Chemical Education Today
Reports from Other Journals
Nature: “Water, Water, Everywhere, nor Any Drop to Drink”1
Since the theme for this issue of the Journal is water, and since 2003, the International Year of Freshwater (http:// www.wateryear2003.org) has just ended, it seemed fitting to reflect on the availability and quality of our planet’s freshwater. The third article in this report points to a smart, conservationminded approach to synthesizing zeolites, materials that have applications, among others, in water purification. Will We Have Enough To Drink? Although the News Feature on the global water crisis appeared in Nature early in 2003, we felt that this collection of short articles is noteworthy and particularly appropriate in this context (2003, 422, 20 March, 243; 251–256). These articles drive home rather disturbing facts about water use and misuse in the rich, developed countries and, most importantly, about the lack of access to clean water for the majority of the world’s population. Particularly moving is the article about the problems faced by Bangladesh in managing its water resources, dealing with the annual flooding and drought cycles and with the 10,000 or so freshwater wells that were established under the auspices of the UN and have turned out to be a disaster rather than a blessing, since the water in many wells is contaminated with arsenic. Despite the UN–sponsored 3rd World Water Forum in Japan in 2003
photo UNEP, 2003 International Year of Freshwater.
by Sabine Heinhorst and Gordon Cannon
Figure 1. Two streams, one with clean water and one with dirty water, coming together into the river.
(http://www.world.water-forum3.com), the outlook for sustainable management of the world’s water supply looks somewhat grim, and it is doubtful that the goal of the United Nations to lower the number of people who lack access to safe drinking water by 50% by the year 2015 will be met because of a general lack of enthusiasm by politicians, scientists, and engineers alike to tackle this less-than-flamboyant and rather costly global problem. Problem: Water Pollution
graphic by Hyunjoo Lee
Dissolved water pollutants often have very unexpected origins, as reported in a Brief Communication (2003, 425, September 18, 255–256). Researchers from the University of Ottawa, the Institute of Ocean Sciences in British Columbia, Queens University in Ontario, and the University of Alaska present strong evidence that polychlorinated biphenyls (PCBs) are taken up by salmon from ocean water and accumulate in the fish to levels of µg/g body weight. After returning to their freshwater lake spawning grounds far from the ocean, the decaying salmon release the PCBs into the lake sediment upon their death. Over a seven-year period, the authors determined profiles and amounts of PCBs in sediment cores taken from eight lakes in Alaska and compared these values to those obtained from muscle tissue of sockeye salmon. A strong correlation is evident between PCB amounts in sediments and spawning density, and the PCB profiles clearly point to spawning fish as the PCB sources. The effect the salmon-derived PCBs in these remote lakes have on salmon offspring and on mammalian and avian predators remains to be determined. New Techniques: A Silver Lining on the Horizon? Figure 2. A new zeolite synthesis route that recycles the components of the organic SDAs (green in the schematic drawing). ZSM-5 is the zeolite that was characterized in the Nature article.
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The molecular assemblies of aluminosilicates collectively known as zeolites have found applications as water purifiers through their ability to exchange ions contained in their inorganic structural framework and to absorb toxic solutes.
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Chemical Education Today
Zeolites are commonly synthesized by allowing the inorganic components to crystallize around organic molecules that direct size and shape of the micropores in the material. The high temperature required to remove these structure-directing agents (SDAs) from the zeolite pores destroys the rather expensive organic compounds and often has detrimental effects on the zeolite itself. A clever new way to circumvent these problems was reported by Lee and colleagues from the California Institute of Technology and the Chevron Texaco Energy and Research Center (2003, 425, September 25, 385–388; News and Views feature by A. Corma on 356– 357). These researchers used the reversible reaction between a cyclic ketone and ethylene glycol to synthesize a cyclic ketal as an SDA. After assembly of the zeolite, lowering the pH regenerates the original cyclic ketone and ethylene glycol, both of which are considerably smaller than the SDA. The ethylene glycol can easily be removed by liquid or gas extraction. The ionic interactions between the cyclic ketone and the zeolite are broken by ion exchange at lower pH. Re-
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cycling the expensive organic SDAs in an industrial setting should make the synthesis of zeolites for specialty applications more cost effective and lead to more widespread use of these versatile structures. To come full circle back to the beginning of this column: this new synthesis route for zeolites, once advanced beyond the proof-of-principle stage and profitable, might in the future provide affordable means of water desalination or decontamination for developing countries and help to alleviate the looming global water crisis. Note 1. The title has been quoted from the poem, The Rime of the Ancient Mariner by Samuel Taylor Coleridge (1772–1834).
Sabine Heinhorst and Gordon Cannon are in the Department of Chemistry and Biochemistry, University of Southern Mississippi, Hattiesburg, MS 39406-5043; email:
[email protected] and
[email protected].
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