Saturday, December 7, 2013

Quantum dots from... coal?

For those not following along with recent physics and materials science, the newest wonder material is graphene, made of two-dimensional sheets of carbon just one atom thick. The 2010 Nobel Prize in physics was awarded for its discovery. Here's a short primer on why it's cool because of its amazing strength, conductivity and flexibility. To be honest, there's a long road ahead in making practical devices from the stuff -- this article in Nature from a couple weeks ago surveyed the promise and obstacles -- but the potential is huge.

Now, how about this for irony: a paper just out in Nature Communications shows that graphene quantum dots can be made in a very easy one-step process from ordinary coal. A quantum dot is like an artificial atom, and can be engineered to absorb/emit light at precise frequencies. Isn't it ironic that the cheap stuff we're burning all over the globe just for crude energy may be a great source for one of the most amazing materials we've ever discovered? Here's the abstract of the paper:
Coal is the most abundant and readily combustible energy resource being used worldwide. However, its structural characteristic creates a perception that coal is only useful for producing energy via burning. Here we report a facile approach to synthesize tunable graphene quantum dots from various types of coal, and establish that the unique coal structure has an advantage over pure sp2-carbon allotropes for producing quantum dots. The crystalline carbon within the coal structure is easier to oxidatively displace than when pure sp2-carbon structures are used, resulting in nanometre-sized graphene quantum dots with amorphous carbon addends on the edges. The synthesized graphene quantum dots, produced in up to 20% isolated yield from coal, are soluble and fluorescent in aqueous solution, providing promise for applications in areas such as bioimaging, biomedicine, photovoltaics and optoelectronics, in addition to being inexpensive additives for structural composites.

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