Featured Research

from universities, journals, and other organizations

A nano-sized sponge made of electrons

Date:
November 12, 2013
Source:
European Synchrotron Radiation Facility
Summary:
During chemical reactions, ceria nanoparticles behave in a completely different way than previously thought: the electrons absorbed and released during the reaction are not bound to individual atoms but, like a cloud, distribute themselves over the whole nanoparticle. Scientists have found far-reaching consequences for optimizing the current and future use of these nanoparticles and for assessing the limits of their safe use.

This photo shows Kristina Kvashnina and Pieter Glatzel preparing an experiment at ESRF beamline ID26 where the experiments were conducted.
Credit: ESRF/A. Molyneux

A new chapter has been opened in our understanding of the chemical activity of nanoparticles says a team of international scientists. Using the X-ray beams of The European Synchrotron (ESRF) they showed that the electrons absorbed and released by cerium dioxide nanoparticles during chemical reactions behave in a completely different way than previously thought: the electrons are not bound to individual atoms but, like a cloud, distribute themselves over the whole nanoparticle. Inspired by the similarity of its shape, the scientists call this spatial distribution of particles an "electron sponge."

The results were published on 12 November in the journal ACS Nano.

The team of scientists was led by Pieter Glatzel from The European Synchrotron (ESRF), in Grenoble (France), and Victor Puntes from the Universitα Autςnoma of Barcelona, Catalan Institute of Nanotechnologies (Spain). The first author is Jean-Daniel Cafun from the ESRF.

Today, cerium dioxide nanoparticles are widely used in industrial processes and also in consumer products. They are present, for example, in the walls of self-cleaning ovens and act as a hydrocarbon catalyst during the high temperature cleaning process. They are also a hot candidate for the next generation of lithium-ion batteries which will exhibit higher voltages and a greater storage capacity compared to today's energy cells.

The element Cerium is abundant in Earth's crust and can easily be mined and purified. However, without a thorough understanding of the chemical processes that take place on the surface of cerium dioxide nanoparticles, it is impossible to optimise their current and future use. And to address a more complex issue, it is also impossible to assess the limits of their safe use.

Most chemical reactions involve the transfer of an electron from one atom to another. In the past, it was believed that the electrons involved in a chemical reaction on the surface of a nanoparticle were localised in one of the atoms at the surface. To determine the behaviour of the electrons during the reaction, the scientists used the intense X-ray beams at the ESRF to probe solutions of nanoparticles in water and ethanol. The nanoparticles had a diameter of 3 nm and consisted of several thousands of molecules of cerium dioxide.

It is known that nanoparticles can change their behaviour under vacuum when studied with an electron microscope, for example. The scientists therefore carried out their experiment under realistic conditions, studying the nanoparticles in solution and in real time as the chemical reaction was taking place. "It was only possible to conduct these experiments in a liquid rather than under vacuum because we used X-rays as probes for the electron distribution." says Jean Daniel Cafun.

X-rays reveal an unexpected property of widely used nanoparticles

In their experiment, the scientists were successful in observing the creation of the nanoparticles in solution and then how these nanoparticles eliminated highly reactive molecules (reactive oxygen species, or ROS) from the solution. This elimination process mimics the role of an important enzyme in living organisms -- catalase -- that protects cells from these aggressive molecules. Cancer patients undergoing radiation therapy have high levels of ROS in their bodies and ceria nanoparticles have been proposed as a way of reducing the levels of ROS and thus alleviating the negative impacts of the therapy on the patients. Throughout the chemical reaction, the electronic structure of the cerium atoms and thus the redistribution of the electron cloud was monitored. "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." emphasizes Victor Puntes.

Time dependent cerium high energy resolution fluorescence detection X-ray adsorption spectroscopy (HERFD-XAS) of 3nm cerium dioxide particles before any chemical reaction (red curve) and during the catalase mimetic activity (bleu curve). The enlargement of the pre-edge spectra shows that during the catalytic reaction, all Ce ions remain electron-paired in CeO2 nano particles. The redox partner is therefore not a local, spin-unpaired Ce3+ site as has been generally assumed, but the electron density that is received and released during the catalytic reaction, is delocalized over the atoms of the nanoparticle. This invokes the picture of an electron sponge as shown in the cartoon diagram. The green surface represents the electron density distribution that expands or contracts when receiving or releasing electrons.

