Graphene can double desalination flux say MIT pair

The use of nanoporous graphene as a desalination material has received further research support, this time by two researchers at the Massachusetts Institute of Technology (MIT).

In their paper Water Desalination across Nanoporous Graphene published on 5 June 2012 in Nano Letters, the American Chemical Society journal, PhD candidate David Cohen-Tanugi and Professor Jeffery C Grossman claim that their results indicate that the water permeability of nanoporous graphene is several orders of magnitude higher than conventional reverse-osmosis membranes and that the material may have a valuable role to play in water purification.

The MIT pair state that nanometer-scale pores in single-layer freestanding graphene can effectively filter sodium chloride from water. Using classical molecular dynamics, they label desalination performance a function of pore size, chemical functionalization and applied pressure.

"Our results indicate that the membrane's ability to prevent the salt passage depends critically on pore diameter with adequately sized pores allowing for water flow while blocking ions," say the researchers. "Further, an investigation into the role of chemical functional groups bonded to the edges of graphene pores suggests that commonly occurring hydroxyl groups can roughly double the water flux thanks to their hydrophilic character."

The increase in water flux comes at the expense of less consistent salt-rejection performance, which the MIT pair attribute to the ability of hydroxyl functional groups to substitute for water molecules in the hydration shell of the ions.

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