Lab+Life Scientist Mar 2015

Page 36

carbon chemistry

Researchers from the US and China have discovered a structural variant of carbon called ‘penta-graphene’ - a very thin sheet of pure carbon that resembles the pentagonal pattern of the tiles which pave the streets of Cairo.

U The authors of the paper include Puru Jena, a distinguished professor in VCU’s Department of Physics; Qian Wang, a professor at Peking University and an adjunct professor at VCU; and Jian Zhou, a postdoctoral researcher at VCU.

and mechanically stable, but also can withstand temperatures as high as 1000 K”, the authors said. “You know the saying ‘diamonds are forever’?”

nlike most forms of carbon, which

said senior author Puru Jena from VCU. “That’s

are made of hexagonal building blocks and sometimes

because it takes a lot of energy to convert diamond

interspersed with pentagons, carbon structures

back into graphite. This will be similar.”

composed only of pentagons were, until now,

Penta-graphene’s mechanical strength is derived

unknown. Writing in the journal Proceedings of the

from a rare property known as negative Poisson’s

National Academy of Sciences, the researchers ask,

ratio, said the researchers, as a result of its unique

“Is it possible to have materials made exclusively of

atomic configuration. The way the material stretches

carbon pentagons and if so will they be stable and have

is particularly unusual, with Wang noting, “If you

unusual properties?”

stretch graphene, it will expand along the direction

Qian Wang, a professor at Peking University

it is stretched but contract along the perpendicular

and an adjunct professor at Virginia Commonwealth

direction. However, if you stretch penta-graphene,

University (VCU), explained that she was dining

it will expand in both directions.”

in a restaurant with her husband when she noticed

And while graphene is a conductor of electricity,

artwork on the wall depicting pentagon tiles from

penta-graphene is a semiconductor. Jena explained,

the streets of Cairo.

“When you take graphene and roll it up, you make

“I took a picture and sent it to one of my students,

what is called a carbon nanotube, which can be

and said, ‘I think we can make this. It might be stable.

metallic or semiconducting. Penta-graphene, when

But you must check it carefully,’” she recalled. “He

you roll it up, will also make a nanotube, but it is

did, and it turned out that this structure is so beautiful

always semiconducting.” Although penta-graphene is currently only

yet also very simple.”

36 | LAB+LIFE SCIENTIST - March 2015

The researchers simulated the synthesis of

theoretical, Jena believes the eventual synthesis of

penta-graphene - a two-dimensional carbon allotrope

the material will “open up an entirely new branch of

composed entirely of pentagons - using computer

carbon science”. The versatility of the penta-graphene

modelling. According to their calculations, “the

and its derivatives is expected to have applications in

new carbon polymorph is not only dynamically

electronics, biomedicine, nanotechnology and more.

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New structural variant of carbon made of pentagons