Professor James Tour, T.T. and W.F. Chao chair in chemistry at Rice University, has discovered simple methods to reduce three kinds of coal into graphene quantum dots (GQDs), microscopic discs of atom-thick graphene oxide that could be used in medical imaging, as well as sensing, electronic and photovoltaic applications.
Exploring coal’s potential
“We wanted to see what’s there in coal that might be interesting, so we put it through a very simple oxidation procedure,” Tour explained. That involved crushing the coal and bathing it in acid solutions to break the bonds that hold the tiny graphene domains together.
Another Rice chemist, Angel Martí, assistant professor of chemistry and bioengineering, then helped to characterise the product, finding that different types of coal produced different types of dots. GQDs were derived from bituminous coal, anthracite and coke. Bituminous coal produced GQDs between 2 and 4 nanometers wide; coke produced GQDs between 4 and 8 nanometers; and anthracite made stacked structures from 18 – 40 nanometers, with small round layers atop larger, thinner layers.
According to Tour, the dots are water-soluble and early tests have shown them to be nontoxic. That offers the promise that GQDs may serve as effective antioxidants, medical imaging could also benefit, as the dots show robust performance as fluorescent agents.
The promise of cheap GQDs
But it is the low cost of production that is the real draw. Existing methods of producing GQDs, which depend on graphite, are expensive and only result in very small quantities. “Graphite is US$ 2000/short t for the best there is, from the UK,” Tour said. “Cheaper graphite is US$ 800/short t from China. And coal is US$ 10 – US$ 60/short t.”
In contrast, coal offers the cheapest material available for producing GQDs: “Coal is the cheapest material you can get for producing GQDs, and we found we can get a 20% yield. So this discovery can really change the industry. It’s going to show the world that inside of coal are these very interesting structures that have real value.”
Adapted from press release by Jonathan Rowland
Read the article online at: https://www.worldcoal.com/coal/11122013/rice_university_scientists_discover_method_of_turning_coal_into_graphene_coalnews241/