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Sunday, 2 February 2020

New method turns any carbon waste into graphene


Every day, several million tons of carbonaceous waste are thrown away to be stored in landfills and to be burned, or simply stored awaiting treatment. Despite the improvement of recycling techniques, a large part of this waste is definitively destroyed, an often polluting and costly process. But recently, a team of engineers has developed a new method, very inexpensive and very little polluting, allowing to quickly transform any carbonaceous waste - from banana peels to tires through wood - into graphene. This material, whose qualities are no longer to be demonstrated, can then be used in numerous applications.



The “graphene flash” technique, described in the journal Nature , is fast and inexpensive and consists of heating the waste to 2727 ° C. This breaks the carbon bonds inside the target materials, which are then reconstructed as graphene in a few milliseconds. Not only does this provide a means to use waste that would otherwise be thrown away, but it is an efficient and inexpensive way to produce graphene, which can then be used in different environmentally friendly ways.



"We have already proven that any solid carbon-based material, including mixed plastic waste and rubber tires, can be transformed into graphene," said chemist James Tour of Rice University. Existing graphene production processes produce either low quality graphene or high quality graphene in low volumes. Here, the scientists were able to develop a technique that makes it possible to obtain a decent quantity of good quality, in a shorter time and at a lower cost.

Graphene flash: the key role of temperature

At the center of the operation is a method known as Joule heating, where a rapid discharge of electricity is used to generate intense heat. It is a process that has already been used by engineers to create metallic nanoparticles.

(A, B, C): Structure and operation of the Joule effect heating device. (E): Different graphene structures synthesized from various sources. Credits: Duy X. Luong et al. 2020


The technique described could help convert materials such as food waste, plastic waste, petroleum coke, coal, scrap wood and biochar into precious graphene. It should also be relatively easy to scale up. Temperature is the key - it accelerates the evolution of carbon to its ground state of graphite, but also stops this evolution at exactly the right time to harvest high-quality graphene.

A fast, inexpensive and environmentally friendly recycling technique

If graphene can be generated cheaply, it means it can be used for more applications - to help in the production of cars or clothing, for example, or in cement to bond concrete (a responsible process about 8% of human-made CO2 each year).

Image of the Joule effect heater used for the synthesis of flash graphene. Credits: Rice University


“By reinforcing the concrete with graphene, we could use less concrete for construction, and it would be cheaper to manufacture and transport. Essentially, we are trapping greenhouse gases like carbon dioxide and methane that food waste would have emitted into landfills. We convert these carbons to graphene and add this graphene to the concrete, thereby reducing the amount of carbon dioxide generated in the manufacture of concrete. It's a win-win environmental scenario using graphene.”

No solvent or chemical additive is required for the process, and elements other than carbon are released as gases. In addition, the process produces very little excess heat and the containment device is cool to the touch within a few seconds. Graphene has already proven itself in a multitude of applications, covering electronics, manufacturing and cleaning of pollutants. Scientists can now make it cheaply, while reusing materials that would otherwise be wasted.




Bibliography:

Article: Gram-scale bottom-up flash graphene synthesis

Duy X. Luong, Ksenia V. Bets, Wala Ali Algozeeb, Michael G. Stanford, Carter Kittrell, Weiyin Chen, Rodrigo V. Salvatierra, Muqing Ren, Emily A. McHugh, Paul A. Advincula, Zhe Wang, Mahesh Bhatt, Hua Guo, Vladimir Mancevski, Rouzbeh Shahsavari, Boris I. Yakobson & James M. Tour

Nature volume 577, pages647–651(2020)

https://doi.org/10.1038/s41586-020-1938-0

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