A calcium-based microporous metal-organic framework for efficient adsorption separation of light hydrocarbons

Ideal metal-organic frameworks (MOFs) are those have not only significant adsorption separation performances but also excellent vapor and/or thermal stability. In this work, a calcium-based metal-organic framework with high vapor-stability and thermostability, Ca(squarate), was prepared using readily available precursor (CaCO3) and squaric acid as starting materials by hydrothermal method. Characterization techniques including PXRD, TGA and BET surface area analysis reveal that this MOF remains stable no matter whether it was soaked in water or exposed to air for as long as 2 weeks. Moreover, the studied MOF material is capable of discriminating C-2 hydrocarbon molecules as it has an appropriate pore diameter around 3.4 angstrom. Excellent efficient separation for C2H2/C2H4 mixture (50:50, v/v) with an adsorption selectivity of 8.1 was realized at room temperature and ambient pressure, on the other hand, it also displayed a good separation performance for C2H4/C4H6 mixture (50:50, v/v) with an adsorption selectivity of 5.9. Furthermore, adsorption mechanism of C-2 hydrocarbons in this framework was investigated by the DFT-D calculation. The results revealed that this framework discriminated light hydrocarbons as a result of different interaction strength between hydrocarbons and framework that mainly arise from pi-pi interactions.