Light-driven directional ion transport for enhanced osmotic energy harvesting

Abstract

Light-driven ion (proton) transport is a crucial process both for photosynthesis of green plants and solar energy harvesting of some archaea. Here, we describe that TiO2/C3N4 semiconductor heterojunction nanotube membrane can realize a similar light-driven directional ion transport performance as biological systems. This heterojunction system can be fabricated by two simple deposition steps. Under unilateral illumination, TiO2/C3N4 heterojunction nanotube membrane can generate a photocurrent of about 9 μA/cm2, corresponding to a pumping stream of ∼5500 ions per second per nanotube. By changing the position of TiO2 and C3N4, a reverse equivalent ionic current can also be realized. Directional transport of photo generated electrons and holes results in a transmembrane potential, which is the basis of the light-driven ion transport phenomenon. As a proof of concept, we also show that this system can be used for enhanced osmotic energy generation. The artificial light-driven ion transport system proposed here offers a further step forward on the roadmap for the development of ionic photoelectric conversion and their integration in other applications, e.g. water desalination.

Light-Driven Ion Transport in Nanofluidic Devices: Photochemical, Photoelectric, and Photothermal Effects

“…Xiao et al reported a C 3 N 4 /TiO 2 nanotube (CNTN) semiconductor heterojunction nanofluidic device that could realize a higher performance of light-driven directional ion transport than that of carbon nitride nanofluidics. 23 Under the same light illumination, the lightinduced ionic current could be enhanced to 9 μA/cm 2 , which could be ascribed to the more efficient photoinduced carrier separation.…”

“…[15][16][17][18][19][20] Light-driven ion transport is an interesting phenomenon occurring in certain nanofluidic devices based on their material attributes. 8,[21][22][23] In these systems, the consumption of solar energy moves ions from a low concentration to a high concentration to establish a chemical potential (active transport) or amplify ionic flow from a high concentration to a low concentration (passive transport). The active ion transport phenomenon is common in microorganisms or green plants that pump protons or ions across cell membranes, generating an osmotic and charge imbalance via solar energy consumption.…”

“…It is possible to integrate light-driven ion transport nanofluidic systems with other membrane-based systems to realize large-scale industrial applications, for example, light-enhanced osmosis energy harvesting. 23 These advantages equip light-driven ion transport nanofluidic systems with promising applications to conceive new types of ionic machines, separation and desalination membranes, and lightelectron energy conversion systems.…”

Nanofluidic osmotic power generators – advanced nanoporous membranes and nanochannels for blue energy harvesting

“…Similar strategies have been reported in 2D MXene membranes and TiO 2 /C 3 N 4 heterojunction nanotubes. 202,203 These examples illustrate the possibility to combine solar energy and SGE with a relatively simple strategy.…”

Bioinspired nanochannels based on polymeric membranes

“…The bio-light driven ion pump uses the concentration gradient of ions to create a membrane potential [23], and converts the energy stored in sunlight into an osmotic potential. The application of nanochannels to participate in the photoelectric conversion process, directly or indirectly, has received increasing attention [24,79,217,218 [79] used PSII complexes extracted from green plants and certain bacteria, the natural photoelectric conversion materials, as a "pump" to convert light into ion current (Fig. 13a).…”