With iron hydroxide

Iron III oxide solubility

Iron oxide (rust) is a poor electrical conductor, but electrons in iron oxide can use thermal energy to hop from one iron atom to another. A Berkeley Lab experiment has now revealed exactly what happens to electrons after being transferred to an iron oxide particle. (Image courtesy of Benjamin Gilbert, Berkeley Lab)

(Phys.org)—Rust—iron oxide—is a poor conductor of electricity, which is why an electronic device with a rusted battery usually won't work. Despite this poor conductivity, an electron transferred to a particle of rust will use thermal energy to continually move or "hop" from one atom of iron to the next. Electron mobility in iron oxide can hold huge significance for a broad range of environment- and energy-related reactions, including reactions pertaining to uranium in groundwater and reactions pertaining to low-cost solar energy devices. Predicting the impact of electron-hopping on iron oxide reactions has been problematic in the past, but now, for the first time, a multi-institutional team of researchers, led by scientists at the U.S. Department of Energy (DOE)'s Lawrence Berkeley National Laboratory (Berkeley Lab) have directly observed what happens to electrons after they have been transferred to an iron oxide particle.

"We believe this work is the starting point for a new area of time-resolved geochemistry that seeks to understand chemical reaction mechanisms by making various kinds of movies that depict in real time how atoms and electrons move during reactions, " says Benjamin Gilbert, a geochemist with Berkeley Lab's Earth Sciences Division and a co-founder of the Berkeley Nanogeoscience Center who led this research. "Using ultrafast pump-probe X-ray spectroscopy, we were able to measure the rates at which electrons are transported through spontaneous iron-to-iron hops in redox-active iron oxides. Our results showed that the rates depend on the structure of the iron oxide and confirmed that certain aspects of the current model of electron hopping in iron oxides are correct."

Gilbert is the corresponding author of a paper in the journal Science that describes this work. The paper is titled "Electron small polarons and their mobility in iron (oxyhydr)oxide nanoparticles." Co-authoring the paper were Jordan Katz, Xiaoyi Zhang, Klaus Attenkofer, Karena Chapman, Cathrine Frandsen, Piotr Zarzycki, Kevin Rosso, Roger Falcone and Glenn Waychunas.

At the macroscale, rocks and mineral don't appear to be very reactive – consider the millions of years it takes for mountains to react with water. At the nanoscale, however, many common minerals are able to undergo redox reactions – exchange one or more electrons – with other molecules in their environment, impacting soil and water, seawater as well as fresh. Among the most critical of these redox reactions is the formation or transformation of iron oxide and oxyhydroxide minerals by charge-transfer processes that cycle iron between its two common oxidation states iron(III) and iron(II).

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