Very Heavy Elements Deliver More Electrons

The Science

Actinides, a series of 15 radioactive elements, are vital to medicine, energy, and national defense. Scientists examined two exceedingly rare actinides, berkelium and californium. These elements are at the extreme end of what is possible to synthesize in more-than-atom amounts for chemical study. These elements are only available in tiniest amounts. The scientists showed that the elements can lose electrons to bond like lighter actinides. Specifically, they found the +5 oxidation state is much more stable than expected, and similar to the stability found for lighter actinides.

The Impact

Due to the difficulty in studying these radioactive and rare elements, most of which have only been studied since the Manhattan Project, there is much to learn. Fundamental knowledge about the most basic, yet unknown, chemistry of the actinides, such as knowing better how two more actinides, berkelium and californium, form bonds at high oxidation states, could benefit environmental cleanup at nuclear production sites. Such knowledge could also aid in developing new nuclear fuels and their reprocessing. Further, this work resolves a longstanding uncertainty about actinides.

Summary

When forming bonds with oxygen or participating in reactions involving oxygen atom transfer, the early actinide elements, protactinium through curium, can attain the +5 oxidation state when bonded to two oxygen atoms. Scientists wanted to know if this oxidation state is important in bonding for berkelium and californium (the next two actinides in the series after plutonium, americium, and curium). The team synthesized positively charged berkelium and californium molecules that contain oxygen atoms within a mass spectrometer. They created these molecules, BkO2+ and CfO2+, by transferring to the actinide monoxide cations a second oxygen atom from the common gas nitrogen dioxide. The team’s high-level electronic structure calculations showed that the produced molecules are linear, a significant characteristic of positively charged pentavalent dioxide ions of the actinides. The dissociation energies to break the actinide-oxygen bonds, which are at least 73 kcal/mol, are surprisingly high. These first pentavalent berkelium and californium species reveal that the +5 oxidation state is possible farther into the actinide series than previously recognized, which is key to understanding the essential nature and chemistry of these elements.

Source : Department of Energy (DOE), Office of Science

Electronic Processes Observed During Catalysis with Novel X-Ray Spectroscopy Method

Electronic processes
Also in photosynthesis manganese compounds play a role as catalysts. Picture: HZB

An international team has achieved a breakthrough at BESSY II. For the first time, they were able to study electronic processes on a transition metal in detail and draw reliable conclusions from the measured data on their catalytic effect. Their results are useful for the systematic development of catalytic systems with transition metals in their centers for future applications. The work is now published in Chemical Science, the Open Access Journal of the Royal Society of Chemistry.

Many important processes in nature require catalysts: atoms or molecules that allow the desired reaction, but which are themselves unaltered. An example is the photosynthesis in plants, which is only possible with the help of a protein complex, in the center of which four manganese atoms sit. Often, in such processes so-called redox reactions play a crucial role, in which the reactants exchange electrons and thereby reduced (electron uptake) or oxidized (electron donation) are. Catalytic redox processes in nature or in technology often succeed only thanks to suitable catalysts in which transition metals play an important role.

Soft X-ray from BESSY II

Such transition metals and in particular their redox or oxidation state can be examined particularly well with soft X-ray light. In so-called L-edge absorption spectroscopy, electrons from the 2p shell of the transition metal are excited to occupy free d orbitals at short notice. The X-ray absorption spectrum can be used to determine an energy difference which is known to reflect the oxidation state of the molecule or of the catalyst. Where exactly in the catalyst during a redox reaction, however, the electrons are absorbed or released, how exactly the charge density in the catalyst changes with a change in its oxidation state, was previously largely unknown. This was mainly because that reliable methods for theoretical descriptions of the charge densities in catalyst molecules were missing and that reliable experimental data are difficult to obtain. If the transition metals are present in larger, organic molecular complexes, as is typical of functioning redox catalysts, the investigation becomes extremely difficult, since the X-ray radiation immediately leads to damage in the sample.

Sample tested in solution in different oxidation states

For the first time ever, an international team from HZB, Uppsala University (Sweden), the Lawrence Berkeley National Laboratory at Berkeley (USA), Manchester University (UK) and the SLAC National Accelerator Laboratory at Stanford (USA) are taking measurements on BESSY II succeeded in investigating manganese atoms in different compounds and oxidation states in operando – that is, during different oxidation states. The researchers led by Philippe Wernet brought the samples in different solvents, examined the liquid jet in X-rays and compared the measured data with novel calculations from the group of Marcus Lundberg from Uppsala University. “We were able to determine how, and above all, why the X-ray absorption spectra shift with the oxidation states,” as the theorist Marcus Lundberg. The two doctoral students Markus Kubin (HZB) with his experimetnellen and Meiyuan Guo (Uppsala University) with his theoretical expertise reflect the interdisciplinary approach of the study and contributed in equal parts as first authors of the study.

Breakthrough through combination of theory and experiment

“We have combined a novel experimental set-up with quantum-chemical model calculations and thereby, we believe, achieved a breakthrough in the understanding of organometallic catalysts” says Wernet: “For the first time, we were able to compute oxidation or reduction calculations not locally on the metal but on These findings are an important cornerstone for future work in photosynthesis: “They will enable a novel understanding of the redox processes in the manganese catalyst of the photosystem II protein complex,” says Junko Yano, who intensively researching photosynthesis.

Source : Helmholtz-Zentrum Berlin für Materialien und Energie

A Spicy Finding

Extracts of the plant turmeric — the spice that gives Indian curries a yellow color — have been used as an anti-inflammatory treatment in traditional Asian medicine for centuries. Clinical trials of curcumin (the active chemical compound in turmeric), however, have produced mixed results. A molecular understanding of curcumin’s biological effects is needed.

Claus Schneider, PhD, and colleagues have now discovered that curcumin is a “pro-drug” that is converted into reactive metabolites with anti-inflammatory activities. The metabolites of curcumin, produced by oxidation reactions, covalently bind to and inhibit proteins in the inflammatory NF-kappa-B signaling pathway.

The researchers found that curcumin undergoes oxidation reactions readily in vitro. They suggest that insufficient bioactivation in vivo may explain the mixed results in human studies of curcumin activity.

The findings, reported in the Journal of Biological Chemistry, suggest that metabolic bioactivation should be considered in clinical trials of curcumin and other dietary polyphenols of medicinal interest, such as resveratrol (red wine), quercetin (onions) and epigallocatechin gallate (green tea).

This research was supported in part by the National Institutes of Health (grant AT006896) and in part by pilot awards from the Vanderbilt Institute of Chemical Biology and the National Cancer Institute SPORE in GI Cancer (grant CA095103).

Source : Vanderbilt University

Scientists Decipher Key Principle Behind Reaction of Metalloenzymes

What enables electrons to be transferred swiftly, for example during photosynthesis? An interdisciplinary team of researchers has worked out the details of how important bioinorganic electron transfer systems operate. Using a combination of very different, time-resolved measurement methods at DESY‘s X-ray source PETRA III and other facilities, the scientists were able to show that so-called pre-distorted states can speed up photochemical reactions or make them possible in the first place. The group headed by Sonja Herres-Pawlis from RWTH Aachen University, Michael Rübhausen from the University of Hamburg, and Wolfgang Zinth from Munich’s Ludwig Maximilian University, is presenting its findings in the journal Nature Chemistry.

