Biomimetic Two-Dimensional Vermiculite Nanofluidic Membranes for Stable Salinity-Gradient Energy Conversion.

Aligned ion transport in the nanofluidic membrane is promising for efficient salinity-gradient energy conversion, while remaining rather challenging due to relatively inadequate mass transport and long-time durability. In this work, wet-chemically exfoliated and negatively charged vermiculite lamellas are readily restacked into free-standing membranes with massive arrays of nanochannels and a three-dimensional interface. The resulting vermiculite nanofluidic membranes possess excellent stability against harsh conditions including a wide pH range and high temperature and exhibit a different ion transport behavior from the macroscopic one due to the surface-charge-governed conductivity. The ionic conductivity is several orders of magnitude higher than that of the native solution at low concentrations. Moreover, the negatively charged lamellas create a space charge zone, making the nanofluidic membrane capable of coupling surface charge and space charge in confinement for salinity-gradient energy conversion from seawater and freshwater. Compared with other layered materials, the vermiculite-derived membranes have distinct advantages such as low cost, facile fabrication, and high stability. This work provides a new idea for designing nanofluidic membranes from phyllosilicate minerals, which offers opportunities for manufacturing nanofluidic devices.