Researchers at the Oak Ridge National Laboratory, New Mexico State University and the University of Tennessee demonstrated the first experimental evidence of the use of single-layer porous graphene as a desalination membrane in 2015. Further recent and positive developments on the potential for desalination of seawater using graphene oxide membranes has been conducted by researchers at the University of Manchester.
As stated in the publication by US researchers, the resulting porous graphene membrane exhibited high rejection of salt ions and rapid water transport, thus functioning as an efficient water desalination membrane. Salt rejection selectivity of nearly 100% and exceptionally high water fluxes were measured using saturated water vapor as a driving force. In the experiment, the graphene was in direct contact with the water and the total driving pressure across the graphene membrane, which was provided by gravity and the vapor pressure of water at 40 °C, was estimated to be approximately 8 kPa.
The US authors also stated that based on the estimated density of nanopores, the estimated water flux through a single nanopore exceeds the flux through aquaporin channels by three orders of magnitude. However, no direct reference to water flux through aquaporin channels was provided in the publication, which is important to note since aquaporin reverse osmosis membranes are currently being developed for desalination of brackish waters and seawater.
UK researchers have shown that graphene oxide membranes show exceptional molecular permeation properties, with promise for many applications. However, their use in ion sieving and desalination technologies is limited by a permeation cut-off, which is larger than the diameters of hydrated ions of common salts. The cut-off is determined by the interlayer spacing swell in water.
However, the UK based researchers have determined how to control the interlayer spacing by physical confinement in order to achieve accurate and tunable ion sieving, which provides a sieve size smaller than the diameters of hydrated ions. Building on these findings, the UK researchers demonstrate a simple scalable method to obtain graphene-based membranes with limited swelling, which exhibit 97% rejection for NaCl.
Interesting times ahead!