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| Image Source: David Cohen-Tanugi |
| MIT researchers have invented a new kind of filtration material for desalination using sheets of graphene, the one-atom-thick form of the element carbon, which they say can be far more efficient and possibly less expensive than existing desalination systems. |
The filtering properties of graphene are a hot new topic of research and now Jeffrey Grossman, the Carl Richard Soderberg Associate Professor of Power Engineering in MIT’s Department of Materials Science and Engineering along with the graduate student David Cohen-Tanugi added other elements to the material to cause the edges of these holes to chemically interact with water molecules.
This makes them either they repel them or attract them. They found out that methods like chemical etching and self-assembling systems are suitable to make precise holes in graphene.
The research is published in the journal Nano Letters.
“We were very pleasantly surprised” by how well graphene performed compared to existing systems in computer simulations, Grossman says.
Another common method of desalination, called reverse osmosis, uses membranes to filter the salt from the water. These systems require extremely high pressure — and large energy resources — to force water through the thick membranes, which are about a thousand times thicker than graphene. The new graphene system operates at much lower pressure, and thus could purify water at far lower cost, the MIT researchers say.
Reverse osmosis has been used for decades however, “really basic mechanisms of separating salt from water are not well understood, and they are very complex,” Cohen-Tanugi says, adding that it’s very difficult to do experiments at the scale of individual molecules and ions. But the new graphene-based system, he says, works “hundreds of times faster than current techniques, with the same pressure” — or, alternatively, the system could run at similar rates to present systems, but with lower pressure.
The new process is very precise allows for control over the size of the holes in the graphene sheet. “There’s a sweet spot, but it’s very small,” Grossman says — between pores so large that salt could pass through and ones so small that water molecules would be blocked. The ideal size is just about one nanometer, or one billionth of a meter, he says. If the holes are just a bit smaller — 0.7 nanometers — the water won’t flow through at all.
For now, Grossman and Cohen-Tanugi have been doing computer simulations of the process to determine its optimal characteristics. “We will begin working on prototypes this summer,” Grossman says.
SOURCE MIT News
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