2D Chitin Sub-Nanosheets with Extreme Ion Transport for Nanofluidic Sensing.

Nanofluidic membranes possess unique ion-selective transport properties, offering considerable potential for energy harvesting and sensing applications. However, the scarcity of anion-selective membranes has significantly hindered progress in these fields. Herein, the energy disparities among chitin crystalline planes are exploited to selectively cleave the low-energy (020) plane, facilitating the directional exfoliation of Bouligand-structured chitin into 2D sub-nanosheets (CSs) with an average thickness of 0.7 nm and lateral dimensions of 50-100 nm. Simulations and experiments demonstrate that a reduction in thickness significantly enhances both the ion transport flux (1.53 times) and selectivity (1.14 times), which in turn boosts the power output density to 12.95 W m under a 50-fold salinity gradient surpassing all-existing biomass-based nanofluidic membranes (max. 2.87 W m) and the commercial benchmark (5.0 W m). Furthermore, the membranes' extreme ion management capabilities facilitate real-time nanofluidic sensing, as demonstrated in jellyfish cultivation monitoring. This study presents a cost-effective strategy for developing high-performance, positively-charged nanofluidic membranes with exceptional energy harvesting and sensing capabilities, laying the foundation for advanced energy and sensing technologies.