by: Eui Whan Moon, Baker ’11
Looking back on the years I have lived in the central Asian country of Kyrgyzstan, one of my lasting memories takes place in the small, crowded kitchen of our home. Upon our first arrival to the country, my parents and I were strictly warned by other Korean expatriates that it was unsafe to consume tap water that had not been processed. Consequently, my family promptly learned and adopted the purification process. The task is simple, consisting of boiling, cooling, decanting, and filtration (aided by our faithful Brita® jug). Since drinking water is an every day necessity, this ritual has run its course in our kitchen on an endless loop for fourteen years to this very day. If I was bored, I could always count on finding a ten-gallon pot of cooling water on the kitchen stove, waiting to be filtered. All this to say, water is a daily essential, and clean water even more so. Yet many regions of the world do not have this luxury; in effect, countless lives are claimed each year by the harmful pollutants present in the drinking water. However, a recently discovered property of iron oxides may hold a promising application to alleviating the problem of water contamination around the globe.
Here in the United States, every municipal water system is accountable to Environmental Protection Agency (EPA) regulations to provide safe drinking water to each home.1 Nonetheless, there are many developing countries and cities that cannot afford such a system, and thus to pour a cup of tap water is perilous for their inhabitants. In a number of Asian countries groundwater — a key resource for rural communities — is contaminated with dangerous levels of harmful microorganisms, inorganic chemicals, and organic chemicals. A giant among these various contaminants is the inorganic chemical, arsenic.2 Arsenic – a colorless, odorless, and tasteless element – causes various health defects upon ingestions, including skin damage, failure of the circulatory system, and cancer.1 On March 2005, The World Bank and Water and Sanitation Program presented a report on their comprehensive study of groundwater in Asian countries. The study revealed that parts of Bangladesh, China, India, Vietnam, Nepal, and Myanmar were just a few of the numerous hotspots for arsenic contamination. Overall, an estimated sixty-five million people were subject to health risks due to critical levels of arsenic in water.2 “Crisis” understates the potentially deadly arsenic situation at hand in Asia, as well as many other parts of the world not mentioned. Furthermore, Asia is only one of many other regions facing this problem. The influence of arsenic contamination is so lethal and widespread that the word “crisis” understates the situation at hand.
Meanwhile in the western hemisphere, a handful of scientists at Rice University’s Center for Biological and Environmental Nanotechnology (CBEN) are studying a promising remedy for arsenic contamination. The key to this solution was the discovery of strange magnetic properties among nano-scale magnetite particles. Magnetite (Fe3O4) is an iron oxide, much like rust, so the term “nanorust” was coined for magnetite nano-particles. Whereas rust (FeO) only contains iron in +2 oxidation states, Fe3O4 has iron in both +2 and +3 states. Nanorust crystals are so tiny that they are measured in the scale of nanometers (10-9 meters). At this size, magnetite was found to behave differently under the influence of a magnetic field in comparison to its counterpart with more conventional dimensions. For instance, based on observations made on bulk material it would take an extraordinarily large magnetic field to extract magnetite nanoparticles suspended in a solution. Yet Dr. Vicki Colvin, the director of CBEN, and her colleagues discovered to their surprise that removing nanorust particles from a solution required only a small electric field. Dr. Colvin told Chemical and Engineering News, “We were surprised to find that we didn’t need large elecromagnets to move our nanoparticles, and in some cases, handheld magnets could do the trick.”3 Another property of nanorust is that it has a very high surface area per mass because the particles are so small. The principle here is simple. Picture a very large copper sphere and a very small copper sphere. Most of the atoms in the large sphere are inside the sphere, not on its surface; the opposite is true for the small sphere. Therefore, comparing a one kilogram copper sphere to a kilogram of nano-sized spheres will show that the latter mass has much more surface area. In the case of nanorust particles, a kilogram has enough surface area to cover an entire football field.4
So how exactly do the properties of nano-scale magnetite help solve the arsenic problem? Arsenic has a high affinity toward iron oxides. Regardless, the use of conventional-sized iron oxides for purifying water has largely proven to be impractical, inefficient, and tedious.4 On the other hand, using nanocrystals of iron oxide for the job is an entirely different matter. Due to its exceptional surface area (which translates to more binding spots for arsenic) a given mass of magnetite particles twelve nanometers in diameter can capture one hundred times more arsenic than the equal mass of the larger iron oxide counterparts used in filters today.5 Once all the arsenic has been collected by the magnetite, these nanoparticles are easily removed from the water using a simple hand magnet. In describing this process to Science Daily, Dr. Colvin claimed, “Arsenic contamination in drinking water is a global problem and while there are ways to remove arsenic, they require extensive hardware and high-pressure pumps that run on electricity . . . . Our approach is simple and requires no electricity.”6 The only problem is the cost; nanorust particles assembled from pure laboratory chemicals can be very expensive. Key ingredients for water soluble nanorust are rust (FeO) and a fatty acid mixture (oleic acid). Heating rust yields magnetite. A double layer coating of oleic acid is then applied to each magnetite nanoparticle; by doing so, the nanoparticles will not stick to one another but instead be dispersed throughout water. Cafer Yuvez, a graduate student working under Dr. Colvin, is developing a method to create nanorust particles using inexpensive household items such as rust, olive oil (source of fatty acid), drain opener, and vinegar. Once perfected, this method will drastically reduce the production cost of nanorust from $2,624 to $21.5 per kilogram.7 Perhaps one day millions of people threatened by arsenic will be saved by nanorust cooked up on their kitchen stoves.
References
1. Drinking water Contaminants. http://www.epa.gov/safewater/contaminants/index.html (accessed 03/20/08), part of United States Environmental Protection Agency.
2. Arsenic Contamination in Asia. http://siteresources.worldbank.org/INTSAREGTOPWATRES/Resources/ARSENIC_BRIEF.pdf (accessed 03/20/08), part of a World Bank and Water and Sanitation program Report.
3. Cleaning Water With ‘Nanorust’. http://pubs.acs.org/cen/news/84/i46/8446notw4.html (accessed 03/20/08), part of Chemical and Engineering News.
4. Merali, Zeeya. Cooking up ‘Nanorust’ Could Purify Water. http://technology.newscientist.com/article.ns?id=dn10496&print=true (accessed 03/20/08), part of New Scientist Tech.
5. Feder, Barnaby J. Rustlike Crystals Found to Cleanse Water of Arsenic Cheaply. http://www.nytimes.com/2006/11/10/science/10rust.html (accessed 03/20/08), part of The New York Times.