Fast diffusion and High C2H2 Capture in a 2D MOF with Oxygen-riched Wide Channels for Efficient C2H2/CO2 Separation

Fast diffusion and High C2H2 Capture in a 2D MOF with Oxygen-riched Wide Channels for Efficient C2H2/CO2 Separation

The separation of C2H2/CO2 presents an arduous challenge due to their similar physicochemical properties. In this study, we propose SUM-1(Zr), a two-dimensional layered MOF that effectively captures C2H2 molecules by utilizing electronegative oxygen as hydrogen bond donors and separates C2H2/CO2 mixtures by competitive adsorption between C2H2 and CO2 molecules. The adsorption capacity of SUM-1(Zr) for C2H2 was measured to be 3.07 mmol g−1 at 298 K and 1 bar, with an IAST selectivity for C2H2/CO2 reaching 3.33. Kinetic studies demonstrated faster diffusion rates of C2H2 and CO2 molecules in hexagonal channels with larger pore sizes. The electronegative oxygen atoms and –NH molecules in SUM-1(Zr) create a favorable adsorption environment for the guest molecules, while the –NH moiety in SUM-1(Zr) is oriented towards the narrow triangular channels, and the wide hexagonal channels contains numerous electronegative oxygen atoms that act as hydrogen bond donors, selectively trapping C2H2 molecules. Theoretical calculations indicate that C2H2 prefers to adsorb near the oxygen atoms in the wide hexagonal channels, forming multiple hydrogen bonds with the oxygen atoms in the two adjacent parallel layers. It is worth noting that the binding energies of these two types of channels for C2H2 are significantly higher than those for CO2, resulting in competitive adsorption between C2H2 and CO2. This study highlights the potential of utilizing the unique pore surface environment and competitive adsorption among diverse gas molecules for efficient separation of gas mixtures in MOFs.

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