Tuesday, September 27, 2011

Chemical research could help solve radioactive waste concerns

The controversial problem of storing some of the most radioactive elements of nuclear waste could be close to being solved thanks to experts from the University of Reading.

Researchers in the Department of Chemistry have discovered a class of that can selectively extract extremely radioactive components - ‘minor actinides' - that remain after spent fuel has been reprocessed, making the eventual waste far less radiotoxic. The minor actinides can potentially be fed back into nuclear reactors, providing extra energy and, in turn, be converted to non-radioactive products.

The UK nuclear power industry produces about 10,000 megawatts of power each year. Although the vast bulk of the spent fuel from a reactor can be reprocessed and fed back into the fuel cycle, a residue, consisting of corrosion products, lanthanides and minor actinides, must be sent to storage.

For every 500kg of spent fuel, there is 15kg of waste, of which the minor actinides, such as americium, curium and neptunium, constitute less than 1kg. However, these present an extreme hazard as they are intensely radioactive and long-lived nuclides that cause serious concern when it comes to storing them for more than 100,000 years.

Professor Laurence Harwood, who led the research at Reading, said: "The minor actinides are highly radioactive and have half lives up to millions of years. If these can be removed they could be used as fuel in the new generation of nuclear reactors that will come on-stream around 2025 and converted to non-radioactive material.  Being able to separate out the minor actinides even now already makes storage simpler and reduces the security risk as well.

"Our research has produced molecules capable of removing 99.9%of the minor actinides left after reprocessing , ensuring much smaller levels of radioactive waste would accrue and remain hazardous for a much shorter period of time; a few hundred years, rather than effectively forever."

More information: The research, ‘Highly efficient separation of actinides from lanthanides by a phenanthroline-derived bis-triazine ligand', can be viewed at http://centaur.rea … 0000170.html

Provided by University of Reading

First chemical complex consisting of rare earth metals and boron atoms produces unexpected results

Boron is an intriguing member of the periodic table because it readily forms stable compounds using only six electrons—two fewer than most other main-group elements. This means that chemists can easily add boron to unsaturated hydrocarbons, and then use electron-rich atoms, such as oxygen, to change organoborons into versatile units such as alcohols and esters. Recently, researchers found that combining transition metals with boron ligands produces catalysts powerful enough to transform even fully saturated hydrocarbons into new organic functionalities with high selectivity.

Now, Zhaomin Hou and colleagues from the RIKEN Advanced Science Institute in Wako have made another breakthrough in this field: they have created the first-ever complexes between ligands and rare earth metals1. Because these novel chemical combinations display a surprising ability to incorporate molecules such as carbon monoxide into their frameworks, they have potential applications that range from synthesizing organic substrates to controlling noxious emissions.

are hot commodities because they are vital for products in high demand such as smartphones and electric cars (Fig. 1). However, full chemical studies of these elements are only in their infancy since they are difficult to handle under normal conditions. 

According to Hou, typical methods to prepare transition metal–boron complexes—halogen or metal exchange reactions, for example—seemed unsuitable for rare earth metals. Instead, the team used a vigorous lithium–boron compound to handle the reactive rare earth precursors, producing previously unseen scandium–(Sc–B) and gadolinium–boron (Gd–B) complexes in good yields, but not without difficulty. “Rare earth–boron compounds are air- and moisture-sensitive and sometimes thermally unstable,” says Hou. “They therefore require great care in isolation and handling.”

To determine whether or not the Sc–B complex could act as a nucleophile—an important electron-donating reagent in organic chemistry—the team reacted it with N,N,-diisopropylcarbodiimide, a molecule that easily accepts to change into an amidinate salt. X-ray analysis revealed that initially, the carbodiimide became incorporated between Sc and carbon ligands on the rare earth metal, but extra quantities of the reagent became incorporated between the Sc–B bond. Furthermore, adding carbon monoxide to this mixture also caused a rare earth–boron insertion, accompanied by an unexpected rearrangement into a cyclic structure. 

Because chemists rely on insertion reactions to efficiently transform ligands into a diverse range of products, these findings should enable development of brand new synthetic techniques—opportunities that Hou and his team are actively pursuing.

More information: Li, S., et al.  Rare earth metal boryl complexes: Synthesis, structure, and insertion chemistry. Angewandte Chemie International Edition 50, 6360–6363 (2011). 

Provided by RIKEN (news : web)

New material shows promise for trapping pollutants

Water softening techniques are very effective for removing minerals such as calcium and magnesium, which occur as positively-charged ions in "hard" water. But many heavy metals and other inorganic pollutants form negatively-charged ions in water, and existing water treatment processes to remove them are inefficient and expensive.

