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

Pillar-layered metal–organic frameworks (PLMOFs) are promising gas adsorbents due to their high designability. In this work, high CO 2 storage capacity as well as controllable C 2 H 2 /CO 2 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, CO 2 and C 2 H 2 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 cm 3 g –1, respectively, which surpass the values of most MOF adsorbents. Dynamic breakthrough experiments further indicate that PLMOFs 1–3 have controllable C 2 H 2 /CO 2 separation performance, which can successfully overcome the C 2 H 2 /CO 2 separation challenge. Specially, PLMOFs 1–3 can remove trace CO 2 (3%) from the C 2 H 2 /CO 2 mixture and produce high-purity ethylene (99.9%) in one step with the C 2 H 2 productivities of 1.68, 2.45, and 3.30 mmol g –1, respectively. GCMC simulations indicate that the superior CO 2 adsorption and unique C 2 H 2 /CO 2 separation performance are mainly ascribed to different degrees of CO 2 agglomeration in the ultramicropores of these PLMOFs.