A sponge for sucking up CO2

Scientists from Northwestern University are working on greener ways to squeeze tons of carbon dioxide into tiny spaces.
Written by Melissa Mahony, Contributor

The Earth’s atmosphere gained another 33 billion tons of carbon dioxide in 2010. According to a recent European Union report, the amount represents a 45 percent increase in emissions since 1990.

To bring this number down, many projects propose carbon capture and sequestration as a way we could wean ourselves off coal while we move toward more renewable energy options. Expense is a major issue for these projects as is where to safely store the CO2.

One idea is to compact as much of the greenhouse gas as we can into a tight space with lattice-like metal organic frameworks (MOFs). Similar to a sponge, these crystalline structures, invented in the nineties, are very porous with large surface areas capable of holding lots of gas. Research last year compared the surface area of 40 tons of one particular MOF (at right) to the area of California.

In the Journal of the American Chemical Society, researchers from Northwestern University recently detailed a recipe for what they call a greener MOF. Instead of using components that are typically taken from crude oil or toxic heavy metals, they make their MOFs from sugar, salt and alcohol. Sounds delicious so far, especially if you like Saltines. Metals, derived from rubidium or potassium salts, hold the sugar molecules in place and enable them to react with CO2.

Study author Jeremiah Gassensmith tells Discovery News:

In our material, the CO2 is converted into a solid, most likely by reacting with the sugar, but if you blow a stream of nitrogen over the material, the CO2 spontaneously pops off and will go wherever you blow it, and the material is reused and thus recyclable.

While the material can pack in a lot of gas for its size, it has its limits. To signal when it's time to switch MOFs out for new emissions scrubbers, the chemists added a pH indicator that changes the color of the sponge as it adsorbs CO2. Yellow means empty. Red means at least a bit of our mounting CO2 problem has been tucked away for the time being.

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Images: UCLA, Northwestern University, Flickr_SenzEnina

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