Surfactant-Assisted Sulfonated Covalent Organic Nanosheets: Extrinsic Charge for Improved Ion Transport and Salinity-Gradient Energy Harvesting.

Charge-governed ion transport is the vital property of nanofluidic channels for salinity-gradient energy harvesting and other electrochemical energy conversion technologies. 2D nanofluidic channels constructed by nanosheets exhibit great superiority in ion selectivity, but a high ion transport rate remains challenging due to the insufficiency of intrinsic surface charge density in nanoconfinement. Herein, extrinsic surface charge into nanofluidic channels composed of surfactant-assisted sulfonated covalent organic nanosheets (SCONs), which enable tunable ion transport behaviors, is demonstrated. The polar moiety of surfactant is embedded in SCONs to adjust in-plane surface charges, and the aggregation of nonpolar moiety results in the sol-to-gel transformation of SCON solution for membrane fabrication. The combination endows SCON/surfactant membranes with considerable water-resistance, and the designable extrinsic charges promise fast ion transport and high ion selectivity. Additionally, the SCON/surfactant membrane, serving as a power generator, exhibits huge potential in harvesting salinity-gradient energy where corresponding output power density can reach up to 9.08 W m-2 under a 50-fold salinity gradient (0.5 m NaCl|0.01 m NaCl). The approach to extrinsic surface charge provides new and promising insight into regulating ion transport behaviors.