The scientists had studied the pre-distorted, “entatic” state using a model system. An entatic state is the term used by chemists to refer to the configuration of a molecule in which the normal arrangement of the atoms is modified by external binding partners such that the energy threshold for the desired reaction is lowered, resulting in a higher speed of reaction. One example of this is the metalloprotein plastocyanin, which has a copper atom at its centre and is responsible for important steps in the transfer of electrons during photosynthesis. Depending on its oxidation state, the copper atom either prefers a planar configuration, in which all the surrounding atoms are arranged in the same plane (planar geometry), or a tetrahedral arrangement of the neighbouring ligands. However the binding partner in the protein forces the copper atom to adopt a sort of intermediate arrangement. This highly distorted tetrahedron allows a very rapid shift between the two oxidation states of the copper atom.

“Pre-distorted states like this play an important role in many biochemical processes,” explains Rübhausen, who works at the Centre for Free-Electron Laser Science (CFEL) in Hamburg, a cooperation between DESY, the University of Hamburg and the Max Planck Society. “The principle of the entatic state helps the electron transfer reactions that occur everywhere in nature and also in human beings, for example when we breathe or a plant photosynthesises,” adds Herres-Pawlis.

Biologically relevant, pre-distorted states always involve a metal atom. The scientists examined a model system consisting of a copper complex with specially tailored molecules bound to it, so-called ligands. Using a wide range of observation methods as well as theoretical calculations, the scientists showed that the ligands used did indeed put the copper complex into a pre-distorted (entatic) state and were then able to observe the details of the reaction that occurred when light was absorbed.

The combination of time-dependent UV, infra-red, X-ray and visual fluorescence spectroscopy produces a detailed picture of the dynamics of the structural changes on a timescale of pico- to nanoseconds (trillionths to billionths of a second). “We are now able for the first time to understand how pre-distorted states favour charge transfer,” explains Rübhausen. “Also, our studies demonstrate that pre-distorted states are important for photochemical reactions, in other words for certain biochemical processes which are triggered by light,” explains Herres-Pawlis.

The study shows in detail how the process proceeds: from the initial state (copper in an oxidation state of +1) an electron is transferred from the copper to one of the ligands, by optical excitation. Within femtoseconds (trillionths of a second) the excited state created decays into another, still excited state, known as the S1 state. In this configuration, the geometry is slightly relaxed.

Shortly afterwards, the electron undergoes a change in spin. The spin of an electron is comparable to the direction in which a top rotates. Although one of the electrons has so far remained on the ligand, this electron and its corresponding partner on the copper were spin-coupled. The spin of the electron on the ligand now reverses, and this very rapid transition to the so-called triplet state, within just about two picoseconds, removes the spin coupling. This T1 state exists for 120 picoseconds and drops back into the original state again after once again reversing its spin. All the time constants are distinctly shorter compared with other copper complexes. “A complete understanding of all the processes taking place has only become possible through the unique combination of different methods of study,” emphasises Zinth.

The detailed analysis of the reaction principle not only improves our understanding of natural processes. It can also help to customize new bioinorganic complexes that imitate nature but whose range of reactions extend beyond those of natural molecules. These complexes could also accelerate or make possible chemical reactions associated with electron transfers in other areas as well.

Scientists from the University of Hamburg, RWTH Aachen University, the Ludwig Maximilian University in Munich, DESY, the University of Paderborn, the European research facility ELI Beamlines, the Institute of Physics of the Czech Academy of Sciences, the University of Uppsala, Chalmers University of Technology in Gothenburg, European XFEL and the Danish Technical University were all involved in the research.

The study received grants from Deutsche Forschungsgemeinschaft as part of the DFG Research Unit FOR 1405(Dynamics of Electron Transfer Processes within Transition Metal Sites in Biological and Bioinorganic Systems), the Collaborative Research Centre SFB 749 (Dynamics and Intermediates of Molecular Transformations) and theCIPSM Cluster of Excellence.

Source : RWTH Aachen University

Maintaining Canola Oil Quality

Canola and other edible oils are easily affected by light irradiation or heat treatment. Since such processes deteriorate the oil quality such as flavor or taste, understanding this process, called oxidation, is imperative to identify effective measures to control the oil quality such as the best way to package or store oil.

A team of researchers from Tohoku University and their colleagues have provided the most detailed picture to date of canola oil’s oxidation process by high performance liquid chromatography (HPLC) combined with tandem mass spectrometry (MS/MS). HPLC pumps liquid under high pressure through a granular adsorbent material to separate the different components contained in the liquid. MS/MS bombards the compound molecules separated by HPLC with neutral molecules (e.g. nitrogen) to break it apart into smaller components, and then measures the mass-to-charge ratio of the pieces.

canola oil
Detailed quantitative analysis of oxidized canola oil was performed using high performance liquid chromatography (HPLC) combined with tandem mass spectrometry (MS/MS), providing valuable insight for preserving the quality of edible oil.

Triacylglycerol (TG), a major component of edible oil, is known to form different oxidation compounds, or isomers, depending on how TG was oxidized. The researchers developed a new technique to analyze isomers using HPLC-MS/MS. Using the method, they identified the specific oxidation compounds in canola oil resulting from heat (25-180°C) and light (office lighting-direct sunlight).

Moreover, they found that marketed canola oil tends to be oxidized by light around room temperature. This suggests that canola oil should be packaged in dark containers to extend shelf life by reducing light exposure. Another method to reduce oxidation could be to add antioxidants such as carotenoids, that trap oxygen before it interacts with the oil.

The new method enables a more detailed quantitative analysis of oxidized edible oil compared to other existing methods. The researchers suggest in their paper recently published in the journal npj Science of Food that this approach would be valuable in understanding oil and food oxidation processes, and the development of preventive methods against food deterioration.

Source : Tohoku University

Which Came First: Complex Life or High Atmospheric Oxygen?

We and all other animals wouldn’t be here today if our planet didn’t have a lot of oxygen in its atmosphere and oceans. But how crucial were high oxygen levels to the transition from simple, single-celled life forms to the complexity we see today?

A study by UC Berkeley geochemists presents new evidence that high levels of oxygen were not critical to the origin of animals.

atmospheric oxygen
By measuring the oxidation of iron in pillow basalts from undersea volcanic eruptions, UC Berkeley scientists have more precisely dated the oxygenation of the deep ocean, inferring from that when oxygen levels in the atmosphere rose to current high levels.

The researchers found that the transition to a world with an oxygenated deep ocean occurred between 540 and 420 million years ago. They attribute this to an increase in atmospheric O2 to levels comparable to the 21 percent oxygen in the atmosphere today.

This inferred rise comes hundreds of millions of years after the origination of animals, which occurred between 700 and 800 million years ago.