Chemists at the University of California, Santa Cruz, have now developed a new type of material that can soak up negatively-charged pollutants from water. The new material, which they call SLUG-26, could be used to treat polluted water through an ion exchange process similar to water softening. In a water softener, weakly attached to a negatively-charged resin are exchanged for the hard-water minerals, which are held more tightly by the resin. SLUG-26 provides a positively-charged substrate that can exchange a nontoxic negative ion for the negatively-charged pollutants.

"Our goal for the past 12 years has been to make materials that can trap pollutants, and we finally got what we wanted. The data show that the exchange process works," said Scott Oliver, associate professor of chemistry at UC Santa Cruz.

The chemical name for SLUG-26 is copper hydroxide ethanedisulfonate. It has a layered structure of positively-charged two-dimensional sheets with a high capacity for holding onto negative ions. Oliver and UCSC graduate student Honghan Fei described the compound in a paper that will be published in the journal and is currently available online.

The researchers are currently focusing on the use of SLUG-26 to trap the radioactive metal technetium, which is a major concern for long-term disposal of radioactive waste. Technetium is produced in nuclear reactors and has a long half-life of 212,000 years. It forms the negative ion pertechnetate in and can leach out of solid waste, making groundwater contamination a serious concern.

"It's a problem because of its environmental mobility, so they need new ways to trap it," Oliver said.

In their initial studies, the researchers used manganese, which forms the negative ion permanganate, as a non-radioactive analog for technetium and pertechnetate. The next step will be to work with technetium and see if SLUG-26 performs as effectively as it did in the initial studies.

"Whether or not it can be used in the real world is still to be seen, but so far it looks very promising," Oliver said.

Provided by University of California - Santa Cruz (news : web)

Early detection of plant disease

Each year, plant viruses and fungal attacks lead to crop losses of up to 30 percent. That is why it is important to detect plant disease early on. Yet laboratory tests are expensive and often time-consuming. Researchers are now developing a low-cost quick test for use on site.

The farmer casts a worried gaze at his potato field: where only recently a lush green field of plants was growing, much of the has now turned brown – presumably the result of a fungal disease. Usually, by the time the disease becomes visible, it is already too late. The course of the disease is then so advanced that there is little the farmer can do to counteract the damage done. To determine early on whether and how severely his are diseased, he would have to submit samples to a laboratory on a regular basis. There, researchers usually employ the ELISA method, a conventional detection method based on an antibody-antigen reaction. “These tests are expensive, though. It also takes up to two weeks before the farmer has the results of the tests. And by then, the disease has usually spread out across the entire field,” explains Dr. Florian Schröper of the Fraunhofer Institute for Molecular Biology and Applied Ecology IME in Aachen, Germany.

Researchers at the IME are now working on a new quick test that is to provide the farmer a low-cost analysis right there in the field. At the heart of the test is a magnetic reader devised by scientists at the Peter Grünberg Institute of the Forschungszentrum Jülich. The device has several excitation and detection coils arrayed in pairs. The excitation coils generate a high- and low-frequency magnetic field, while the detection coils measure the resulting mixed field. If magnetic particles penetrate the field, the measuring signal is modified. The result is shown on a display, expressed in millivolts. This permits conclusions about the concentration of magnetic particles in the field.

Researchers are making use of this mechanism to track down pathogens. “What we detect is not the virus itself but the magnetic particles that bond with the virus particles,” Schröper notes. These are first equipped with antibodies so that these can specifically target and dock onto the pathogens. This way, essentially there is a virus particle “stuck” to each magnetic particle. To ensure that these are in proportion to one another, researchers use a method that functions similarly to the ELISA principle. They introduce plant extract into a tiny filtration tube filled with a polymer matrix to which specific antibodies were bound. When the plant solution passes through the tube, the virus particles are trapped in the matrix. Following a purification step, the experts add the magnetic particles modified with antibodies. These, in turn, dock onto the antigens in the matrix. A subsequent purification step removes all of the unbound particles. The tube is then placed in an appliance in the magnet reader to measure the concentration of . The researchers have already achieved promising results in initial tests involving the grapevine virus: the measured values reached a level of sensitivity ten times that of the ELISA method. Currently, Schröper and his team are working to expand their tests to other pathogens such as the mold spore Aspergillus flavus.

The mobile mini-lab needs to be made more user-friendly, however, before it is ready for widespread use in the field. Rather than grapple with measurements in millivolts, farmers should be able to consult the display and determine directly how severe the level of crop disease is. If possible, the scientists also want to reduce the number of analytical steps, and hence the detection time involved.

Provided by Fraunhofer-Gesellschaft (news : web)