Sparkling water could be used to manufacture graphene
Image credit: University of Illinois Department of Mechanical Science and Engineering
A team of researchers at the University of Illinois have developed an environmentally friendly approach to isolating graphene, using carbonic acid in sparkling water to peel graphene away from the substrate on which it was formed.
Graphene is the world’s first 2D material: the thinnest in existence. It is often discussed as one of the most useful materials due to its flexibility, lightness, extreme strength and its excellent electrical and thermal conductivity. Potential applications vary from uses in tissue engineering to water filtration.
However, the material has yet to reach the exciting commercial applications that have been promised, and one factor holding back this revolution could be the difficulty of manufacturing pure sheets of graphene.
A popular school science experiment involves lifting a layer of pencil rubbings from paper with adhesive tape; a sheet of graphene. The standard method for producing the material is to deposit chemical vapour onto a substrate, normally copper foil. Both of these methods raise a significant problem: how can the atom-thick graphene be cleanly separated from its substrate?
Usually, this is attempted by dissolving the metal or through a delamination process that lifts layers apart. These methods require supportive coatings for the graphene, and tend to leave residue behind which – like gooey sticky-tape residue – requires tedious cleaning to be completely removed.
The scientists, who belong to the research group of Professor SungWoo Nam in the College of Engineering at Illinois, attempted an approach to delamination that used carbon dioxide to create a carbonic acid electrolyte, rather than using the harsh chemicals typically required, and using ethyl cellulose as the protective coating, a cheap polymer often used as a food additive.
“This not only makes our graphene transfer process more environmentally friendly, it is now also compatible with a variety of polymeric and soft biological materials such as common plastics and hydrogels that would otherwise not tolerate harsh solvents,” said Michael Cai Wang, the PhD student who led the research.
After the graphene is transferred, the carbonic acid completely evaporates as carbon dioxide gas and water, meaning that there is no need for further cleaning. By neatly delaminating the graphene from the foil substrate without harsh chemicals, they were able to reuse the undamaged substrate multiple times.
“We’re thus saving both water and time by eliminating the conventional need for the repetitive and tedious rinsing process,” said Professor Nam.
“I think scientifically what we are bringing to the community is to really motivate people to think about a cleaner way for making graphene,” he added. “We are trying to improve upon the well-established protocols so that industry can easily adopt our techniques. Because a lot of devices are contaminated by these previously used chemicals, it inevitably affects the property of graphene.”
Professor Nam and his colleagues hope that their work could inspire more novel applications for carbonic acid, which is otherwise a nuisance, resulting, for instance, in increasing ocean acidification.