Graphene makes saltwater potable
New, less-expensive desalination system could help thirsty nations tap into an endless supply of sea water
Massachusetts Institute of
Technology researchers have come up with a new approach using a different kind
of filtration material: sheets of graphene, a one-atom-thick form of carbon,
which they say can be far more efficient and possibly less expensive than
existing desalination systems.
“There are not that many people working on desalination from a materials point of view,” says Jeffrey Grossman, senior author of a paper describing the new process in Nano Letters.
Grossman and student David Cohen-Tanugi, the lead author , aimed to “control the properties of the material down to the atomic level,” producing a graphene sheet perforated with precisely sized holes. They also added other elements to the material, causing the edges of these minuscule openings to interact chemically with water molecules – either repelling or attracting them.
“We were very pleasantly surprised” by how well graphene performed compared to existing systems in simulations, Grossman says.
A common method of desalination, called reverse osmosis, uses membranes to filter the salt from water. But these systems require extremely high pressure – and hence, energy use – to force water through the thick membranes, which are about a thousand times thicker than graphene. The new system operates at much lower pressure, and thus could purify water at far lower cost.
Thekeytothenewprocessisveryprecisecontrol 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.
Other research groups have worked to create pores in graphene, Cohen-Tanugi says, but at very different sizes and for very different purposes–forexample,makingmuchbiggerholestofilter large molecules like DNA, or to separate gases. The methods used for those processes were not precise enough to make the tiny holes needed for desalination, he says, but more advanced techniques might be suitable.
“There are not that many people working on desalination from a materials point of view,” says Jeffrey Grossman, senior author of a paper describing the new process in Nano Letters.
Grossman and student David Cohen-Tanugi, the lead author , aimed to “control the properties of the material down to the atomic level,” producing a graphene sheet perforated with precisely sized holes. They also added other elements to the material, causing the edges of these minuscule openings to interact chemically with water molecules – either repelling or attracting them.
“We were very pleasantly surprised” by how well graphene performed compared to existing systems in simulations, Grossman says.
A common method of desalination, called reverse osmosis, uses membranes to filter the salt from water. But these systems require extremely high pressure – and hence, energy use – to force water through the thick membranes, which are about a thousand times thicker than graphene. The new system operates at much lower pressure, and thus could purify water at far lower cost.
Thekeytothenewprocessisveryprecisecontrol 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.
Other research groups have worked to create pores in graphene, Cohen-Tanugi says, but at very different sizes and for very different purposes–forexample,makingmuchbiggerholestofilter large molecules like DNA, or to separate gases. The methods used for those processes were not precise enough to make the tiny holes needed for desalination, he says, but more advanced techniques might be suitable.
MM120706
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