Extra-High CO2 Adsorption and Controllable C2H2/CO2 Separation Regulated by the Interlayer Stacking in Pillar-Layered Metal–Organic Frameworks

Abstract

Pillar-layered metal–organic frameworks (PLMOFs) are promising gas adsorbents due to their high designability. In this work, high CO₂ storage capacity as well as controllable C₂H₂/CO₂ separation ability are acquired by rationally manipulating the interlayer stacking in pillar-layered MOF materials. The rational construction of pillar-layered MOFs started from the 2D Ni-BTC-pyridine layer, an isomorphic structure of pioneering MOF-1 reported in 1995. The replacement of terminal pyridine groups by bridging pyrazine linkers under optimized solvothermal conditions led to three 3D PLMOFs with different stacking types between adjacent Ni-BTC layers, named PLMOF 1 (ABAB stacking), PLMOF 2 (AABB stacking), and PLMOF 3 (AAAA stacking). Regulated by the layer arrangements, CO₂ and C₂H₂ adsorption capacities (273 K and 1 bar) of PLMOFs 1–3 vary from 173.0/153.3, 185.0/162.4, to 203.5/159.5 cm³ g^–1, respectively, which surpass the values of most MOF adsorbents. Dynamic breakthrough experiments further indicate that PLMOFs 1–3 have controllable C₂H₂/CO₂ separation performance, which can successfully overcome the C₂H₂/CO₂ separation challenge. Specially, PLMOFs 1–3 can remove trace CO₂ (3%) from the C₂H₂/CO₂ mixture and produce high-purity ethylene (99.9%) in one step with the C₂H₂ productivities of 1.68, 2.45, and 3.30 mmol g^–1, respectively. GCMC simulations indicate that the superior CO₂ adsorption and unique C₂H₂/CO₂ separation performance are mainly ascribed to different degrees of CO₂ agglomeration in the ultramicropores of these PLMOFs.