Simple Methods for Producing Graphene Quantum Dots from Coal

Scientists at Rice University have found simple methods to reduce three kinds of coal into graphene quantum dots (GQDs) - microscopic discs of atom-thick graphene oxide that have applications in medical imaging, sensing, electronics, and photovoltaics. The GQDs were derived from bituminous coal, anthracite, and coke, a byproduct of oil refining. In quantum dots, band gaps - which determine how a semiconducting material carries an electric current - are responsible for their fluorescence and can be tuned by changing the dots' size. The new process allows a measure of control over their size, generally from 2 to 20 nanometers, depending on the source of the coal. There are many ways to make GQDs, but most are expensive and produce limited quantities. Last year, Rice University researchers found a way to make GQDs from relatively cheap carbon fiber, but coal promises greater quantities made even cheaper in just one chemical step. The fluorescent particles are water-soluble, and early tests have shown them to be nontoxic.