“The earth harbors about 1.4 billion cubic kilometers of water. Unfortunately, the vast majority of that water comes from the sea and is not potable unless treated by expensive, energy-hungry desalination plants. Those problems stem largely from inefficiency in the way salt ions are separated from water molecules, and the solution, says a team of materials scientists from the Massachusetts Institute of Technology, lies in fundamentally revising that process.
“The predominant desalination method today–reverse osmosis (RO)–relies on polymer-based membranes to remove salt and requires great pressure to push water through a semipermeable film.The more pressure applied, the higher the cost. The M.I.T. researchers, led by Jeffrey Grossman andDavid Cohen-Tanugi, propose that films made of graphene could filter out salt without inhibiting the water flow as much. Graphene, a superstrong sheet of carbon that is only one atom thick, has mostly been seen as a material forimproving electronics and optical communications.
“Reverse osmosis requires less energy than other desalination approaches–such as thermal distillation–but graphene membranes containing nanoscale pores that are more permeable than the polymers currently used would further cut energy requirements, the researchers reported online last month in Nano Letters.
“The idea is to discriminate between water molecules and salt ions based on size. “Reverse osmosis uses size exclusion, except it excludes everything,” says Grossman, an associate professor of power engineering.
“A graphene membrane would provide well-defined channels that allow water molecules to flow through at lower pressures while blocking salt ions, Grossman says.”
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