“The oxygenation of the deep ocean and our interpretation of this as the result of a rise in atmospheric O2 was a pretty late event in the context of Earth history,” said Daniel Stolper, an assistant professor of earth and planetary science at UC Berkeley. “This is significant because it provides new evidence that the origination of early animals, which required O2 for their metabolisms, may have gone on in a world with an atmosphere that had relatively low oxygen levels compared to today.”

He and postdoctoral fellow Brenhin Keller will report their findings in a paper posted online Jan. 3 in advance of publication in the journal Nature. Keller is also affiliated with the Berkeley Geochronology Center.

The history of Earth’s oxygen

Oxygen has played a key role in the history of Earth, not only because of its importance for organisms that breathe oxygen, but because of its tendency to react, often violently, with other compounds to, for example, make iron rust, plants burn and natural gas explode.

Tracking the concentration of oxygen in the ocean and atmosphere over Earth’s 4.5-billion-year history, however, isn’t easy. For the first 2 billion years, most scientists believe very little oxygen was present in the atmosphere or ocean. But about 2.5-2.3 billion years ago, atmospheric oxygen levels first increased. The geologic effects of this are evident: rocks on land exposed to the atmosphere suddenly began turning red as the iron in them reacted with oxygen to form iron oxides similar to how iron metal rusts.

Earth scientists have calculated that around this time, atmospheric oxygen levels first exceeded about a hundred thousandth of today’s level (0.001 percent), but remained too low to oxygenate the deep ocean, which stayed largely anoxic.

By 400 million years ago, fossil charcoal deposits first appear, an indication that atmospheric O2 levels were high enough to support wildfires, which require about 50 to 70 percent of modern oxygen levels, and oxygenate the deep ocean. How atmospheric oxygen levels varied between 2,500 and 400 million years ago is less certain and remains a subject of debate.

“Filling in the history of atmospheric oxygen levels from about 2.5 billion to 400 million years ago has been of great interest given O2’s central role in numerous geochemical and biological processes. For example, one explanation for why animals show up when they do is because that is about when oxygen levels first approached the high atmospheric concentrations seen today,” Stolper said. “This explanation requires that the two are causally linked such that the change to near-modern atmospheric O2 levels was an environmental driver for the evolution of our oxygen-requiring predecessors.”

In contrast, some researchers think the two events are largely unrelated. Critical to helping to resolve this debate is pinpointing when atmospheric oxygen levels rose to near modern levels. But past estimates of when this oxygenation occurred range from 800 to 400 million years ago, straddling the period during which animals originated.

When did oxygen levels change for a second time?

Stolper and Keller hoped to pinpoint a key milestone in Earth’s history: when oxygen levels became high enough – about 10 to 50 percent of today’s level – to oxygenate the deep ocean. Their approach is based on looking at the oxidation state of iron in igneous rocks formed undersea (referred to as “submarine”) volcanic eruptions, which produce “pillows” and massive flows of basalt as the molten rock extrudes from ocean ridges. Critically, after eruption, seawater circulates through the rocks. Today, these circulating fluids contain oxygen and oxidize the iron in basalts. But in a world with deep-oceans devoid of O2, they expected little change in the oxidation state of iron in the basalts after eruption.

“Our idea was to study the history of the oxidation state of iron in these basalts and see if we could pinpoint when the iron began to show signs of oxidation and thus when the deep ocean first started to contain appreciable amounts of dissolved O2,” Stolper said.

To do this, they compiled more than 1,000 published measurements of the oxidation state of iron from ancient submarine basalts. They found that the basaltic iron only becomes significantly oxidized relative to magmatic values between about 540 and 420 million years ago, hundreds of millions of years after the origination of animals. They attribute this change to the rise in atmospheric O2 levels to near modern levels. This finding is consistent with some but not all histories of atmospheric and oceanic O2 concentrations.

“This work indicates that an increase in atmospheric O2 to levels sufficient to oxygenate the deep ocean and create a world similar to that seen today was not necessary for the emergence of animals,” Stolper said. “Additionally, the submarine basalt record provides a new, quantitative window into the geochemical state of the deep ocean hundreds of millions to billions of years ago.”

Source : UC Berkeley

Three Kinds of Information from a Single X-Ray Measurement

Whatever the size of mobile phones or computers are, the way in which such electronic devices operate relies on the interaction between various materials. For this reason, engineers as well as researchers need to know exactly how specific chemical elements inside a computer chip or a transistor diode behave, and what happens when these elements bond. Physicists of Friedrich Schiller University Jena, Germany, have now developed an innovative method that enables them to obtain several different types of information simultaneously from the interior of a nanoscale building block – and this while it is in the active state. The researchers from Jena and their partners have reported their findings in the current issue of the specialist journal “Science Advances”.

“Using our method, we can obtain information at one and the same time about the elements’ composition, that is to say the fraction between the elements; about their oxidation grade, which means their valence state or the nature of the bond; and finally about internal electrical fields that have thus been created,” explains Prof. Dr Carsten Ronning of the University of Jena. “These are all elementary indicators for the component’s function,” adds Ronning, who heads the project. However, in the procedure developed by the physicists from Jena, together with colleagues from Grenoble, Madrid and Vienna, the components to be investigated do not have to be elaborately prepared or possibly even destroyed. “In principle, we can X-ray the diodes of a mobile phone while it is switched on, without damaging it,” says Ronning.

X-ray beam from the particle accelerator

A decisive feature of the research approach is a very finely focussed X-ray beam, with which the Jena physicists initially X-rayed a device specially made for their experiments. “We introduced arsenic and gallium atoms into a silicon wire around 200 nanometres thick. When heated, these atoms agglomerate at one point, that is to say they mass together, which produces a functional component,” explains Prof. Ronning. “We then ran a 50-nanometre-wide X-ray beam along the wire, thus irradiating it bit by bit.” The researchers established that – such as in a solar cell – this arrangement mixture of materials converted the X-rays into electric current, which flowed only in one direction, as in a diode. In this way, the researchers made the internal electrical fields visible that are essential for the function of the component. In addition, the component emitted light. “The X-rays excite the atoms in the building block, which emit a characteristic radiation,” explains Dr Andreas Johannes, who conducted the experiments. “In this way we obtain a spectrum, which gives us valuable information about the individual elements present and their relative ratios.” If the energy of the X-rays is altered, so called X-ray absorption spectra are produced that enable researchers to make assertions regarding the oxidation grade of the elements – and by extension regarding the bonds themselves.

Obtain all these types of information through one measurement

“Now, it is possible to obtain all these types of information through one measurement by using our method,” says Andreas Johannes. Although comparable results are possible using electron microscopy, in these cases the devices have to be specially prepared and possibly destroyed, as the penetration depth of the electron beam is substantially more limited. Moreover, such measurements can only take place in a vacuum, whereas the X-ray method is virtually independent of any specific environment.

Up to now, such narrow X-ray beams can only be generated by particle accelerators, which is why the Jena University physicists have been working together closely with the European Synchrotron Radiation Facility (ESRF) in Grenoble, France, to develop the new measuring method. These facilities are available to both, scientific researchers and industry, in order to X-ray existing components with greater precision and, above all, to try out new combinations of materials in order to create better performing components. “For example, our method can be of value in developing new batteries,” says Andreas Johannes. “Because researchers would also like to examine these, especially while in use and fully operational, for example to determine the oxidation grades of the elements.”

