NEWS OF THE WEEK
GRAPHENE DEFECTS HELP MOVE PROTONS MATERIALS: Atomic-scale imperfections act like a bucket line, passing protons through the material
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IKE AN ATOMIC-SCALE bucket brigade, molecu-
lar species residing at defects in graphene work together to shuttle protons through the ultrathin carbon film, according to a new study. The investigation surprisingly shows that single layers of graphene, on their own, can selectively transmit protons in water. The finding deepens understanding of transport properties of the atomically thin carbon material and may lead to improved proton-selective membranes, a critical component of fuel cells. In the ongoing push to explore graphene’s potential applications, several researchers have studied proton conduction through graphene. The results indicate that protons cannot pass through the material, unless researchers modify it with dopants, puncture it to form fine holes, or apply a voltage. The new study, which was conducted by a multi-institution team led by Franz M. Geiger of Northwestern University, shows that those procedures are not required to coax protons through graphene (Nat. Commun. 2015, DOI: 10.1038/ncomms7539). Rather, a small number of atomic-scale defects that form naturally during graphene synthesis cause the material to rapidly MATTHEW NEUROCK/UNIVERSITY OF MINNESOTA
Hydroxyl groups bonded to carbon atoms that form a tiny graphene defect pass protons in water from one OH group to another through a graphene film. O is red, H is white, C is gray, yellow marks proton starting position on a water molecule, and blue spheres indicate proton transfer route.
transmit aqueous protons through the carbon network. The team deposited a carefully characterized graphene film on a silica support and then added an aqueous solution. As they cycled the solution between low and high pH values, the team used a highly sensitive laser spectroscopy method to monitor protonation and deprotonation of silanol groups on the silica surface. When the solution pH was low, protons in solution moved through the graphene film to the silanol groups, and when the pH was high, protons traveled in the opposite direction. Through a combination of microscopy and other analyses, the group ruled out proton diffusion through pinhole defects and ensured that the film was not damaged by exposure to laser light and other probes. The analysis, coupled with computations, shows that graphene exhibits rare defects—holes—surrounded by six carbon atoms that are either terminated with three oxygen atoms or six OH groups. The terminating oxygen atoms prevent proton transfer. But the hydroxyl groups work like an old-time bucket brigade grabbing protons from water and passing them quickly from one OH group to another, thereby transporting protons through the graphene membrane. “The upshot is—for proton-separating membranes all you need is slightly imperfect single-layer graphene,” Geiger says. Relative to earlier investigations of graphene proton transport, “this paper reports important technical and scientific advances,” says Mischa Bonn of the Max Planck Institute for Polymer Research, in Germany. The study, he says, provides insights into the proton conduction mechanism and describes a relay for protons that’s inaccessible to atoms and molecules. Chemistry professor James T. (Casey) Hynes of the University of Colorado, Boulder, remarks that the study adds to the list of known proton relay chains, such as ones through proteins or at ice surfaces in the stratosphere. “This addition to the list, in an utterly hydrophobic environment, is a quite striking and pleasant surprise.”—MITCH JACOBY
CORPORATE STRATEGY DSM to forsake commodities with caprolactam deal Continuing to move away from its industrial chemical roots, the Dutch firm DSM has signed a deal to put its polymer intermediates and composite resins businesses into a new company run by the investment firm CVC Capital Partners. The yet-to-be-named firm will be owned 65% by CVC and 35% by DSM. It will have annual sales of more than $2 billion and close to 2,000 employees. DSM expects a net of up to $370 million from the deal. More than 60% of the new firm’s sales will be of caprolactam, a nylon 6 raw
material that DSM has made for 60-plus years. Its other products will be the intermediate acrylonitrile and polymers such as unsaturated polyester and vinyl esters used to make fiberglass composites. DSM put the businesses up for sale last November, saying they no longer fit its focus on nutritional ingredients and performance materials. However, DSM will continue to buy caprolactam from the new company for use by the performance materials business, one of the world’s largest producers of nylon 6. Last summer, Third Point, an activist
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investment firm that owns a stake in DSM, suggested that the Dutch company should also exit performance materials and become a pure-play supplier of nutritional ingredients. DSM CEO Feike Sijbesma has resisted the argument. For DSM, the strategy of putting an unwanted business into a joint venture is tried and true. Almost exactly a year ago it completed the formation of DPx Holdings, a company that combines DSM’s pharmaceutical chemicals business with the drug services firm Patheon. DSM owns 49% of DPx.—MICHAEL MCCOY
