Using neutron spectroscopy at multiple facilities, and first-principles calculations, the group were able to investigate the mechanism of water transport within the carbon nitride layers. Their results indicate that carbon nitride could be useful for developing high-performance membranes for application in water filtration devices and fuel cells.
A challenge when designing membrane structures for these applications is identifying materials that efficiently and selectively transport molecular water. This occurs frequently in biological systems, as cells maintain their internal hydration levels using aquaporins, which form tube-like structures made of proteins within the phospholipid bilayer of the cell wall.
The way the water molecules travel in single file along these protein tubes was used as inspiration for this study. The researchers recreated the structure of the aquaporin channels using stacked layers of the graphene-like compound carbon nitride.
The study, published in Science Advances, used neutron spectroscopy instruments at several facilities to achieve the energy resolutions needed to probe the different relaxation processes. Using Osiris at ISIS, as well as instruments at Institut Laue-Langevin, France, and the National Institute of Standards and Technology, USA, they were able to untangle the various contributions to the water dynamics over time scales extending from a few tens of picoseconds to several nanoseconds.
To supplement their neutron experiments, the group did extensive density functional theory (DFT) calculations to model the behaviour of the water in the channels, using their experimental results to verify their calculations. They found that the water molecules inside the channels undergo a series of interactions with the exposed ─N═ and ─NH═ species that replicates those seen in the biological aquaporin channels.
Further research is needed to investigate the behaviour of ions and other molecular species with these membranes, to determine the selectivity of the pores for water, but this ultrafast water transport indicates that these materials are excellent candidates for future membrane systems.
The full paper can be found at DOI: 10.1126/sciadv.abb6011