Source : Friedrich-Schiller-Universität Jena

Neutron Spectroscopy Reveals Common ‘Oxygen Sponge’ Catalyst Soaks up Hydrogen Too

Having the right tool for the job enabled scientists at the Department of Energy’s Oak Ridge National Laboratory and their collaborators to discover that a workhorse catalyst of vehicle exhaust systems—an “oxygen sponge” that can soak up oxygen from air and store it for later use in oxidation reactions—may also be a “hydrogen sponge.”

The finding, published in the Journal of the American Chemical Society, may pave the way for the design of more effective catalysts for selective hydrogenation reactions. Selective hydrogenation is the key to producing valuable chemicals, for example, turning triple-bonded hydrocarbons called alkynes selectively into double-bonded alkenes—starting materials for the synthesis of plastics, fuels and other commercial products.

“Understanding how molecular hydrogen interacts with ceria [cerium oxide, CeO2], however, is a big challenge, as no regular technique can ‘see’ the light H atom. We turned to inelastic neutron spectroscopy, a technique that is very sensitive to hydrogen,” said ORNL chemist Zili Wu. At ORNL’s Spallation Neutron Source (SNS), a DOE Office of Science User Facility, a neutron beam line called VISION probed vibrational signals of atomic interactions and generated spectra describing them. “Because neutron spectroscopy could ‘see’ hydrogen due to its large neutron scattering cross-section, it succeeded where optical spectroscopy techniques failed and enabled the first direct observations of cerium hydrides both on the surface and in the bulk of a cerium oxide catalyst,” Wu said.

In vehicle engines, oxygen is needed for hydrocarbon fuel to burn. The exhaust that is generated contains deadly carbon monoxide and unburned hydrocarbons. In the catalytic converter, the catalyst cerium oxide grabs oxygen from air and adds it to carbon monoxide and hydrocarbons to turn them into carbon dioxide, which is nonlethal. The finding that cerium oxide may grab hydrogen as well as oxygen is promising for efforts to engineer it to catalyze both reactions that cause electron gain (“reduction” of a reactant) and electron loss (“oxidation”).

Two mechanisms have been proposed to explain the interaction between molecular hydrogen and cerium oxide. One suggests both hydrogen atoms associate only with oxygen atoms to produce the same product (two hydroxyl species, or OH chemical groups) on the surface. In the other mechanism posited, one hydrogen atom associates with an oxygen atom to make OH and the other hydrogen atom associates with a cerium atom to make cerium hydride (CeH). The former mechanism is termed “homolytic,” and the latter is called “heterolytic.”

“The heterolytic reaction had not been seen before on cerium oxide,” Wu said. “Theory predicted a heterolytic reaction, but there was no experimental proof.”

At the Center for Nanophase Materials Sciences (CNMS), a DOE Office of Science User Facility at ORNL, the researchers made nanoscale crystalline rods of cerium oxide with well-defined surface structure to facilitate an understanding of catalytic reactions that would be difficult with commercial, normally spherical particles of cerium oxide. The nanoscale rods allowed them to differentiate hydrogen in the bulk from hydrogen on the surface, where catalysis was presumed to happen. The first observation of hydrides both on the surface and in the bulk of ceria was important because it established that the bulk of the material also can participate in chemical reactions.

Also at CNMS, Wu and Guo Shiou Foo performed in situ experiments using infrared and Raman spectroscopies, which scatter photons to create spectra that give “fingerprints” of atomic vibrations. Unfortunately, these optical techniques “see” only vibrating oxygen–hydrogen bonds (from stretching between oxygen and hydrogen bonds); they are blind to hydride species on ceria. To see the hydrogen interactions directly, the researchers had to use SNS, where Yongqiang Cheng, Luke Daemen and Anibal Ramirez-Cuesta performed inelastic neutron scattering. Meanwhile, Franklin Tao, Luan Nguyen and Xiaoyan Zhang of the University of Kansas used ambient pressure X-ray photoelectron spectroscopy to characterize the oxidation state of cerium oxide, which was critical to deriving the mechanism. Moreover, Cheng, aided by Ariana Beste of the University of Tennessee, created theory-based simulations of vibrational spectra of neutrons and compared them with experimental observations. This teamwork was essential to providing a deeper understanding of the interaction between molecular hydrogen and cerium oxide-based catalysts.

The current neutron study used VISION to explore the nature of hydride species in the catalyst. Further studies will also employ another beam line, NOMAD, to characterize the exact structure of both the surface and bulk hydride in the catalyst to reveal, for example, if oxygen vacancies form channels in the bulk to bring in hydrogen and spur further hydride formation. What is more important, the researchers will take advantage of NOMAD’s ability to measure diffraction patterns at temperatures at which chemical reactions occur. Adding hydrocarbons, they will explore and reveal the catalytic role of the surface hydride versus the bulk hydride in hydrogenation reactions.

The understanding they build will facilitate the design of more effective cerium-based catalysts for diverse applications.

The title of the paper is “Direct Neutron Spectroscopy Observation of Cerium Hydride Species on a Cerium Oxide Catalyst.”

The DOE Office of Science supported the research. Computing resources were made available through ORNL’s Laboratory Directed Research and Development Program.

Source : Oak Ridge National Laboratory

EU Testing Way to Use Sun to Break up Plastics in Wastewater

While exposure to sunlight can degrade plastics into harmless elements, it’s a slow process. In some cases plastics can take several years to decompose. Joydeep Dutta, chair of theFunctional Materials division at KTH, says this system will speed up that process by making more efficient use of available visible light and ultraviolet rays from the Sun.

The system involves coatings with material of nano-sized semiconductors that initiate and speed up a natural process called photocatalytic oxidation, Dutta says. In a test household, these nano material coated filter systems will be placed at the exit of wastewater from homes. Similarly, in wastewater treatment plants these devices will be used to initiate microplastics degradation after the classical treatments are completed.

The photocatalytist membranes were created in partnership with the Swedish company, PP Polymer AB.

Photocatalytic oxidation with titanium oxide and zinc oxide semiconductors has been used toconvert volatile pollutants, oils and other substances  into harmless elements such as water and CO2. Similar in concept to photosynthesis, photocatalysis activates the breakup of compounds by exciting electrons, which then causes water molecules to split into their constituent parts, hydrogen and oxygen. The material captures enough solar radiation from a minimum of available light to set off a reaction with the molecules of the plastic. The radicals then exchange electrons with the atoms that comprise plastic molecules, effectively pulling these contaminants apart into harmless compounds of CO2 and water.

“The semiconductor material is able to excite the molecules and set off this process using the 40 percent of solar radiation that is visible light,” Dutta says.

Nearly every beach worldwide is reported to be contaminated by microplastics, according to the Norwegian Institute for Water Research. And, as if that weren’t bad enough, marine life ingest these plastics, which also adsorb pollutants such as DDT and PCB.

