Layered Double Hydroxide‐Assisted Fabrication of Prussian Blue Membranes for Precise Molecular Sieving

Abstract Prussian Blue (PB), which was first discovered as robust blue‐colored pigment in the year 1706, has shown promising prospects in disease treatment, energy conversion, water splitting, and sensing. Relying on the uniform 3.2 Å‐sized pore channels as well as high stability in aqueous environments, in this study, we pioneered in situ preparation of polycrystalline PB membranes to justify their dye rejection and metal ion discrimination ability in aqueous environments. Among various factors, the introduction of calcined NiFe layered double hydroxide buffer layers on porous α‐Al 2 O 3 substrates was found to play a paramount role in the formation of continuous polycrystalline PB membranes, thereby leading to excellent dye rejection efficiency (>99.0 %). Moreover, prepared PB membranes enabled discriminating different monovalent metal ions (e.g., Li + , Na + , and K + ) depending on their discrepancy in Stokes diameters, showing great promise for lithium extraction from smaller‐sized metal ions.