"Scientists have been discussing the question: What happens when electrons are added to ceria nanoparticles? The work by Cafun et al. is a key study because it questions the present, widely accepted model and will lead the research in a new direction," says Frank de Groot, an expert on nanomaterials at Utrecht University who did not take part in the experiment.

The next step, which has already been initiated, will be to assess whether non-localised electrons are a property of cerium dioxide only or also of other widely used nanoparticles like titanium dioxide. "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," concludes Pieter Glatzel.


Story Source:

The above story is based on materials provided by European Synchrotron Radiation Facility. Note: Materials may be edited for content and length.


Journal Reference:

  1. Jean-Daniel Cafun, Kristina O. Kvashnina, Eudald Casals, Victor F. Puntes, Pieter Glatzel. Absence of Ce3 Sites in Chemically Active Colloidal Ceria Nanoparticles. ACS Nano, 2013; 131112081407002 DOI: 10.1021/nn403542p

Cite This Page:

European Synchrotron Radiation Facility. "A nano-sized sponge made of electrons." ScienceDaily. ScienceDaily, 12 November 2013. <www.sciencedaily.com/releases/2013/11/131112123852.htm>.
European Synchrotron Radiation Facility. (2013, November 12). A nano-sized sponge made of electrons. ScienceDaily. Retrieved July 23, 2014 from www.sciencedaily.com/releases/2013/11/131112123852.htm
European Synchrotron Radiation Facility. "A nano-sized sponge made of electrons." ScienceDaily. www.sciencedaily.com/releases/2013/11/131112123852.htm (accessed July 23, 2014).

Share This




More Matter & Energy News

Wednesday, July 23, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

Government Approves East Coast Oil Exploration

Government Approves East Coast Oil Exploration

AP (July 18, 2014) — The Obama administration approved the use of sonic cannons to discover deposits under the ocean floor by shooting sound waves 100 times louder than a jet engine through waters shared by endangered whales and turtles. (July 18) Video provided by AP
Powered by NewsLook.com
Sunken German U-Boat Clearly Visible For First Time

Sunken German U-Boat Clearly Visible For First Time

Newsy (July 18, 2014) — The wreckage of the German submarine U-166 has become clearly visible for the first time since it was discovered in 2001. Video provided by Newsy
Powered by NewsLook.com
Obama: U.S. Must Have "smartest Airports, Best Power Grid"

Obama: U.S. Must Have "smartest Airports, Best Power Grid"

Reuters - US Online Video (July 17, 2014) — President Barak Obama stopped by at a lunch counter in Delaware before making remarks about boosting the nation's infrastructure. Mana Rabiee reports. Video provided by Reuters
Powered by NewsLook.com
Crude Oil Prices Bounce Back After Falling Below $100 a Barrel

Crude Oil Prices Bounce Back After Falling Below $100 a Barrel

TheStreet (July 16, 2014) — Oil Futures are bouncing back after tumbling below $100 a barrel for the first time since May yesterday. Jeff Grossman is the president of BRG Brokerage and trades at the NYMEX. Grossman tells TheStreet the Middle East is always a concern for oil traders. Oil prices were pushed down in recent weeks on Libya increasing its production. Supply disruptions in Iraq fading also contributed to prices falling. News from China's economic front showing a growth for the second quarter also calmed fears on its slowdown. Jeff Grossman talks to TheStreet's Susannah Lee on this and more on the Energy Department's Energy Information Administration (EIA) report. Video provided by TheStreet
Powered by NewsLook.com

Search ScienceDaily

Number of stories in archives: 140,361

Find with keyword(s):
 
Enter a keyword or phrase to search ScienceDaily for related topics and research stories.

Save/Print:
Share:  

Breaking News:
from the past week

In Other News

... from NewsDaily.com

Science News

Health News

Environment News

Technology News



Save/Print:
Share:  

Free Subscriptions


Get the latest science news with ScienceDaily's free email newsletters, updated daily and weekly. Or view hourly updated newsfeeds in your RSS reader:

Get Social & Mobile


Keep up to date with the latest news from ScienceDaily via social networks and mobile apps:

Have Feedback?


Tell us what you think of ScienceDaily -- we welcome both positive and negative comments. Have any problems using the site? Questions?
Mobile iPhone Android Web
Follow Facebook Twitter Google+
Subscribe RSS Feeds Email Newsletters
Latest Headlines Health & Medicine Mind & Brain Space & Time Matter & Energy Computers & Math Plants & Animals Earth & Climate Fossils & Ruins