“These plastics will start accumulating in the food chain, transferring from species to species, with direct adverse consequences to human population,” Dutta says. “Tackling plastic pollution at its source is the most effective way to reduce marine litter.”

The project, titled Cleaning Litter by Developing and Applying Innovative Methods in European Seas (CLAIM), will also deploy floating booms at river mouths in Europe to collect visible plastic waste; and ferry routes in Denmark, the Gulf of Lyon, Ligurian Sea and Saronikos Gulf will be used to test a plastics measuring system that could be later deployed on shipping vessels.

Coordinated by the Hellenic Centre for Marine Research (HCMR) in Greece, CLAIM involves 19 partners from across 13 EU countries, as well as Tunisia and Lebanon. It is funded with a Horizon 2020 Innovative Action grant (grant agreement number: 774586 — CLAIM — H2020-BG-2016-2017/H2020-BG-2017-1). The project will commence in November 2017 and be completed in 2021.

Source : KTH Royal Institute of Technology

Discovery Lights Path for Alzheimer’s Research

A probe invented at Rice University that lights up when it binds to a misfoldedamyloid beta peptide — the kind suspected of causing Alzheimer’s disease — has identified a specific binding site on the protein that could facilitate better drugs to treat the disease.

Even better, the lab has discovered that when the metallic probe is illuminated, it catalyzes oxidation of the protein in a way they believe might keep it from aggregating in the brains of patients.

The study done on long amyloid fibrils backs up computer simulations by colleagues at the University of Miami that predicted the photoluminescent metal complex would attach itself to the amyloid peptide near a hydrophobic (water-avoiding) cleft that appears on the surface of the fibril aggregate. That cleft presents a new target for drugs.

Finding the site was relatively simple once the lab of Rice chemist Angel Martí used its rhenium-based complexes to target fibrils. The light-switching complex glows when hit with ultraviolet light, but when it binds to the fibril it becomes more than 100 times brighter and causes oxidation of the amyloid peptide.

Alzheimer
A rhenium-based complex developed at Rice University binds to fibrils of misfolded amyloid beta peptide, which marks the location of a hydrophobic cleft that could serve as a drug target, and oxidizes the fibril, which changes its chemistry in a way that could prevent further aggregation. Courtesy of the Marti Group

“It’s like walking on the beach,” Marti said. “You can see that someone was there before you by looking at footprints in the sand. While we cannot see the rhenium complex, we can find the oxidation (footprint) it produces on the amyloid peptide.

“That oxidation only happens right next to the place where it binds,” he said. “The real importance of this research is that allows us to see with a high degree of certainty where molecules can interact with amyloid beta fibrils.”

The study appears in the journal Chem.

“We believe this hydrophobic cleft is a general binding site (on amyloid beta) for molecules,” Martí said. “This is important because amyloid beta aggregation has been associated with the onset of Alzheimer’s disease. We know that fibrillar insoluble amyloid beta is toxic to cell cultures. Soluble amyloid oligomers that are made of several misfolded units of amyloid beta are also toxic to cells, probably even more than fibrillar.

“There’s an interest in finding medications that will quench the deleterious effects of amyloid beta aggregates,” he said. “But to create drugs for these, we first need to know how drugs or molecules in general can bind and interact with these fibrils, and this was not well-known. Now we have a better idea of what the molecule needs to interact with these fibrils.”

Alzheimer
A metallic probe lights up when it binds to a misfolded amyloid beta peptide in an experiment at Rice University. The probe identified a binding site that could facilitate better drugs to treat Alzheimer’s disease. Photo by Brandon Martin

When amyloid peptides fold properly, they hide their hydrophobic residues while exposing their hydrophilic (water-attracting) residues to water. That makes the proteins soluble, Martí said. But when amyloid beta misfolds, it leaves two hydrophobic residues, known as Valine 18 and Phenylalanine 20, exposed to create the hydrophobic cleft.

“It’s perfect, because then molecules with hydrophobic domains are driven to bind there,” Martí said. “They are compatible with this hydrophobic cleft and associate with the fibril, forming a strong interaction.”

If the resulting oxidation keeps the fibrils from aggregating farther into the sticky substance found in the brains of Alzheimer’s patients, it may be the start of a useful strategy to stop aggregation before symptoms of the disease appear.

“It’s a very attractive system because it uses light, which is a cheap resource,” Martí said. “If we can modify complexes so they absorb red light, which is transparent to tissue, we might be able to perform these photochemical modifications in living animals, and maybe someday in humans.”

Alzheimer
From left, Rice University research scientist Christopher Pennington, graduate student Bo Jiang and Angel Martí, an associate professor of chemistry and bioengineering, run an amyloid beta experiment in the Martí lab. Photo by Brandon Martin

He said light activation allows the researchers to have “exquisite control” of oxidation.

“We imagine it might be possible someday to prevent symptoms of Alzheimer’s by targeting amyloid beta in the same way we treat cholesterol in people now to prevent cardiovascular disease,” Martí said. “That would be wonderful.”

Rice alumnus Amir Aliyan, now a postdoctoral researcher at Tarbiat Modares University in Iran, is lead author of the paper. Co-authors are Rice graduate student Bo Jiang, Rice research scientist Christopher Pennington and, from the University of Miami, graduate students Thomas Paul and Gaurav Sharma and Rajeev Prabhakar, an associate professor of chemistry. Martí is an associate professor of chemistry and bioengineering at Rice.

The Welch Foundation and National Science Foundation supported the research. The Center of Computational Science at the University of Miami provided computational resources.

Source : Rice University

Building a Barrier Against Oxidation

Two-dimensional materials could underpin a novel family of flexible, low-power electronic devices, but their success depends on ensuring the layers are chemically stable. A*STAR researchers now show that one 2D material, phosphorene, can be stabilized with the right choice of substrate and an electric field.

Graphene, a single layer of carbon atoms, deserves its reputation as a supermaterial; it’s strong, hard, light, has excellent electronic and thermal properties. It is the archetypal 2D material. More recently scientists have created single layers of other materials — tin, germanium, boron, silicon and phosphorus — with their own signature properties. For example, while graphene is a semi-metal without a band gap, phosphorene is a semiconductor like silicon, which makes it useful for electronic devices. However, phosphorene has a notorious drawback: the material oxidizes in air and its quality is rapidly degraded.

In search of a viable approach to overcome this, Junfeng Gao and colleagues from the A*STAR Institute of High Performance Computing use first-principles calculations to demonstrate that placing phosphorene on a molybdenum diselenide substrate and applying a vertical electric field can drastically increase its resistance to oxidation.

“The interaction and charge transfer between substrate and phosphorene can be tuned by an external electric field, causing a change in surface activity and suppressing the oxidation of phosphorene,” explains Gao.

Their study shows that the dominant process involved in the degradation of phosphorene in air is the absorption of oxygen. The fast oxidation of freestanding phosphorene in ambient conditions is due to a low energy barrier for oxygen absorption of about 0.57 electronvolts: oxidation can occur in less than a minute.

