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Safe, Economical Method Devised to Make Graphene

Eucalyptus trees

Eucalyptus trees (ekaterinvor, Pixabay)

25 June 2019. Researchers in Australia and India developed a safer and much less costly process for synthesizing the super-material graphene using an extract from eucalyptus bark. The team from Royal Melbourne Institute of Technology in Australia and India’s National Institute of Technology in Warangal describe the process in the 13 June issue of the journal ACS Sustainable Chemistry & Engineering (paid subscription required).

Graphene is closely related to graphite like that used in pencils. The material is very light, strong, chemically stable, and only one atom in thickness, arrayed in a hexagonal pattern. Graphene can conduct both heat and electricity, with potential applications in electronics, energy, and health care. In 2010, two researchers at University of Manchester in the U.K. received the Nobel Prize in physics for their discoveries on graphene.

A continuing drawback with graphene, however, is the unsustainable process for producing the material. A widely used method synthesizes graphene from graphene oxide, which the researchers say relies on harmful chemical reagents to transform the flakes of graphene oxide into graphene sheets. The team — led by Suresh Bhargava, director of RMIT’s Centre for Advanced Materials and Industrial Chemistry, and National Institute of Technology chemistry professor Vishnu Shanker — is seeking a more sustainable and economical method for synthesizing graphene, while retaining the properties that makes it attractive for so many applications.

The researchers found their solution in the bark of the eucalyptus tree, also known as gum tree. Eucalyptus is a native and abundant plant species in Australia, which grows quickly and with evidence the trees can be irrigated with wastewater rather than fresh water. In this case, the researchers use a chemical extracted from eucalyptus bark containing polyphenols, chemicals found in plants with anti-oxidant properties.

The team uses polyphenol compounds from ground-up eucalyptus bark to separate graphene from graphene oxide flakes, in a water-based medium under reflux conditions, where reactants are heated, with vapors cooled into liquids through condensation. The result, say the authors, is 1 to 4 layers of stable, homogeneous graphene.

The researchers tested their eucalyptus polyphenol-produced graphene in a supercapacitor device, a type of energy storage that employs a static charge rather than the electrochemical reactions in batteries. Supercapacitors are used for energy storage that needs fast charge-discharge cycles. The team says their supercapacitor performed as well as a similar device made with conventional graphene, including charge–discharge rates and energy density.

But a key added benefit of this process is its low cost. In an RMIT statement, Bhargava calculates graphene made with eucalyptus polyphenols can be made at a cost of $US 0.50 per gram, compared to $100.00 a gram with conventional methods. “Our approach,” notes Bhargava, “could bring down the cost of making graphene from around $US 100.00 per gram to just 50 cents, increasing its availability to industries globally and enabling the development of an array of vital new technologies.”

Bhargava’s calculations may be due to the abundance of eucalyptus in Australia, but it grows as well in parts of the U.S., where in some locations at least, the trees are considered a nuisance.

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