Nano-sized Electron Sponge Uncovered Using X-rays

Through the help of the European Synchrotron Radiation Facility's (ESRF) X-ray beams, researchers say they have uncovered new insights into the chemical activity of certain nanoparticles.

Led by Pieter Glatzel from the ESRF and Victor Puntes from the Universitá Autònoma of Barcelona, the new study discovered that the electrons absorbed and released by cerium dioxide nanoparticles behave far differently during chemical reactions than anticipated. Rather than binding to individual atoms, the electrons distribute themselves like a cloud over the entire nanoparticle -- a distribution pattern the researchers have dubbed an "electron sponge."

Cerium is an abundant element found in the Earth's crust that is both easily mined and purified. Cerium dioxide nanoparticles are used in consumer products, such as the walls of self-cleaning ovens, and industrial processes. Many also believe they may one day comprise a key ingredient in future lithium-ion batteries capable of higher voltages and increased storage capacity, the researchers note.

However, the scientists argue, before cerium dioxide nanoparticles can be fully harnessed, they must be fully understood. Furthermore, without comprehending the chemical processes that take place on their surfaces entirely, it's impossible to know that applications are set within the bounds of safety.

Knowing that nanoparticle's behavior can change in a vacuum, the team looked at them in realistic conditions, studying them in solution and as the chemical reaction was taking place in real time.

"It is crucial to be able to study the chemical processes of the particles in an environment that is close to conditions found in biological systems," Puntes said in a statement.

They observed as the nanoparticles were created and then eliminated highly reactive molecules known as reactive oxygen species, or ROS, from the solution. ROS are found in high levels, for example, in cancer patients undergoing radiation therapy. Ceria nanoparticles have been suggested as a possible way of mitigating these levels and, as a result, lessening the negative impacts of the treatment.

Researchers have already begun the next step designed at determining whether non-localized electrons are a property of just cerium dioxide, or other nanoparticles as well.

"In parallel, chemists have to revisit their theoretical models to explain the chemical behaviour of nanoparticles and to better understand how electrons are transferred in chemical reactions taking place on their surface," Glatzel concluded.