Laboratory chemists at the US state of Texas’ Rice University, led by James Tour, have introduced a process in the science journal Nature by which almost any source of carbon can be turned into graphene flakes, the university said.
The gram-scale bottom-up flash graphene synthesis process is quick and cheap and can convert coal, food waste or plastic into graphene for a fraction of the cost of other bulk graphene-producing methods, said Tour.
The process produces ‘turbostratic’ graphene, which has misaligned layers that come apart in solution or upon blending in composites. This enables chemists to get each of the single-atomic layers to interact with a host composite.
The graphene can help facilitate a significant reduction in the environmental impact of concrete and other building materials. A concentration of as little as 0.1% of flash graphene in the cement used to bind concrete could reduce its environmental impact by a third.
“Graphene acts as a two-dimensional template and a reinforcing agent that controls cement hydration and subsequent strength development,” explained Rice University adjunct assistant professor of civil and environmental engineering, materials science and nanoengineering and coauthor Rouzbeh Shahsavari.
Graphene has been too expensive to use in these applications. The flash process will greatly lessen the price while helping to better manage waste, highlighted Tour.
“The world throws out 30% to 40% of all food because it goes bad, and plastic waste is of worldwide concern. We have proven that any solid carbon-based matter, including mixed plastic waste and rubber tyres, can be turned into graphene,” he said.
Flash graphene is made in ten milliseconds by heating carbon-containing materials to 3 000 Kelvin. The source material can be almost anything with carbon content. Food waste, plastic waste, petroleum coke, coal, wood clippings and biochar are prime candidates.
“With the present commercial price of graphene being $67 000 to $200 000 a ton, the prospects for this process look superb,” he added.
The process aligns strongly with Rice University’s recently announced Carbon Hub initiative to create a zero-emissions future that repurposes hydrocarbons from oil and gas to generate hydrogen gas and solid carbon with zero emission of carbon dioxide.
The flash graphene process can convert that solid carbon into graphene for concrete, asphalt, buildings, cars, clothing and more, Tour said.
Bulk composites of graphene with plastic, metals, plywood, concrete and other building materials would be a major market for flash graphene, according to the researchers, who are already testing graphene-enhanced concrete and plastic.
Used coffee grounds transform into pristine single-layer sheets of graphene, he added.
The flash Joule-based process takes place in a custom-designed reactor that heats material quickly and emits all noncarbon elements as gas. Elements like oxygen and nitrogen can be captured, owing to their value, Tour said.
The flash process produces very little excess heat, channelling almost all the energy into the target, despite the temperature being almost three times hotter than chemical vapour deposition furnaces. All the excess energy comes out as light and the process is clean because there are no solvents used, he said.
The process was developed by Rice University graduate student and lead author Duy Luong. His research was prompted by a science paper about flash Joule heating to make phase-changing nanoparticles of metals.
Luong did not expect to find graphene when he fired up the first small-scale device to find new phases of material, beginning with a sample of carbon black, but quickly realised the process produced nothing but high- quality graphene.