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Researchers streamline control over coal-based graphene

Posted: 20 Mar 2015     Print Version  Bookmark and Share

Keywords:Rice University  graphene  band gap  coal  quantum dot 

Rice University scientists have made significant headway in the field of graphene research. According to Rice University lab chemist James Tour, graphene quantum dots made from coal can be engineered for specific semiconducting properties in either of two single-step processes.

In a recent study by the American Chemical Society journal Applied Materials & Interfaces, Tour and colleagues demonstrated fine control over the graphene oxide dots' size-dependent band gap, the property that makes them semiconductors. Quantum dots are semiconducting materials that are small enough to exhibit quantum mechanical properties that only appear at the nanoscale.

Tour's group found they could produce quantum dots with specific semiconducting properties by sorting them through ultrafiltration, a method commonly used in municipal and industrial water filtration and in food production.

Graphene quantum dots fluoresce in different colours

Vials hold solutions with graphene quantum dots that fluoresce in different colours depending on the dots' size. Techniques to produce the dots in specific sizes using coal as a source were developed at Rice University. (Credit: Tour Group/Rice University)

The other single-step process involved direct control of the reaction temperature in the oxidation process that reduced coal to quantum dots. The researchers found hotter temperatures produced smaller dots, which had different semiconducting properties.

Tour said graphene quantum dots may prove highly efficient in applications ranging from medical imaging to additions to fabrics and upholstery for brighter and longer-lasting colours. "Quantum dots generally cost about $1 million per kilogram and we can now make them in an inexpensive reaction between coal and acid, followed by separation. And the coal is less than $100 per ton."

Quantum dots

Rice University scientists have produced graphene quantum dots produced from coal with tuned band gaps and photoluminescent properties. These quantum dots, seen with an electron microscope, average 70nm in diameter. (Credit: Tour Group/Rice University)

The dots in these experiments all come from treatment of anthracite, a kind of coal. The processes produce batches in specific sizes between 4.5nm and 70nm in diameter.

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