TECHNOLOGY: Nanorust

Water purification has become a major issue in third world countries, where thousands of people die each year from arsenic contamination in their drinking water wells. A lab at Rice University recently published an article in Science magazine describing small crystals containing Fe3O4 rust particles dubbed "nanorust", which may prove to be an answer to low-cost and effective water purification in these countries. These nanorust crystals serve as another example of how the unique properties of nanoscale materials can be applied in today's industries.

A general principle of magnetics states that as particles get smaller, the amount of magnetic force required to move the particles increases. This relationship is due to the fact that magnetic power is proportional to the volume of the material acted upon, so when particles get too small their magnetic power potential falls below the threshold required to overcome initial inertia. A lab at Rice led by Dr. Vicki Colvin sought to test this principle on the nanoscale and found that, after reaching a critical threshold of approximately 50 nm, it becomes easier to manipulate the materials. This, they propose, is due to the fact that at this miniscule size, the particles exert forces on each other in a cooperative manner that allows for magnetic separations with even weak handheld magnets.

After proving this concept of nanoscale separation, Dr. Colvin's lab tested the potential of this method to remove arsenic from drinking water. Taking advantage of the tendency of rust to bind arsenic, the lab found that adding nanorust to water and applying a magnetic field effectively removed the arsenic and purified the water enough to meet EPA standards.

The benefits of this method of magnetic separation over traditional separation methods such as centrifugation and filtration are a few fold. The process is not only more selective and efficient than its counterparts, but it may also turn out to be a much cheaper method. While Dr. Covlin admits that the process is too expensive to currently use in water filtration, they claim to be working on methods that will eventually produce nanorust at a very low cost and scalable level.

(FIGURE from TechnologyReview.com)