Plasmonic Ion Diode Membrane (PIDM) for Enhanced Nanofluidic Ion Transport.

Efficient applications of nanofluidic devices are often limited by the insufficient ion permselectivity and inherent ion concentration polarization (ICP) phenomenon. In this work, a bio-inspired plasmonic ion diode membrane (PIDM) was designed and fabricated for enhanced ion transport and osmotic energy harvesting by integrating covalent organic frameworks (COFs) and three-dimensional Au nanoparticles (3D AuNPs) into anode aluminum oxide (AAO). Under light irradiation, localized surface plasmon resonance (LSPR) excitation of 3D AuNPs can release huge plasmonic heat and produce abundant hot charge carriers (hot electrons and holes) simultaneously. The former heats the solution and generates a thermal gradient for boosting ion flux, while the latter transfers to the COFs layer, increasing charge density for promoting ion permselectivity. Importantly, it has been found that different COFs with varied pore sizes and charges have an obvious influence on energy harvesting efficiency. Under the optimum condition, a high output power density of 65.7 W m in a 500-fold concentration gradient could be achieved. This work provides a practical and efficient way to boost ion transport and enhance osmotic energy conversion by utilizing the synergistic effect of plasmonics and ion diode (ID) property.