Yi Liu

Separation methods based on 2D interlayer galleries are currently gaining widespread attention. The potential of such galleries as high‐performance gas‐separation membranes is however still rarely explored. Besides, it is well recognized that gas permeance and separation factor are often inversely correlated in membrane‐based gas separation. Therefore, breaking this trade‐off becomes highly desirable. Here, the gas‐separation performance of a 2D laminated membrane was improved by its partial self‐conversion to metal–organic frameworks. A ZIF‐8‐ZnAl‐NO₃ layered double hydroxide (LDH) composite membrane was thus successfully prepared in one step by partial conversion of the ZnAl‐NO₃ LDH membrane, ultimately leading to a remarkably enhanced H₂/CH₄ separation factor and H₂ permeance.

Separation methods based on 2D interlayer galleries are currently gaining widespread attention. The potential of such galleries as high‐performance gas‐separation membranes is however still rarely explored. Besides, it is well recognized that gas permeance and separation factor are often inversely correlated in membrane‐based gas separation. Therefore, breaking this trade‐off becomes highly desirable. Here, the gas‐separation performance of a 2D laminated membrane was improved by its partial self‐conversion to metal–organic frameworks. A ZIF‐8‐ZnAl‐NO₃ layered double hydroxide (LDH) composite membrane was thus successfully prepared in one step by partial conversion of the ZnAl‐NO₃ LDH membrane, ultimately leading to a remarkably enhanced H₂/CH₄ separation factor and H₂ permeance.

We develop here a urea hydrolysis method to in situ prepare asymmetric ZnAl-CO₃ layered double hydroxide (LDH) buffer layers with various stable equilibrium morphology on porous Al₂O₃ substrates. In particular it is found that well-intergrown ZIF-8 membranes can be directly synthesized on the ZnAl-CO₃ LDH buffer layer-modified substrates, owing to the specific metal–imidazole interaction between ZnAl-CO₃ LDHs and ZIF-8. Other Zn-based MOF membranes, like ZIF-7 and ZIF-90, can also be synthesized with this method. Our finding demonstrates that LDH buffer layer represents a new concept for substrate modification.

Research on interlayer gallery-based gas and liquid separation has gained widespread attention. A series of layered materials like lamellar ZSM-5, graphene and its derivatives have been fabricated into membranes showing fascinating gas/liquid separation properties. Layered double hydroxides (LDHs) are prominent representatives of layered compounds composed of regularly arranged brucite-like 2D sheets. Here we successfully prepared well-intergrown NiAl–CO₃ LDH membranes in one step. Particularly it was found that CO₂ dissolved in the precursor solution exerted great influence on the microstructure of prepared membranes. Trace amounts of CO₂ in the precursor solution led to the formation of ab-oriented 0.6 μm thick LDH membranes, while randomly oriented 5 μm thick LDH membranes formed from CO₂-saturated precursor solutions. Both ab- & randomly oriented LDH membranes showed clear size-based selectivity and H₂ was found to preferentially permeate through the interlayer galleries. However, randomly oriented LDH membranes showed a much higher H₂ selectivity possibly due to the decreased density of mesoscopic defects. Furthermore, in addition to the NiAl–CO₃ LDH membrane, a compact and randomly oriented ZnAl–NO₃ LDH membrane with reasonable gas selectivity was successfully prepared here by proper optimization of the synthesis conditions.

MOF membranes have gained widespread attention due to their unprecedented gas separation performance. Relying on physical interactions, we successfully deposited MOF seeds on a substrate modified with a network of vertically aligned LDH walls before secondary growth of the MOF layer. ZIF-8 membranes thus prepared show considerable H₂ permeance with high H₂–CH₄ selectivity. This approach is in general suitable for the deposition of nanoparticles on solid surface and their subsequent growth into a dense layer.

This study demonstrates that the interlayer galleries of layered compounds can exhibit size selectivity. A compact NiAl-CO₃ layered double hydroxide membrane was prepared showing a selectivity of ∼80 for the H₂–CH₄ mixture. The use of the γ-Al₂O₃ modified α-Al₂O₃ substrate and CO₂-saturated water solvent was essential for high-quality membrane fabrication.