A Two-Dimensional Stacked Metal-Organic Framework for Ultra Highly-Efficient CO₂ Sieving

Carbon capture from flue gas and natural gas benefits to make the most of resource gases and alleviate global warming, though achieving ultra-high selectivities to sieve CO₂ from CH₄ and N₂ remains a challenge. To this end, MOFs with delicate size-exclusive pores and inherent functional groups may give birth to efficient CO₂ sieving sorbents, with intriguing CO₂ selectivities and capacities. Herein, we report a two-dimensional stacked indium-based MOF, i.e., In(aip)₂, with functional –NH₂ groups and channels around 3.57 Å to specifically trap CO₂, with a uptake over 1.27 mmol/g at 298 K and 101 kPa. Indeed, In(aip)₂ possesses amazingly-high IAST selectivities for CO₂/CH₄ (≈1808), and CO₂/N₂ (≈2635) at 298 K and 101 kPa, at least a magnitude superior to most of other MOF materials reported to date. The following static/dynamic sorption measurements corroborated the separation properties of this material, with purity gas (ca. 99 %) of CO₂ once released. In-depth theoretical calculations further demonstrated the host–guest interactions, as facilitated by hydrogen bonding, for CO₂ sieving. Our principle to design and identify MOF materials in this study proved an inspiring route to prepare highly-efficient CO₂ sieving sorbents.