Topology-Directed Pore Space Compartmentalization and Densification in MOFs Enable Record Trace C3H6 Capture and C2H4 Purification

Abstract

Adsorptive separation of C3H6 from C2H4 is of great relevance yet highly challenging to the petrochemical industry, especially for trace C3H6 capture. Here, we constructed two metal–organic frameworks (MOFs), NKU-410 and NKU-411, through pillaring of the kgd- and hxl-topology supermolecular building layers (SBLs) comprised of a novel fluoride-bridging hexanuclear niccolite cluster. In terms of topological net merging and pillaring, a three-dimensional compartmentalization of pore space was implemented, reconstructing the less confined pore space in NKU-410 into a dense array of uniform strongly confined pore cavities in NKU-411. Leveraging the pore confinement effect, NKU-411 impressively attains an ultrahigh C3H6 uptake of 47.5 cm3 g–1 at 298 K and 0.01 bar, together with an appreciable C3H6/C2H4 (1/99, v/v) selectivity of 36.9, placing it among the benchmark MOFs for trace C3H6 capture from C2H4. Dynamic breakthrough experiments demonstrated that NKU-411 shows excellent C2H4 purification and C3H6 recovery performances at ambient conditions over a wide range of separation scenarios with varying feed concentrations and compositions, remarkably affording a record-breaking C2H4 (≥99.999% pure) productivity of 639.4 L kg–1 from C3H6/C2H4 (1/99, v/v) mixture. In-depth mechanistic studies disclosed that the well-tailored pore cavity in NKU-411 represents a “sweet spot” for C3H6 and the dense arrangement of such “sweet spot” maximally optimizes the pore space utilization, providing a new paradigm for boosting the ultralow-pressure gas adsorption capacity and selectivity for MOFs.