High-throughput gas separation by flexible metal–organic frameworks with fast gating and thermal management capabilities

Abstract

Establishing new energy-saving systems for gas separation using porous materials is indispensable for ensuring a sustainable future. Herein, we show that ELM-11 ([Cu(BF 4) 2 (4,4′bipyridine) 2 ] n), a member of flexible metal-organic frameworks (MOFs), exhibits rapid responsiveness to a gas feed and an 'intrinsic thermal management' capability originating from a structural deformation upon gas adsorption (gate-opening). These two characteristics are suitable for developing a pressure vacuum swing adsorption (PVSA) system with rapid operations. A combined experimental and theoretical study reveals that ELM-11 enables the high-throughput separation of CO 2 from a CO 2 /CH 4 gas mixture through adiabatic operations, which are extreme conditions in rapid pressure vacuum swing adsorption. We also propose an operational solution to the 'slipping-off' problem, which is that the flexible MOFs cannot adsorb target molecules when the partial pressure of the target gas decreases below the gate-opening pressure. Furthermore, the superiority of our proposed system over conventional systems is demonstrated.

Adsorption of Carbon Dioxide, Methane, and Nitrogen on Zn(dcpa) Metal-Organic Framework

“…Zn(dcpa) is an example of such materials. In these cases, an "osmotic subensemble" [15,[39][40][41][42] can be employed to describe the equilibrium between host structures when exposed to gaseous adsorbates. Alternatively, Ghysels et al [42] proposed another free energy model able to describe the thermodynamics of breathing phenomena in flexible materials.…”

Combining In Situ Techniques (XRD, IR, and 13C NMR) and Gas Adsorption Measurements Reveals CO2-Induced Structural Transitions and High CO2/CH4 Selectivity for a Flexible Metal–Organic Framework JUK-8

“… 18 − 24 Intrinsic flexibility improves selectivity, 25 − 27 considerably increases the working capacity, 28 , 29 enables self-accelerating CO sorption, 30 and influences gas separation. 31 However, examination of the transition mechanism caused by the external stimulus requires sophisticated in situ techniques, 32 e.g ., nuclear magnetic resonance (NMR), 33 powder X-ray diffraction (PXRD), 34 infrared spectroscopy 35 (IR), and others. 36 The obtained information serves as input for the understanding–tuning–developing cycle for adjusting the crucial features of the adsorbent for advanced applications.…”

Zr-MOFs for CF4/CH4, CH4/H2, and CH4/N2 separation: towards the goal of discovering stable and effective adsorbents

“…It is known that the flexibility of the structures can ease the diffusion of gas molecules into the pores and, in some cases, improve gas storage/separation performances of MOF adsorbents and membranes. [87][88][89] For instance, Witman et al's theoretical analysis 89 demonstrated that a judiciously designed flexible material can outperform the CH 4 delivery performance of rigid materials. Thus, ideally, MOFs should be modeled flexible.…”