Engineering highly efficient Li⁺ responsive nanochannels via host-guest interaction and photochemistry regulation

Artificial nanochannels have seen great progress in energy storage, molecular filters, nanofluidic diodes, and biosensors. Precisely recognizing and transporting molecules or ions underpin the basis of artificial nanochannels. Here, we report highly efficient Li⁺ responsive nanochannels by design of functionalized porous anodic aluminum oxide (AAO) membranes. The 12-crown-4 unit was tethered to the synthesized spiropyran molecule, creating a smart Li⁺ responsive element, photochromic crowned spiropyran (CE-SP). The crown unit can specifically bind with Li⁺ while exempting the harassment of other metallic cations; and importantly, the spiropyran moiety possesses reversible photochemistry response, adding the flexibility to regulate ion transport behaviors. Upon the ultraviolet light stimulus, hydrophobic CE-SP molecules transform to positively charged crowned merocyanine (CE-MC), which can further convert to oxygen-negative ions in weak alkaline environment, thereby forming O^--Li⁺ interaction. Such structural evolutions enable to deftly tune the surface charge and wettability of the nanochannels, and thus ingeniously manipulate Li⁺ recognition profiled by ionic current signal. Moreover, electrically-driven release of the captured Li⁺ can be realized in an amiable condition, showing controllable capture-to-release ability. Finite element simulation unveils the fundamental mechanisms of ion transport pertaining to Li⁺ recognition events in the nanoconfinement. This work thus paves a way to construct high-performance Li⁺-selective nanodevice, and holds promise for Li⁺-related electrochemistry energy research.