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To understand why this innovation is being hailed as a "step-change" in carbon capture technology, it's helpful to first know more about its structure.3 The material is a metal-organic framework—a new class of crystalline structures synthesized with clusters of metal ions and organic molecules. Their microporous design creates extremely high internal surface areas, as in the "highest experimental... surface areas of any porous materials reported to date."4 To give an idea of this record-breaking capacity, a single gram of the material has the same surface area as a football field.5
While it's long been clear that this feature allows metal-organic frameworks to adsorb massive volumes of gas, it's only now becoming more apparent how to apply this trait to reduce greenhouse gas emissions. Specifically, for any material to facilitate carbon capture and sequestration, it has to not only trap carbon, but also be able to then release it into a storage reservoir.6
To achieve these two important requirements, researchers have incorporated light-sensitive azobenzene molecules into a metal-organic framework, which have both an affinity for carbon and the ability to release adsorbed CO2 when exposed to specific solar wavelengths. Just like wringing water from a sponge, with this dynamic photo-switching, captured carbon can be caught and dropped from a reusable stable structure.
With its impressive, low-energy approach to storage, the resourceful design of the "carbon sponge" addresses several criticisms of clean coal, namely, that the technology is years away from being implemented and that it's financially prohibitive.7 However, while some hope that this advance will prolong coal's role by allaying its environmental impact, I have to wonder whether research in technologies for cleaner fossil fuels, albeit clever ones, divert attention and funds from alternative energies like microalgae biofuel.
China, for instance, burns about as much coal as the rest of the world combined,8 and I can see how this invention theoretically could assist with its staggering air pollution. In practice, though, I am cautious to trust that a device could be developed in time to offset the tons of emissions already being generated. While I believe that China and all countries need energy to thrive, even with this advance for coal, I think there still may be cleaner and safer sources. If a carbon reservoir of the magnitude China demands were to leak, countless people could be harmed, as occurred in 1986 near Lake Nyos, Cameroon, when thousands of people died due to a release of CO2 from a volcanic reservoir.9
Moreover, even if the new material eventually could purify all of coal's greenhouse gas emissions, it fails to address its other ecological effects, including those that come from extraction itself. Increasingly, underground coal excavation is being replaced with mountaintop removal mining, a process that's as bleak as it sounds: as summits are exploded to unearth highland coal seams, defaced peaks and filled valleys are left behind, along with toxic byproducts linked to serious health problems.10,11
Similar to how the eighteenth-century invention of the steam engine spurred intensive coal mining, this novel material may encourage coal's continuance and at a high risk. Even if an optimized carbon sponge were perfected, it still could leave a mess.
Image of coal by Flickr's Jeffrey Beall.
1. Freese, Barbara. Coal: A Human History. Vintage. 2006.
2. Lyndon R, Konstas K, Ladewig BP, Southon PD, Kepert PC, & Hill MR (2013). Dynamic photo-switching in metal-organic frameworks as a route to low-energy carbon dioxide capture and release. Angewandte Chemie (International ed. in English) PMID: 23401101
3. Monash University. "Carbon Sponge Could Soak Up Coal Emissions." Press Release. February 12, 2013.
4. Farha OK, Eryazici I, Jeong NC, Hauser BG, Wilmer CE, Sarjeant AA, Snurr RQ, Nguyen ST, Yazaydın AÖ, & Hupp JT (2012). Metal-organic framework materials with ultrahigh surface areas: Is the sky the limit? Journal of the American Chemical Society, 134, 15016-15021 PMID:22906112
5. Monash University, Ibid.
6. Chu, S. (2009). Carbon capture and sequestration Science, 325, 1599-1599 DOI: 10.1126/science.1181637
7. Greenpeace. "False Hope: Why Carbon Capture And Storage Won't Save The Climate." Executive Summary. May 2008.
8. Walsh, Bryan. "The Scariest Environmental Fact in the World." Time. January 29, 2013.
9. Baxter PJ, Kapila M, & Mfonfu D (1989). Lake Nyos disaster, Cameroon, 1986: the medical effects of large scale emission of carbon dioxide? BMJ (Clinical research ed.), 298, 1437-1441 PMID: 2502283
10. Ahern MM, Hendryx M, Conley J, Fedorko E, Ducatman A, & Zullig KJ (2011). The association between mountaintop mining and birth defects among live births in central Appalachia, 1996-2003. Environmental research, 111, 838-46 PMID: 21689813
11. Hendryx M, Wolfe L, Luo J, & Webb B (2012). Self-reported cancer rates in two rural areas of West Virginia with and without mountaintop coal mining. Journal of community health, 37, 320-327 PMID: 21786205
