Graphyne, Cousin of Graphene, Has Been Made In Bulk At Last

Graphene, formed from hexagonal rings of carbon atoms, has been dubbed a “wonder material” since its invention 17 years ago. Its creation won the 2010 Nobel Prize for Physics, and dozens, perhaps hundreds, of applications are under investigation.

For at least sixty years, scientists imagined a related format for carbon atoms they called graphyne, and interest has risen since graphene’s production. However, attempts to make graphyne have produced microscopic quantities not even large enough to display large-scale behaviors.

An announcement in Nature Synthesis of a reliable path to making graphyne has changed that.

Carbon has an unmatched capacity to form the basis of complex molecules, binding both to itself and other elements. That’s why we (and every other life form we know) are built out of molecules with carbon scaffolds, even if we contain more oxygen and hydrogen atoms. Even pure carbon can arrange itself in very different ways – represented in nature by graphite, soot, and diamonds.

Alternative carbon structures – rare or non-existent in nature – include near-spherical or cylindrical fullerenes, whose accidental production won the 1996 Nobel Prize for Chemistry and are being studied as potential stealth bombers for cancer cells. More recently, graphene’s strength and electrical conductivity have made it a candidate for bulletproof vests and better batteries among many other possibilities.

Graphyne resembles graphene in more than in name – both are sheets of carbon a single atom thick. However, where graphene has a simple honeycomb structure formed of endlessly repeating hexagonal rings, graphyne is more complex. Rather than bordering directly on each other, the benzene rings are spaced further apart and joined by alkyne bonds, where two carbon atoms form a triple covalent bond (six electrons) to each other.

How graphyne is made from carbon-hydrogen rings. Image Credit: Hu et al/Nature Synthesis

Graphene conducts electrons exceptionally quickly, but does so in all directions, while graphyne’s conductivity is expected to be able to be controlled to go only in the desired direction. Theoretical models also suggest graphyne is capable of forming localized electric fields known as Dirac cones. The electrical effects these produce could be tweaked in ways that may make graphyne even more effective for transistors or solar cells than graphene is expected to be.

Nothing is useful if you can’t make it, however, and on those rocks hopes from graphyne have floundered until now. Dr Yiming Hu who recently graduated from the University of Colorado, Boulder, and co-authors have changed that using alkyne metathesis, a reaction that redistributes alkyne bonds. Alkyne metathesis is reversible, opening the way to much greater flexibility in synthesizing materials.

“The whole audience, the whole field, is really excited that this long-standing problem, or this imaginary material, is finally getting realized,” said Hu in a statement.

“There’s a pretty big difference [between graphene and graphyne] but in a good way,” Professor Wei Zhang of UC Boulder said, although so far those differences are largely based on theoretical modelling, rather than experimentation.

The process is still complex and expensive; the team is aiming to address both, and if they can’t, applications may be limited. In the meantime, however, the process described is good enough to produce quantities required for research on photographyne’s characteristics and potential uses can be explored.

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