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Plasma gun sprays out high-quality graphene

The fast, low-cost method splits graphite particles into graphene flakes, showing promise for mass production

by Prachi Patel, special to C&EN
February 12, 2021

Micrograph of a thin graphene flake sitting on a holey carbon framework shown with a 1 micrometer scale bar.
Credit: ACS Nano
Scanning electron micrograph shows a flake of graphene deposited onto a carbon grid.

Graphene has slowly made its way into sports gear, anticorrosion coatings, and even fabric face masks. But widespread use of the strong, conductive material in electronics, energy storage, and medical devices hinges on making high-quality graphene affordably and at large scale. Researchers now report an ultrafast way to peel graphene flakes a few atoms thick from graphite using a high-temperature plasma spray process (ACS Nano 2021, DOI: 10.1021/acsnano.0c09451).

The winners of the 2010 Nobel Prize in Physics first lifted monolayers of carbon atoms from graphite, the stuff of pencil lead, using ordinary sticky tape. That slow, painstaking method gives the highest quality graphene. Other exfoliation techniques yield very small amounts of graphene, and the material can have defects. Chemical vapor deposition (CVD), which grows materials from the bottom up, is now the leading method to make large amounts of graphene. But it requires multiple steps and remains expensive.

Photo of five 100 milliliter borosilicate bottles with blue caps filled with a black powder.
Credit: ACS Nano
Graphite can be split into high-quality graphene (black powder in bottles) with a plasma spray technique used to make ceramic coatings.

Anup Kumar Keshri, a materials scientist and engineer at the Indian Institute of Technology Patna, and his team made graphene using plasma spraying, a well-established technique for depositing metal or ceramic coatings. The method involves melting powdered coating materials in a jet of plasma—a high-temperature gas of ions—and spraying them on a surface.

The engineers loaded graphite particles in a plasma spray gun. The thermal shock from the 3,000 K temperature and the turbulent eddies in the resulting plume rip apart the graphite into graphene flakes. The researchers collected the sprayed powder, put it in deionized water, and spun it in a centrifuge to remove unexfoliated clumps of graphite.

Analysis with a variety of microscopy and spectroscopy methods showed that the graphene flakes were up to 3 µm in diameter, with 85% being a single atomic layer and the rest having a few layers. The material was free of defects and had a high carbon-to-oxygen ratio of 21, comparable to graphene made using CVD—both of which are signs of good quality. Films made with the graphene flakes were strong and had a lower electrical resistance than films prepared using graphene made with other exfoliation techniques.

The simple new method does not require any solvents, intercalants, or purification steps, Keshri says. It yields 48 g of graphene in 1 h and should be easy to scale up. The cost of the lab-made graphene is $1.12 per gram, which “is competitive or even lower than commercially available graphene,” he adds, and it should go down further when mass-produced.

Cecilia Mattevi, a materials scientist at Imperial College London, says that while the quality of the reported graphene looks promising, it will still have to be benchmarked in demonstrated applications against graphene produced traditionally via CVD. The strength and novelty of this approach, though, is “the high selectivity of monolayer graphene and the fast production rate in a nearly one-step process, which can enable large-scale production.”

The use of easily available industrial equipment and the quality of graphene produced stand out to James M. Tour, a chemist at Rice University. One downside is that graphite feedstock can be expensive, but still, “this is exciting, and I predict it will be industrialized,” he says.


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