Carbon is a pretty amazing element and pure carbon structures have a variety of uses and properties. From the incredible hardness of diamonds to the versatility of the graphite in our pencils, carbon is wonderfully diverse. Two-dimensional structures are also incredible and include things like graphene, carbon nanotubes, and fullerene, showcasing a range of useful properties. Now a new 2D carbon structure has been discovered.
It is called schwarzite and has been predicted and modeled for decades, but only now have researchers been able to produce it. And not on purpose. The new structure was created by scientists in South Korea and Japan by filling a particular type of silicon dioxide crystal (sand), known as a zeolite, with carbon. The creators were investigating whether these carbon-filled zeolites would have interesting properties.
An international team led by researchers at the University of California, Berkeley have proved that the three structures created by the Japanese-Korean team are indeed the long-sought-after schwarzites. Their findings are published in the Proceeding of the National Academy of Sciences.
The important property of a schwarzite is its curvature. Graphene is a flat sheet so it has zero curvature. Fullerenes, also known as buckyballs (from the full name buckminsterfullerene), are convex structures with positive curvature. Schwarzites are the first carbon structures with negative curvature and are shaped a bit like saddles. Schwarzites have the smallest area for their configuration.
The team constructed a computer simulation of the zeolite crystal and modeled how the carbon atoms could be arranged. The study showed that of the 200 zeolites created to date, only 15 can be used as a template to create schwarzite. But researchers think that there are over a million possible ways to make a zeolite, so there could be many more ways to make a schwarzite.
“These negatively-curved carbons have been very hard to synthesize on their own, but it turns out that you can grow the carbon film catalytically at the surface of a zeolite,” lead author Efrem Braun, from UC Berkeley, said in a statement. “But the schwarzites synthesized to date have been made by choosing zeolite templates through trial and error. We provide very simple instructions you can follow to rationally make schwarzites and we show that, by choosing the right zeolite, you can tune schwarzites to optimize the properties you want.”
Schwarzites are particularly suited to storing a large electric charge, making them efficient capacitors. They can also be constructed in ways that allow them to store other molecules, or even act as catalysts. Similarly to graphene, finding an efficient, high-quality, and cost-effective way to produce the structure will be key to its commercialization.