Pore Space Partition within a Metal-Organic Framework for Highly Efficient C2H2/CO2 Separation

Abstract

The pore space partition (PSP) approach has been employed to realize a novel porous MOF (FJU-90) with dual functionalities for the challenging C₂H₂/CO₂ separation under ambient conditions. By virtue of a triangular ligand (Tripp = 2,4,6-tris(4-pyridyl)pyridine), the cylindrical channels in the original FJU-88 have been partitioned into uniformly interconnected pore cavities, leading to the dramatically reduced pore apertures from 12.0 × 9.4 to 5.4 × 5.1 Ų. Narrowing down the pore sizes, the resulting activated FJU-90a takes up a very large amount of C₂H₂ (180 cm³ g^-1) but much less of CO₂ (103 cm³ g^-1) at 298 K and 1 bar, demonstrating it to be the best porous MOF material for this C₂H₂/CO₂ (50%:50%) separation in terms of the C₂H₂ gravimetric productivity. IAST calculations, molecular modeling studies, and simulated and experimental breakthrough experiments comprehensively demonstrate that the pore space partition strategy is a very powerful approach to constructing MOFs with dual functionality for challenging gas separation.

Figure 1.

Illustration of pore space partition (PSP) through symmetry- and size-matching-regulated ligand insertion. (a) Viewed along the crystallographic c axis of the cylindrical channel before and after partitioning. (b) Side view of the 1D cylindrical channel and trigonal bipyrimidal nanocages before and after partitioning. (c) Polyhedral drawing of the connected network in FJU-88 and FJU-90 before and after partitioning. Color code: Co, rose; O, red; N, light blue; C, gray or gold; Guest molecules and hydrogen atoms have been omitted for clarity.

Figure 2.

N₂ sorption isotherms (at 77 K) for FJU-88a and FJU-90a. (Inset) BET plots for FJU-90a.

Figure 3.

(a) C₂H₂ and CO₂ single-component adsorption isotherms of FJU-88a and FJU-90a at 298 K under 1 bar. (b) Comparison of the IAST calculations of the C₂H₂ uptake of FJU-90a versus those of previously reported best-performing materials for equimolar C₂H₂/CO₂ mixtures. (c) Transient breakthrough simulations for the separation of equimolar C₂H₂/CO₂ mixtures using FJU-90a at 298 K, with a partial pressure of 50 kPa for each. (d) The C₂H₂ gravimetrically captured productivity of FJU-90a in comparison to that of the best-performing MOF materials reported to date and the productivity values of these MOFs were calculated from the simulated column breakthrough curves.

Figure 4.

Experimental breakthrough curves for (a) an equimolar C₂H₂/CO₂ mixture and (b) a cycling test of the equimolar C₂H₂/CO₂ mixture in a packed column with FJU-90a at 298 K and 1 bar.