Solvent‐Controlled Pathways Enable Structure‐Programmable Metal‐Organic Framework Membranes for Isomer Separation

ABSTRACT The separation of structurally similar aliphatic and aromatic isomers remains a critical industrial challenge, as their nearly identical sizes render conventional distillation highly energy‐intensive. Molecular‐sieving metal–organic framework (MOF) membranes offer an energy‐efficient alternative; however, reliably programming their growth pathways to achieve targeted pore architectures is difficult. Here, we report a solvent‐triggered pathway control strategy that directs distinct growth routes from a single vertically aligned Zn─Al layered double hydroxide (LDH) nanoarray template. In N , N ‐dimethylformamide (DMF), selective activation of LDH metal sites stabilizes the framework and guides a surface‐induced interstitial growth mechanism, yielding a dense Zn‐BODC membrane with ∼0.5 nm apertures for highly selective n‐hexane/2,3‐dimethylbutane (Hex/23DMB) separation. In water, rapid LDH dissolution triggers a complete template‐conversion pathway that replicates the honeycomb morphology, producing an Al‐BODC membrane with ∼0.7 nm pores capable of efficient para‐/ortho‐xylene (PX/OX) discrimination. These solvent‐defined pathways enable programmable microstructures and complementary separation performances. This work establishes a versatile platform for the rational design of ultramicroporous MOF membranes with tailored sieving properties for demanding isomer separations.