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Rock Doc: Engineering on a tiny scale hopefully will pay off big later

Mon., Jan. 7, 2013

One of the most exciting frontiers of modern science is “nano” or tiny-scale technology. Recently some interesting progress was announced about micro-engineering on the nano-scale that could have useful applications. Here’s the story and the background needed to understand it:

The solid materials around us differ from each other not just in terms of what they are made of, but how the atoms that compose them are bound together. One example of this fact revolves around the carbon atom. Diamond is made of carbon atoms with strong bonds to other carbon atoms that reach out in three dimensions. Diamond is very hard because of the strength of those bonds reaching out in regular ways to all directions.

Graphite is the material found in the center of pencils. (Some people call what you write with “lead,” but that’s misleading – there is no lead involved. That’s right, you won’t get lead poisoning by jamming yourself with pencil “lead,” no matter what your friends told you in grade school.) Graphite is made of carbon atoms, just like diamond. But in graphite the carbon is bound together in flat, six-sided hexagons in little groups of sheets. The sheets are pretty sturdy but they are bound together only loosely, which is why pencils easily make marks on paper – you tear off groups of sheets as you drag the pencil across paper. So although both diamond and graphite are made of the same stuff, they have very different properties because of the bonds that hold the carbon atoms together.

Here’s where it gets more interesting. Scientists can now produce a single layer of graphite molecules, bound together in hexagonal structures a bit like chicken wire. That accomplishment was good enough to win the 2010 Nobel Prize in physics for Andre K. Geim and Konstantin Novoselov. The single layer of graphite is called graphene. It’s essentially a two-dimensional crystal.

Recently scientists at the University of Colorado at Boulder announced progress in experiments with graphene. Professors Scott Bunch and John Pellegrino and their students created nanoscale pores in the graphene sheets using ultraviolet light to “etch” the material. They then measured the permeability of different gases through the ultra-thin material. Their experiments used natural gas, which chemists call methane, carbon dioxide, nitrogen and others.

What’s impressive is that the graphene could separate certain gases like a sieve – amazing to think about because the gas molecules have diameters measured in terms of billionths of a meter. We are talking one tiny-scale sieve!

And the sieve is stronger than one might think.

“It is the thinnest and strongest material in the world,” Bunch said in a University of Colorado press release.

We may be able to use graphene as a separation membrane. But there are some challenges to first overcome, like scaling the work up to create graphene membranes that are big enough for potential industrial use. Still, if the work moves forward we may have found a way to separate out carbon dioxide – a greenhouse gas – from power-plant emissions.

Not bad for a tiny piece of work.

E. Kirsten Peters, a native of the rural Northwest, was trained as a geologist at Princeton and Harvard. This column is a service of the College of Agricultural, Human and Natural Resource Sciences at Washington State University.

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