Mobile Constituent-Boosted Dynamic Separation of C2H2/C2H4/CO2 Ternary Mixtures in Metal-Organic Frameworks.

The separation of acetylene (C2H2), ethylene (C2H4), and carbon dioxide (CO2) is critical in the chemical industry, driven by the increasing demand for high-purity C2H2 and C2H4. While metal-organic frameworks (MOFs) offer an energy-efficient approach for adsorptive gas separation, achieving sub-angstrom precision in pore size adjustment remains challenging. In this work, we leverage two synergistic mechanisms in a double-interpenetrated framework: (1) global structural flexibility, arising from dynamic displacement of subnetworks to tailor pore dimensions, and (2) local flexibility, enabled by counterion and ligand rotation, to modulate the aperture binding affinity for precise molecular discrimination. A series of isostructural MOFs, NUS-33-CF3SO3 and NUS-34-BF4, were designed to enable one-step purification of C2H4 and concurrent recovery of C2H2 from ternary gas mixtures. Within pores of optimal dimensions, the synergistic interplay between counterion-mediated host-guest interactions and local framework adaptability enables precise and simultaneous regulation of static and kinetic gas adsorption properties. Notably, NUS-34-BF4 achieves a dynamic C2H4 productivity of 2.62 mmol/g and a C2H2 uptake of 1.26 mmol/g. This study highlights the pivotal yet underexplored role of counterions as dynamic gatekeepers, offering a tunable strategy to engineer pore environments in flexible MOFs for advanced gas separations.