Chemical Education Today
Reports from Other Journals
Research Advances by Angela G. King
New CO2 “Sponge” Scientists and engineers in Georgia and Pennsylvania are reporting development of a new, low-cost material for capturing carbon dioxide from the smokestacks of coal-fired electric power plants and other industrial sources before the notorious greenhouse gas enters the atmosphere. In the new study, Christopher W. Jones and colleagues point out that existing carbon capture technology is unsuitable for wide use because it is energy intensive and/or expensive. Aqueous amines, for instance, use temperature swings for CO2 desorption despite the high heat capacity of water. Current solid adsorbents show promise, but many suffer from low adsorption capacities and lack stability after extended use. Stronger, longer-lasting materials are needed, scientists say. The scientists describe development of a new solid adsorbent coined a “hyperbranched aminosilica” (HAS) that avoids those problems and can reversibly bind CO2 from simulated flue gas. HAS was prepared in one step by reacting aziridine and a silica surface. From previous work, the research team knew that surface silanols initiate aziridine polymerization off the surface with catalytic amounts of acetic acid present. They chose a meso porous silica material (SBA-15) instead of silica wafers because of the mesopore’s high surface area. To assay the ability of the new material (SBA-HA) to capture CO2, it was dispersed in sand and tested in a fixed bed flow system. The absorption of CO2 on the new material was determined by using mass spectrometry to monitor effluent gas. The captured CO2 was desorbed by switching the gas flow to pure argon and heating the material to 130 °C for at least three hours. Over 11 separate tests, SBA-HA reversibly captured carbon dioxide with an average capacity of 1.98 mmol CO2/g adsorbant. When compared to traditional solid adsorbents under simulated emissions from industrial smokestacks, SBA-HA captured up to seven times more carbon dioxide than conventional solid materials, including some of the best carbon dioxide adsorbents currently available. The material also shows greater stability under different temperature extremes, allowing it to be recycled numerous times. Combined with its ease of synthesis and low cost, the CO2 capturing ability of SBA-HA offers great promise for future applications.
3. Additional information on Jones’s research, which focuses on different aspects of catalysis and absorption, can be found online at http://www.chbe.gatech.edu/jones/ (accessed Jun 2008). 4. More information on the CO2 Capture Project, an international effort by leading energy companies to reduce CO2 emissions from combustion, may be found at http://www.co2captureproject.org/ Phase2Index.htm (accessed Jun 2008). 5. Newspapers around the U.S. have featured articles on CO2 capture. For instance, http://www2.journalnow.com/content/2008/may/19/ researchers-press-efforts-to-find-way-to-reduce-th/ (accessed Jun 2008).
Big Molecules with a Big Future Scientists report discovery of a new method that will enable manufacturers to produce industrial-size batches of dendrimers. Dendrimers are polymers but not of the traditional long chain variety (Figure 1). They have a core with tree-like branches and offer a range of potentially valuable commercial and industrial applications. Dendrimers can be produced in custom-designed shapes, sizes, structures, and masses suitable for specific uses. Those potential applications range from drug delivery and gene transfer to new materials, coatings, sensors, and herbicides. But because they require multiple steps to make, dendrimers are difficult to produce on an industrial scale. In their new study, Abdellatif Chouai and Eric E. Simanek describe a practical large-scale synthesis of dendrimers that sidesteps this barrier (Scheme 1). Their method yields a so-called “uncommitted intermediate, a dendrimer scaffolding that can be built upon in countless ways”. This intermediate, 1, represented by G2 (generation two) in Scheme 1, “can be elaborated into a wealth of diagnostic and therapeutic dendrimers” the researchers add (Figure 2).
More Information 1. Hicks, Jason C.; Drese, Jeffrey H.; Fauth, Daniel J.; Gray, McMahan L.; Qi, Genggeng; Jones, Christopher W. Designing Adsorbents for CO2 Capture from Flue Gas—Hyperbranched Aminosilicas Capable of Capturing CO2 Reversibly. J. Am. Chem. Soc. 2008, 130, 2902–2903. 2. This Journal has published both an integrated lecture-lab case study and a demonstration on the greenhouse effect, both of which relate to this research. See J. Chem. Educ. 2000, 77, 1602 and 1993, 70, 73, respectively. 1166
Figure 1. Dendrimers could serve a variety of functions, including improving drug delivery to materials. Scientists now report a method to manufacture them on an industrial scale for the first time. Reprinted with permission from J. Org. Chem. 2008, 73, 2357–2366. Copyright 2008 American Chemical Society.
Journal of Chemical Education • Vol. 85 No. 9 September 2008 • www.JCE.DivCHED.org • © Division of Chemical Education
Chemical Education Today
Scheme 1. G2 represents the first synthetic target (1), an uncommitted intermediate in the preparation of diagnostic or therapeutic candidates. Reprinted with permission from J. Org. Chem. 2008, 73, 2357–2366. Copyright 2008 American Chemical Society.
NHBoc N
N N
N
NHBoc
N NHBoc
NH BocHN
N
N N
BocHN
N
N N
N
N N
N N
N
NHBoc
N N
N
HN N
N N
N
N
H N
H N
N
N N
NHBoc NHBoc
N
N
N N
N
N N
N
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N
N N
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N N
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BocHN N BocHN
N N
NH
HN
N
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NHBoc N NHBoc
1 Figure 2. Target 1 features 12 protected amine groups. Reprinted with permission from J. Org. Chem. 2008, 73, 2357–2366. Copyright 2008 American Chemical Society.
Chouai and Simanek based their approach to dendrimer synthesis on 2,4,6-trichloro-1,3,5-triazine (cyuranic acid), a readily available and inexpensive core reagent that can undergo sequential nucleophilic substitution of chlorine atoms with primary or secondary amines. The stepwise reactions can be controlled by temperature (0 °C, room temperature, or >60 °C) and can all occur in one pot. On the scales used in their lab, the researchers report that 1 was prepared at a cost of
