Self‐Assembled Nanoporous Metal–Organic Framework Monolayer Film for Osmotic Energy Harvesting

Abstract Osmotic energy represents a promising energy resource because it is sustainable and environmentally benign. Subnanoscale channels are considered as a competitive platform for generating this blue energy due to their highly selective and ultrafast ion transport. However, fabricating functional subnanochannels capable of high energy output remains challenging. Here, a heterogeneous subnanochannel membrane formed by coating a functionalized self‐assembled metal−organic framework (MOF) monolayer (SAMM) film on a porous anodic aluminum oxide membrane, is reported. The SAMM film, with a thickness of ≈160 nm, is fabricated by self‐assembly of poly(methyl methacrylate‐ co ‐vinylimidazole)‐modified UiO‐66‐NH 2 nanoparticles at the water−air interface. In the SAMM, imidazole and NH 2 groups provide abundant positive charges, while the angstrom‐scale windows act as ionic filters for selective screening of anions with different hydration diameters. As a result, the heterogeneous membrane exhibits excellent capacity for anion‐selective transport, which contributes to an optimal osmotic power of 6.76 W m −2 under a 100‐fold NaCl gradient, as well as a high Cl − /SO 4 2− selectivity of ≈42.2. Further, the output power is increased to 10.5 W m −2 by methylating imidazole moieties on the MOF surface. This work provides a facile and modular approach to fabricate subnanochannels for enabling highly selective and efficient osmotic energy conversion.