Asymmetric Pore Windows in Pillar-Layered Metal–Organic Framework Membranes for H₂/CO₂ Separation

In this study, a novel ultramicroporous pillar-layered Ni-LAP-NH 2 [Ni 2 ( l -asp) 2 (Pz-NH 2 )] ( l -asp = l -aspartic acid, Pz-NH 2 = aminopyrazine) membranes on porous α-Al 2 O 3 tubes with high performance and good thermal stability was first fabricated using isostructural Ni-LAP[Ni 2 ( l -asp) 2 (Pz)] (Pz = pyrazine) crystals as seeds. Utilizing the principle of reticular chemistry, here, we introduced the active amino side group into the Ni-LAP frameworks by replacing the pillar-layered ligand Pz with Pz -NH 2 while maintaining the original Ni-LAP small pore size, and the amino side group induced a “steric hindrance” effect and the physical adsorption affinity, which synergistically delayed CO 2 penetration. It was found that the preferential (111) orientation Ni-LAP-NH 2 membrane (Z10) exhibited a high H 2 /CO 2 separation performance with a separation factor of 41.7 and H 2 permeance of 9.08 × 10 –8 mol·m –2 ·s –1 ·Pa –1 under optimal conditions. These MOF materials demonstrated potential for industrial H 2 purification due to their tunable pore structure and remarkable stability. Moreover, this strategy offers an effective approach to tailoring pillar-layered MOF membranes with targeted molecular sieving ability.