Graphene and Carbon Nanotubes

We see a lot of headlines about the “miracle” properties of graphene and carbon nanotubes, but the stories underneath the headlines are either very vague or way too technical.

In plain English, what are graphene and carbon nanotubes all about?

caption — *Above, a single layer of carbon atoms as seen through a scanning tunneling microscope. Below, a model showing the honeycomb lattice structure of those atoms in a sheet of graphene.*

Graphene

Graphene is simply a two-dimensional sheet of carbon atoms, the thinnest material known.

Those carbon atoms bond very tightly, so graphene is also the strongest known material for its volume.

It also has excellent thermal and electrical conductivity.

Scientists have long theorized that the mineral graphite is made of graphene.

Efforts to produce graphene began in 1990 but weren’t very successful until 2004.

Andre Geim and Kostya Novoselov, of the University of Manchester won the Nobel Prize in Physics for peeling a single layer of graphene off bulk graphite with adhesive tape and then transferring it to a silicon wafer.

Why all the fuss about graphene? It’s highly reactive, which means it can be used in many ways. In addition, the two-dimensional structure enables the construction of any size of graphene molecule (think of a long sheet of cloth being measured out by a tailor and cut to size).

Ten years have passed since Geim and Novoselov’s discovery, but the global market for graphene is only $9 million, mainly in the fields of electronics, batteries, and composites.

It’s not easy or inexpensive to produce a single layer of atoms in commercial quantities. The two basic methods used to make graphene today are exfoliation (basically what Geim and Novoselov did with adhesive tape) and deposition of graphene on another crystal (a process called epitaxy).

*Touch screens, smart windows, flexible LCDs and OLEDs, and solar cells thanks to graphene. Source*

Commercial graphene comes in a variety of dry, oily, and aqueous forms. According to manufacturers, it can be used in advanced composites, coatings, lubricants, electronics, batteries, thermal applications, printing ink and printer construction, and films.

Graphene is also facing competition from MX2 materials that have the same strong crystalline structure and ability to conduct electricity but, unlike graphene, can be switched off and on.

Weird optical properties make gold nanoparticles appear pink or purple. Source — *Weird nanoparticle optical properties make colloidal gold appear pink or purple. Source*

Carbon nanotubes

Carbon nanotubes are nanoparticles, a class of materials that are 1 to 100 nanometers wide.

Humanity has had practical experience with nanoparticles for centuries without knowing how the desired properties they confer came about.

In 1857, Michael Faraday discovered that, by breaking the normally inert element gold down into tiny colloidal particles, it became chemically reactive and had unusual optical properties.

It wasn’t until the 1970s and 1980s that “ultrafine particles” were identified. These officially became “nanoparticles” in the 1990s.

Carbon nanotubes are part of the fullerene family of nanoparticles that was discovered in 1985. A fullerene is essentially any molecule of carbon other than diamond (I think) or a two-dimensional flat shape.

A carbon nanotube is basically a graphene sheet rolled up into a tube. They come as a single tube or as two or more tubes nested together.

You can control the nanotube’s property by changing its diameter and the specific angle rolled. Depending on the tube’s orientation, a carbon nanotube can be either metallic or semiconducting.

Carbon nanotubes have high surface area for other materials to bond with. They have the excellent electrical and thermal conductivity of graphene, as well as great strength from graphene’s carbon-carbon bonds.

Carbon nanotubes are not inexpensive, but they are easier to produce than graphene. In 2004, they had a $6 million market, mainly in electronics, composites, and industrial catalysts.

It remains to be seen if they will fulfill their early promise, in part because of growing concerns over possible health hazards.

Hazards

Research into hazards from graphene has shown mixed results.

Carbon nanotubes, on the other hand, may pose an inhalation occupational health hazard.

*Scanning tunneling microscopic image of a carbon nanotube. Source*

Research into carbon nanotube hazards began in 2007. Under certain conditions, experiments have shown that they can enter and kill human cells. Studies on animals have shown that carbon nanotubes cause inflammation, microscopic nodules, fibrosis, and lung changes.

The shape of carbon nanotubes is similar to asbestos fibers. While they haven’t yet been proven to cause mesothelioma, ongoing research thus far supports that possibility.

No other element bonds as strongly to itself as carbon does. Graphene comes from graphite, the stable mineral form of carbon at Earth’s surface. Sheets of graphene can be rolled up into nanotubes.

It is taking decades to understand and commercially develop graphene and carbon nanotubes, but this has often been true of very useful materials down through human history. In the future, both of these nanomaterials may fulfill their early promise.

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Note: I had to rely almost solely on Wikipedia articles for this post. It was either that or extremely technical information that I could make very little use of for a general article…even when I could understand it. It makes me wonder, how are we going to control science and technology that most of us cannot understand – hmm, material for another article!