When this analysis is repeated with phosphorene overlying molybdenum diselenide, the energy barrier is much higher. As well, the model shows that the presence of the molybdenum diselenide substrate enables more effective tuning of the properties of the phosphorene with an electric field. This increases the oxidation energy barrier even further. Under a suitable vertical electric field, the barrier can increase to 0.91 electronvolts. This lifetime of the phosphorene against oxidation can be 105 times greater than that without treatment.

Gao’s approach to achieve air-stable phosphorene may greatly promote its use in practical devices. “We will explore more substrates for their ability to stabilize phosphorene,” says Gao. “In particular, we want to find out if such a substrate is suitable for epitaxial growth of phosphorene.”

The A*STAR-affiliated researchers contributing to this research are from the Institute of High Performance Computing.

Source : A*STAR Research

Creating Longer-Lasting Fuel Cells

Fuel cells could someday generate electricity for nearly any device that’s battery-powered, including automobiles, laptops and cellphones. Typically using hydrogen as fuel and air as an oxidant, fuel cells are cleaner than internal combustion engines because they produce power via electrochemical reactions. Since water is their primary product, they considerably reduce pollution.

One issue that impacts the lifetime of the fuel cell is the oxidation, or breakdown, of its central electrolyte membrane. The process leads to formation of holes in the membrane and can ultimately cause a chemical short circuit.

An engineering team at Washington University in St. Louis has developed a new way to take a look at the rate at which oxidation occurs. Using fluorescence spectroscopy inside the fuel cell, they are able to probe the formation of the chemicals responsible for the oxidation, namely free radicals, during operation. The technique could be a game changer when it comes to understanding how the cells break down, and designing mitigation strategies that would extend the fuel cell’s lifetime.

fuel cells
Ramani

“If you buy a device — a car, a cell phone — you want it to last as long as possible,” said Vijay Ramani, the Roma B. and Raymond H. Wittcoff Distinguished Professor of Environment & Energy at the School of Engineering & Applied Science. “Unfortunately, components in a fuel cell can degrade, and it’s not an easy fix. What our new research does is really shed light on one of the modes by which these devices can fail, allowing us to figure out methods so we can improve the lifetime of devices that use these fuel cells.”

The research, published this summer in the journal ChemSusChem, is the first to utilize an in situ approach to examine the fuel cell’s inner membranes. A fluorescent dye is incorporated and used as a marker to ascertain the rate at which damaging free radicals are generated during operation.

“By using fluorescence spectroscopy in conjunction with an optical fiber, we can quantify the oxidative free radicals generated inside the fuel cell, which work to break down the membranes,” said Yunzhu Zhang, a doctoral candidate in Ramani’s lab, and study co-author.

Once they were able to observe the fuel cell’s inner workings, the researchers noticed that the weaker the light emitted from the fuel cell membrane, the greater the breakdown occurring from within.

“We can see this process occurring in real time,” said Shrihari Sankarasubramanian, a postdoctoral researcher who assisted with the project.

Until now, researchers examining fuel cell breakdown relied on the cell’s emissions to determine which chemical reactions might have been to blame for membrane breakdowns. They say this new approach allows them to focus on the factors taking place inside for a better assessment.

“Since the free radicals that cause the fuel cell membrane degradation are so short-lived, and the anion exchange membranes are so thin, our novel in situ approach is key to better study, understand and prevent the chemical breakdowns that is occurring during fuel cell operation,” said Javier Parrondo, a postdoctoral researcher and research co-author.

“The next step is to introduce antioxidant chemicals inside the fuel cell membranes, to see if they can reduce the rate at which these membranes break down,” Ramani said.

Source : Washington University in St. Louis

New Study on Graphene-Wrapped Nanocrystals Makes Inroads Toward Next-Gen Fuel Cells

A powdery mix of metal nanocrystals wrapped in single-layer sheets of carbon atoms, developed at the Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab), shows promise for safely storing hydrogen for use with fuel cells for passenger vehicles and other uses. And now, a new study provides insight into the atomic details of the crystals’ ultrathin coating and how it serves as selective shielding while enhancing their performance in hydrogen storage.

The study, led by Berkeley Lab researchers, drew upon a range of Lab expertise and capabilities to synthesize and coat the magnesium crystals, which measure only 3-4 nanometers (billionths of a meter) across; study their nanoscale chemical composition with X-rays; and develop computer simulations and supporting theories to better understand how the crystals and their carbon coating function together.

The science team’s findings could help researchers understand how similar coatings could also enhance the performance and stability of other materials that show promise for hydrogen storage applications. The research project is one of several efforts within a multi-lab R&D effort known as the Hydrogen Materials—Advanced Research Consortium (HyMARC) established as part of the Energy Materials Network by the U.S. Department of Energy’s Fuel Cell Technologies Office in the Office of Energy Efficiency and Renewable Energy.

Reduced graphene oxide (or rGO), which resembles the more famous graphene (an extended sheet of carbon, only one atom thick, arrayed in a honeycomb pattern), has nanoscale holes that permit hydrogen to pass through while keeping larger molecules at bay.

This carbon wrapping was intended to prevent the magnesium – which is used as a hydrogen storage material – from reacting with its environment, including oxygen, water vapor and carbon dioxide. Such exposures could produce a thick coating of oxidation that would prevent the incoming hydrogen from accessing the magnesium surfaces.

But the latest study suggests that an atomically thin layer of oxidation did form on the crystals during their preparation. And, even more surprisingly, this oxide layer doesn’t seem to degrade the material’s performance.

fuel cells
This rendering shows how hydrogen molecules dissociate into individual atoms on a thin oxide layer. Oxygen atoms are shown in red, magnesium atoms are shown in orange, and hydrogen atoms are shown in pink. (Credit: Berkeley Lab)

“Previously, we thought the material was very well-protected,” said Liwen Wan, a postdoctoral researcher at Berkeley Lab’sMolecular Foundry, a DOE Nanoscale Science Research Center, who served as the study’s lead author. The study was published in the Nano Letters journal. “From our detailed analysis, we saw some evidence of oxidation.”

Wan added, “Most people would suspect that the oxide layer is bad news for hydrogen storage, which it turns out may not be true in this case. Without this oxide layer, the reduced graphene oxide would have a fairly weak interaction with the magnesium, but with the oxide layer the carbon-magnesium binding seems to be stronger.

“That’s a benefit that ultimately enhances the protection provided by the carbon coating,” she noted. “There doesn’t seem to be any downside.”

David Prendergast, director of the Molecular Foundry’s Theory Facility and a participant in the study, noted that the current generation of hydrogen-fueled vehicles power their fuel cell engines using compressed hydrogen gas. “This requires bulky, heavy cylindrical tanks that limit the driving efficiency of such cars,” he said, and the nanocrystals offer one possibility for eliminating these bulky tanks by storing hydrogen within other materials.

The study also helped to show that the thin oxide layer doesn’t necessarily hinder the rate at which this material can take up hydrogen, which is important when you need to refuel quickly. This finding was also unexpected based on the conventional understanding of the blocking role oxidation typically plays in these hydrogen-storage materials.

That means the wrapped nanocrystals, in a fuel storage and supply context, would chemically absorb pumped-in hydrogen gas at a much higher density than possible in a compressed hydrogen gas fuel tank at the same pressures.

