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Graphene-based water filtering systems are almost here

Posted October 23, 2012

Graphene production. Magnesium burning within dry ice. (Credit: workie/Flickr, CC BY 2.0)

Water filtration systems do not seem like a very widely-spread thing you could meet in the market, although we are all heavily dependent on these sophisticated devices. Removal of contaminants and other unnecessary substances from water – to make it fresh and drinkable – is not such an easy or cheap task. However, the next generation equipment for water filtering may employ graphene-based porous membranes. Quite a nice addition to already almost ‘miraculous’ set of graphene properties, isn’t it?

Graphene is typically regarded as one of the strongest and most resistant materials. Certainly, some defects may emerge during its industrial production, and these defects provide graphene with a property to pass relatively small molecules through them:

But the material may not be as impenetrable as scientists have thought. By engineering relatively large membranes from single sheets of graphene grown by chemical vapor deposition, researchers from MIT, Oak Ridge National Laboratory (ORNL) and elsewhere have found that the material bears intrinsic defects, or holes in its atom-sized armor. In experiments, the researchers found that small molecules like salts passed easily through a graphene membrane’s tiny pores, while larger molecules were unable to penetrate.

The researchers’ membrane, consisting of graphene on a polycarbonate track etch membrane (the graphene is the darker region i the center of the white film). (Credit: MIT)

The results, the researchers say, point not to a flaw in graphene, but to the possibility of promising applications, such as membranes that filter microscopic contaminants from water, or that separate specific types of molecules from biological samples. “No one has looked for holes in graphene before,” says Rohit Karnik, associate professor of mechanical engineering at MIT. “There’s a lot of chemical methods that can be used to modify these pores, so it’s a platform technology for a new class of membranes.”

<…> In particular, the team cast around for materials with two key attributes, high flux and tunability: that is, membranes that quickly filter fluids, but are also easily tailored to let certain molecules through while trapping others. The group settled on graphene <…>

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