligands under the same conditions. The effect of alkoxy group functionalization on gas adsorption was also explored, revealing that compared to the parent compound, the alkoxy group functionalized MOFs exhibit a reduced uptake capacity but an improved adsorption selectivity. This work demonstrates that the three MOFs are promising materials for C₂H₂/CH₄ and CO₂/CH₄ separations, and provides a fundamental understanding of alkoxy group functionalization on gas adsorption properties.