The models that Wan developed to explain the experimental data suggest that the oxidation layer that forms around the crystals is atomically thin and is stable over time, suggesting that the oxidation does not progress.

The analysis was based, in part, around experiments performed at Berkeley Lab’s Advanced Light Source (ALS), an X-ray source called a synchrotron that was earlier used to explore how the nanocrystals interact with hydrogen gas in real time.

Wan said that a key to the study was interpreting the ALS X-ray data by simulating X-ray measurements for hypothetical atomic models of the oxidized layer, and then selecting those models that best fit the data. “From that we know what the material actually looks like,” she said.

While many simulations are based around very pure materials with clean surfaces, Wan said, in this case the simulations were intended to be more representative of the real-world imperfections of the nanocrystals.

A next step, in both experiments and simulations, is to use materials that are more ideal for real-world hydrogen storage applications, Wan said, such as complex metal hydrides (hydrogen-metal compounds) that would also be wrapped in a protective sheet of graphene.

“By going to complex metal hydrides, you get intrinsically higher hydrogen storage capacity and our goal is to enable hydrogen uptake and release at reasonable temperatures and pressures,” Wan said.

Some of these complex metal hydride materials are fairly time-consuming to simulate, and the research team plans to use the supercomputers at Berkeley Lab’s National Energy Research Scientific Computing Center (NERSC) for this work.

“Now that we have a good understanding of magnesium nanocrystals, we know that we can transfer this capability to look at other materials to speed up the discovery process,” Wan said.

The Advanced Light Source, Molecular Foundry, and National Energy Research Scientific Computing Center are DOE Office of Science User Facilities.

This work was supported by the U.S. Department of Energy’s Office of Energy Efficiency and Renewable Energy’s Fuel Cell Technologies Office.

Source : Lawrence Berkeley National Laboratory

Clay Minerals and Metal Oxides Change How Uranium Travels Through Sediments

The Science

Clay minerals are ubiquitous natural components of sediments and soils. Also, clays are used in the engineered barriers of spent nuclear fuel storage facilities. Scientists examined the molecular form of uranium(IV) in the presence of montmorillonite clays. The team found that the clays could inhibit the predicted precipitation of the mineral uraninite.

The Impact

The effect of clays on uranium is not part of computational models of uranium transport in the environment. That’s a problem when studying how uranium will spread from a mine or storage site. Using state-of-the-art spectroscopy techniques, scientists provided a molecular-level view of uranium. The information is vital to accurately predict uranium’s travels through the subsurface.

Summary

Uranium mobility in the subsurface depends strongly on its oxidation state, with uranium(IV) being significantly less soluble than uranium(VI). However, solubility also depends on the contaminant’s molecular form, which can be affected by adsorption onto the surface of minerals, bacterial membranes and other constituents in the environment it is traveling through. Researchers examined the ability of montmorillonite clay minerals to adsorb uranium(IV) resulting from the reduction of uranium(VI) and compared it to that of iron and titanium oxide surfaces. The team tracked the valence and molecular structure of the uranium using synchrotron x-ray absorption spectroscopy. The team’s findings showed that at low clay surface:uranium ratios, the reduction of uranium(VI) in the presence of SYn-1 montmorillonite leads to the formation of the mineral uraninite (UO2). However, at high clay surface:uranium ratios (more typical of environmental conditions), a significant fraction of the resulting uranium(IV) is present as adsorbed uranium(IV) ions (up to 50 percent of total uranium). The threshold uranium(IV) surface coverage above which uraninite formation begins was determined to be significantly lower for montmorillonite than for iron or titanium oxides, suggesting that metal oxides may play a more important role than clay minerals in stabilizing the non-uraninite species observed in natural sediments.

Source : U.S. Department of Energy

New Technologies for Vinasse Storage and Transportation Reduce Methane Emissions

New technologies used by sugar mills to transport and store vinasse have reduced greenhouse gas emissions during the process of producing ethanol from sugarcane.

This is the main finding of a study performed by researchers at the University of São Paulo’s Center for Nuclear Energy in Agriculture (CENA-USP) and Luiz de Queiroz College of Agriculture (ESALQ), Brazil, in collaboration with colleagues at the National Bioethanol Science & Technology Laboratory (CTBE).

The results of the study, which was supported by FAPESP, were published in the journal Atmospheric Environment.

“The ethanol industry has introduced new technologies for the transportation and storage of vinasse, contributing to a reduction in the emission of methane [the main greenhouse gas produced by the residue],” said Bruna Gonçalves de Oliveira, a postdoctoral fellow at the Agronomy Institute (IAC) with a fellowship from FAPESP and first author of the study.

The researchers quantified methane emissions from the two main systems that mills currently use to transport and store vinasse, a liquid residue formed during the distillation of sugarcane molasses to produce ethanol. The traditional system consists of open channels, which may or may not be lined. A new method comprises closed tanks and pipes.

An analysis of comparative data showed that emissions from open channels were 620 times greater than emissions from closed tanks and pipes.

“The difference is due to the characteristics of the transportation and storage system consisting of tanks and pipes,” Oliveira toldAgência FAPESP. “Transporting vinasse from one tank to another in high-pressure pipes tends to oxygenate the residue, modifying the anaerobic conditions [lack of oxygen] and making them favorable for the production of methane.”

Evolution

According to Oliveira, whose PhD research at CENA-USP was also supported by a fellowship from FAPESP, 13 liters of vinasse are produced on average per liter of ethanol manufactured from sugarcane.

To reduce the environmental impact of vinasse, which contains high concentrations of organic matter, potassium and sulfates, the Brazilian ethanol industry decided some 30 years ago that the cheapest and simplest solution would be to recycle the vinasse for use as a fertilizer on irrigated sugarcane plantations.

To store vinasse and transport it to plantations, the mills initially used a system of open channels lined with plastic, cement or concrete, along which the residue is transported by gravity and then pumped to cane fields.

However, Oliveira noted, the amounts of greenhouse gases (GHGs), such as methane, emitted by the vinasse during storage and transportation had never been quantified and are not included in the ethanol industry’s GHG inventories.

“The industry’s GHG inventories take into account only emissions from the use of vinasse in fertirrigation,” she said.

During her master’s research supervised by Brigitte Josefine Feigl, a researcher at CENA-USP and a principal investigator for the project, Oliveira quantified methane emissions from vinasse after it left the distillery in a 40-km open channel, which was mostly unlined (a small stretch was lined with cement).

The analysis showed that 98% of the total emissions of methane and other GHGs from vinasse occurred during storage and transportation via this system of open channels.

Nitrogen emissions in the field during fertirrigation with vinasse are accounted for by GHG inventories, but we found that these emissions contributed to only 2% of total emissions,” Oliveira said.

Comparison of systems

In compliance with rules issued by the CETESB, São Paulo State’s environmental regulator, sugar plants in the state began lining most of the open channels used to transport vinasse to prevent the residue from infiltrating the soil and contaminating the water table.

