Ultrathin Magnesium-Ion Selective COF Membranes for Efficient Osmotic Power and Iontronic Logic Control

Magnesium ions (Mg²⁺), vital for biological signaling and energy regulation, remain challenging to selectively and efficiently transport using artificial membranes, which typically lack molecular recognition and confined ion channels. Here, we report a β-ketoenamine covalent organic framework (TAPA-TFP COF) membrane that achieves near-ideal Mg²⁺ selectivity (t₊ = 0.98) and ultrafast transport through ordered 13.6 Å nanochannels. Structural and molecular dynamics analyses reveal that the precisely arranged O/N coordination sites within the porous nanochannels partially strip the Mg²⁺ hydration shell, while C = O···H─O─H hydrogen-bond networks lower migration barriers, enabling high permeability. The ultrathin, large-area, and defect-free membrane delivers record osmotic power and current densities of 636.64 W m^-2 and 9213.3 A m^-2 under a 500-fold salinity gradient. Beyond efficient power generation, the Mg²⁺-selective nanochannels enable iontronic transistors, logic operations, and multimodal signal transduction, establishing a molecularly engineered porous platform that integrates ion-specific transport with energy conversion and information processing.