Molecular Cage Filters Rare and Dangerous Gases
Mark Atwater posted on July 20, 2014 | | 3844 views
Filtering gases out of the air has been commonplace for quite some time, but not all gases are easily sorted. Noble gases, for instance, don’t readily react with other elements, so they pose somewhat of challenge. The lower the concentration, the more difficult and inefficient the process becomes. Some new research, however, may improve efficiency and even help save lives.

Researchers at the University of Liverpool, in conjunction with the Pacific Northwest National Laboratory, have developed a new material with atomic selectivity. The technique uses an organic cage molecule, called CC3, to trap gas atoms of just the right size. Atoms which are not the correct dimensions are not collected, thereby operating with exceptional selectivity.

According to the University of Liverpool, “By a process of adsorption – where molecules or atoms stick onto the surface – the right gas molecules are held in place, while others such as water or nitrogen are released.” This concept of collecting matter through molecular cages is not new and not limited to atoms (see concept for nitrobenzene in image), but the development for noble gases does introduce some promising applications. CC3 has been found efficient at collecting xenon, krypton and radon.

Researchers used computer simulation to study the molecular cage structure of CC3 and found that it undergoes a natural expansion and contraction which oscillates around the size of xenon, krypton and radon. As the cage expands, the gas atom enters, and as it contracts, it becomes effectively trapped, having a higher likelihood of entering than exiting. (More on this mechanism here)

While xenon and krypton have a variety of research and industrial uses (like dark matter detection, for xenon), these elements are typically expensive due to their rarity and noble nature. Radon, on the other hand, is a common killer, accounting for 21,000 deaths per year according to a 2010 Surveillance, Epidemiology, and End Results (SEER) analysis.

The Environmental Protection Agency (EPA) action limit on radon is 4 pCi/L, a level at which you have the same likelihood of dying from radon as you would in a car crash. It’s higher if you smoke. Although there are radon mitigation systems readily available which use a pressure differential to keep radon out, a method of filtration and/or precise detection could greatly enhance general well-being.

The CC3 material does show promise for being an effective means for separating these gases, especially as it operates at or near room temperature whereas current separation methods rely on expensive, cryogenic operations. That said, don’t be looking for a CC3 radon filter on the supermarket shelf just yet. Hopefully, though, this sort of work will result in some trickle down improvements to daily life.

If you can get access and are interested, the scientific article, published in Nature Materials, is here.


Image courtesy of Wikipedia

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