The Right Chemistry: Graphene is a remarkable material

Sir Andre Geim, professor of physics at the University of Manchester, has the distinction of being the only person to have been awarded both a Nobel and an Ig Nobel Prize. The Nobel represents the pinnacle of scientific achievement, while the Ig Nobel, organized by the humour magazine Annals of Improbable Research, aims to “honour achievements that first make people laugh, and then make them think.”

Geim received the 2000 Ig Nobel in physics for levitating a small frog with a powerful magnet and shared the 2010 Nobel Prize in physics with Sir Konstantin Novoselov for isolating “graphene,” a remarkable material that is thinner, stronger, more flexible and a better conductor of heat and electricity than any known substance.

To be sure, Geim and Novoselov did not “discover” graphene. Their Nobel citation reads “for ground-breaking experiments regarding the two-dimensional material graphene.” Those ground-breaking experiments began with a piece of graphite, some Scotch tape and an understanding that graphite is composed of planes of carbon atoms, each one bonded to three neighbours, 120 degrees apart, in a “chicken wire”-like lattice. The planes can slide relative to each other, which explains why graphite is an excellent lubricant. An analogy would be a deck of cards, with each card representing a flat layer of carbon atoms. “Graphene” is the term for one such layer.

Now imagine using a piece of tape to remove one card from the top of the deck. This is just what Geim and Novoselov did with their piece of graphite and Scotch tape. Then they stuck the tape on a silicon substrate and removed it to leave a one atom-thick sheet of graphene behind. Anyone can mimic this experiment using tape and the lead of a pencil which is actually made of graphite. Make a mark on paper and apply a piece of tape on top. When the tape is pulled off, some of the graphite will have transferred to it. Take another piece of tape and stick it over the smudge on the first one and pull it off. Some graphite will have transferred to the second tape. Imagine repeating this process until you only have one layer of graphite left. You have just made graphene! But you are not the first to have made it.

In 1859, English chemist Benjamin Collins Brodie treated graphite with a strong acid and observed a suspension of tiny crystals. Not knowing anything about the atomic structure of graphite at the time, he thought he made a novel form of carbon. Actually, he had made graphene oxide, a graphene sheet with some oxygen atoms attached to it. Without realizing it, he had pioneered graphene research! The theoretical foundations for understanding the structure of graphene were laid in a 1947 paper by McGill University physics professor Philip Wallace who was studying graphite, which at the time was of great interest because of its role in controlling the flow of neutrons in nuclear reactions.

Following up on Brodie’s work, in 1962, German chemistry professor Hanns-Peter Boehm treated oxidized graphite with an alkaline solution, and using an electron microscope identified what he suggested was “probably a single carbon honeycomb plane of the graphite lattice.” This set the stage for Geim and Novoselov’s isolation of pure graphene.

While the Scotch tape method can yield tiny amounts of graphene suitable for studying its properties, it is not amenable to the synthesis of large quantities. Excited by the material’s potential uses, chemists and physicists all over the world were soon cranking out publications about graphene and various methods for producing significant amounts were discovered. Exposing methane gas to a super-heated sheet of copper results in graphene deposited on the copper, and using graphite as an electrode in an electrolysis reaction leads to tiny flakes of graphene being stripped off. Ultrasound and microwaves can also be used to “exfoliate” graphite to yield graphene.

Now that graphene can be made, the question is what to do with it. Ultra-long-life batteries, bendable computer screens, water desalination filters, improved solar cells and superfast microcomputers are in the offing. So far, though, the only significant commercial applications have involved blending graphene with other materials to make stronger tennis racquets, hockey sticks and tires.

However, with the outbreak of COVID-19, another use has emerged. Several types of masks that incorporate some form of graphene have appeared. In one variety, graphene is generated by exposing the non-woven polypropylene layer of a surgical mask to a laser beam. This results in an improved repelling of virus-bearing droplets and allows for quick sterilization of the mask by exposing it to sunlight. Another mask includes a layer of graphene oxide that has potent antiviral properties because it can physically sheer the lipid outer-coating of a virus rendering it harmless.

This then brings up the question of whether such masks are harmless to the wearer. Can they release tiny particles of graphene that may be harmful if inhaled? Health Canada believes that is a possibility, at least with one type of mask that has been distributed to schools and daycare centres. However, without details of Health Canada’s findings, it is not possible for me to evaluate the risks.

Certainly inhalation of any particulate matter, especially smaller than five nanometres, can cause problems since on this “nano” scale, effects that might not be predicted based on bulk properties, such as triggering of an inflammatory response, may emerge. Consider, though, that there are many forms of graphene and of graphene oxide with different potential toxic effects.

For now, it is appropriate to follow Health Canada’s advice and avoid the masks in question, but let’s not throw the baby out with the bath water. Indeed, if the movie The Graduate were remade today, the word whispered into young Benjamin’s ear could well be “graphene” instead of “plastics.” The material’s potential is exciting, but light remains to be cast on the shadow of toxicity.


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