Sometimes smaller is better

This high-resolution transmission electron microscopy image of a metallic iron nanoparticle shows the nature of its 'protecting' shell. The chemistry of the shell appears to be crucial to the nanoparticle's ability to react with carbon tetrachloride to produce harmless byproducts.

A research team from the Pacific Northwest National Laboratory, Oregon Health and Science University, University of Minnesota and the University of Idaho is studying the ability of nanoscale iron particles to reduce carbon tetrachloride, a common groundwater contaminant. In the past, carbon tetrachloride was a common component in refrigerants, industrial degreasers and pesticides.

This chemical is now an environmental contaminant, and according to the U.S. Environmental Protection Agency, carbon etrachloride can cause liver, kidney and central nervous system damage.

One remediation method for contaminated groundwater uses microsized iron particles that react on contact with carbon tetrachloride.

However, the reaction often produces chloroform, another environmentally undesirable chemical.

The research team's studies indicate that one type of nanosized iron particle can be more effective in reducing carbon tetrachloride in water than the microsized particles while also minimizing the production of chloroform.

"The use of nanosized particles of iron for cleaning up contaminants in groundwater, soil and sediments is an exciting new technology that contributes to a general enthusiasm about nanotechnology," said Don Baer, the project's principal investigator from PNNL.

The researchers examined two iron nanoparticles, one produced by the hydrogen reduction of an iron oxide (FeH2) and the other produced by a solution synthesis (FeBH) method. The FeH2 particles had a shell made of iron oxide, and the FeBH had a shell that included boron oxide as well as iron oxide. The research study involved both the characterization of the particles and examination of their reactivity. The team determined that FeH2 produced lower quantities of chloroform in comparison to FeBH or micron-sized particles of iron.

This study suggests that nanosized iron particles with the right chemistry may be the better ingredient for new technologies to clean up carbon tetrachloride in contaminated groundwater sites around the country.