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

In this study, a novel ultramicroporous pillar-layered Ni-LAP-NH₂ [Ni₂(l-asp)₂(Pz-NH₂)] (l-asp = l-aspartic acid, Pz-NH₂ = aminopyrazine) membranes on porous α-Al₂O₃ tubes with high performance and good thermal stability was first fabricated using isostructural Ni-LAP[Ni₂(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 -NH₂ 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 CO₂ penetration. It was found that the preferential (111) orientation Ni-LAP-NH₂ membrane (Z10) exhibited a high H₂/CO₂ separation performance with a separation factor of 41.7 and H₂ permeance of 9.08 × 10^-8 mol·m^-2·s^-1·Pa^-1 under optimal conditions. These MOF materials demonstrated potential for industrial H₂ 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.