Creating Sodium Ion Channels via <i>De Novo</i> Encapsulation of Ionophores for Enhanced Water Energy Harvesting

Biological ion channels achieve remarkable permselectivity and cation discrimination through the synergy of their intricate architectures and specialized ionophores within confined nanospaces, enabling efficient energy conversion. Emulating such selectivity in synthetic nanochannels, however, remains a persistent challenge. To address this, a novel host-guest assembly membrane is developed by incorporating sodium-selective ionophores into a β-ketoenamine-linked covalent organic framework (COF). This design confers exceptional permselectivity and Na⁺ selectivity, achieving Na⁺/K⁺ and Na⁺/Li⁺ selectivity ratios of 3.6 and 103, respectively, along with near-perfect Na⁺/Cl^- selectivity under a 0.5 M || 0.01 M salinity gradient. Notably, the membrane dynamically switches its permselectivity to favor anion transport in the presence of high-valent cations (e.g., Ca²⁺), overcoming limitations such as uphill cation diffusion and back currents observed in conventional cation-selective membranes. This adaptive behavior yields a 4.6-fold increase in output power density in Ca²⁺-rich environments. These findings advance the design of biomimetic nanochannels with unparalleled ion selectivity and enhanced energy conversion efficiency.