Removing toxic pollutants from water typically requires a number of steps. The aberrant molecules must first be identified, then destroyed or extracted. Finally, the water is tested to ensure its purity. According to a report in the current issue of the Journal of Physical Chemistry B, a single smart material could conceivably execute all three of these stages.
Previous research had shown the compound titanium dioxide to have pollution-fighting potential. Prashant Kamat and colleagues at the University of Notre Dame thus set out to investigate whether a similar compound, zinc oxide (ZnO), could degrade organic contaminants in water. They tested the material against a class of organic aromatic pollutants known as chlorinated phenols. (Widely used as preservatives and pesticides, and produced by industries such as pulp mills, paint and plastic manufacturers, chlorinated phenols are a common water contaminant.) Typically, ZnO emits visible radiation. When the material was exposed to water contaminated with a type of chlorinated phenol, however, the amount of light emitted dropped drastically. The researchers further found that this response was measurable for pollution concentrations as low as one part per million and occurred in under a minute.
Moreover, once the ZnO detects the offending organic molecules, it can also help eliminate them. When exposed to UV light, ZnO aids in the breakdown of the contaminants without being destroyed itself. After the pollutants have been converted into harmless byproducts, the ZnO film begins to glow more brightly, signaling that its job is done. Though commercial applications are not yet available, the researchers suggest that "ZnO film-based nanosensors should be useful in applications such as checking the quality of drinking water, or assessing the contamination in underground water."