Some plants, such as those Oliveira studied during her PhD research, switched to underground tanks and pipes as a more sustainable solution.

No research had ever been conducted to evaluate whether these improvements could alter the conditions for methane production and significantly reduce GHG emissions during ethanol production.

“Our goal was to find out how advances in vinasse storage and transportation technology affected GHG emissions,” Oliveira said.

In pursuit of this goal, from 2012-13 (a period corresponding to two harvests), the researchers monitored methane emissions from the vinasse storage and transportation systems used by two sugar mills in the Piracicaba and Bauru regions of São Paulo State.

One used open channels measuring 1.5 m in width, 0.6 m in depth and 60 km in length, of which 40 km were cement lined. In the 20 km of unlined channels, vinasse came into direct contact with the soil.

The other mill used a system comprising ten polyethylene-lined tanks that pumped vinasse at a high speed to sugarcane plantations through pipelines.

The analysis showed that in general, the intensity of methane emissions was approximately 1.36 kg of CO2 equivalent per cubic meter of vinasse transported in open channels, 620 times greater than the emissions from vinasse stored in tanks and transported by pipelines.

Roughly 80% of the methane emissions from the open channel system came from the unlined section.

“Vinasse supplies nutrients and ideal anaerobic conditions and temperatures for soil microorganisms in the vicinity of the unlined channels to emit methane. This doesn’t happen in the system of tanks and pipelines,” Oliveira said.

In closed systems, the vinasse reaches a temperature of 60 °C, which inhibits microbiological activity. In addition, the residue is pumped at a high pressure, which reduces decantation to the bottom of the tanks and methane-producing decomposition by microorganisms.

The high pressure at which vinasse is pumped in the system of closed tanks and pipes also oxygenates the residue, diminishing anaerobic conditions for microorganisms to produce methane (methanogenesis).

“Oxygenation limits the potential for vinasse redox [oxidation and reduction] and anaerobiosis. Methanogenic microbial activity is therefore limited or even non-existent, reducing methane emissions,” Oliveira said.

Based on these findings, the researchers concluded that systems of tanks and pipes for vinasse storage and transportation could effectively mitigate methane emissions during the production of ethanol from sugarcane.

They also concluded that the use of new technologies, combined with improvements to vinasse storage and distribution systems, would significantly reduce GHG emissions.

“In addition to these factors altogether, a number of innovations that the sugar and fuel ethanol industry is starting to introduce, such as vinasse concentration and biodigestion, will reduce GHG emissions even further, so that ethanol from sugarcane can become an even cleaner and more sustainable biofuel,” Oliveira said.

Source : By Elton Alisson  |  Agência FAPESP

A New Oxidation State for Plutonium

The Science

Associated with nuclear power and national security, plutonium (Pu) has some of the most complicated chemistry on the periodic table. For the first time, scientists showed a new oxidation state (electron arrangement) for element 94. They achieved this result by adding electrons to a specific plutonium-containing molecule, an organometallic Pu3+-containing complex. They then studied the results. The results included a complex containing Pu2+. The Pu2+ was bound to carbon in the complex. This is the first example of plutonium (Pu2+) bonding to carbon in the literature.

The Impact

An oxidation state of an element is one of the most influential properties. It dictates chemical behavior, bonding, and reactivity. Because of this importance, scientists have heavily studied the range of accessible oxidation states for all the elements. They generally presumed that all possibilities were already defined. Discovery of a new oxidation state represents a significant breakthrough in the fundamental chemistry of plutonium. This work could lead to development of new bonding types and reactivity patterns. The results offer insights for security and energy production.

Summary

The researchers synthesized a Pu(III) starting material, PuCp”3 (Cp” = the substituted anionic cyclopentadienyl ring [C5H3(SiMe3)2-1,3-]–), and characterized it by single crystal X-ray diffraction to reveal the first structural information on Pu–C bonds. Subsequent reduction with potassium graphite (in the presence of 2.2.2.-cryptand to encapsulate the K+ ion) affords [K(cryptand)][PuIICp”3], which formally contains a Pu2+ ion, never before isolated and verified in molecular form. The compound is highly sensitive to oxygen and water (which very rapidly re-oxidize the plutonium back to the +3 state). In the analogous La2+, Th2+ and U2+ systems, stabilization of the 5d or 6d orbitals by the C3 symmetric arrangement of the Cp” ligands affords fnd1 (La, U) or d2 (Th) electron configurations. In contrast, computational analyses of the Pu2+ molecule, in conjunction with ultraviolet/visible/near infrared spectroscopic data, indicate an electronic picture best described as predominately 5f66d0 with a low-lying (and possibly thermally accessible) 5f56d1 state. The results demonstrate that plutonium is likely a crossover element in the actinide series at which point a pure 5fn+1 configuration becomes more stable for the +2 cations than configurations containing 6d character.

Source : U.S. Department of Energy

Mainz-Based Researchers Stabilized Gold in Very Rare Oxidation State +II

According to text book knowledge, the usual oxidation states of gold in compounds are +I and +III. The divalent form (+II), on the other hand, prefers to form polynuclear compounds or simply undergoes transformation into the mono- and trivalent forms. However, the elements next to gold in the periodic table are quite different in this respect. The ions of the coinage metals, copper(+II) and silver(+II), are usually present in divalent form and this is also the case for gold’s neighbors to its left and right, platinum(+II) and mercury(+II). It has been postulated that when gold undergoes photochemical catalysis reactions, the +II state may form, but definitive evidence has not been provided to date. The corresponding proof has just been advanced by researchers at Johannes Gutenberg University Mainz (JGU) in a recent publication.

A team of chemists led by Professor Katja Heinze at the Institute of Inorganic Chemistry and Analytical Chemistry of JGU has been able to isolate and analyze gold in the very rare oxidation state +II. This provides the missing links in the homologous series of the coinage metal ions copper(+II), silver(+II), gold(+II), and in the ‘relativistic’ triad of platinum(+II), gold(+II), and mercury(+II). “Fundamental data unknown to date such as ion size, preferred structural arrangement, and the reactivity of gold(+II) have now been made available,” explained Sebastian Preiß, doctoral candidate in Heinze’s team, who was able to isolate the gold(+II) complex in its pure form for the first time. The findings have been published in Nature Chemistry.

The stabilization of the very labile gold(+II) ion was achieved by the researchers with the help of a so-called porphyrin used to encapsulate the gold(+II) ion. In combination with magnesium or iron ions in the center, respectively, the porphyrin macrocycle is present in the green pigment of plants (chlorophyll), and in the red pigment of the blood (heme). With gold(+II) at its center, porphyrin blocks the normal reaction pathways of gold(+II), i.e., the formation of polynuclear compounds or the conversion to the more stable gold(+I) and gold(+III) complexes. “This enabled for the first time to investigate this unique class of stable mononuclear gold(+II) complexes and to describe them comprehensively,” summarized Professor Katja Heinze. Interestingly, the arrangement of the four atoms next to the gold(+II) ion is not square planar with the atoms placed at equal distances to the gold as in the case of the corresponding structures of gold’s neighboring elements copper(+II), silver(+II), platinum(+II), and mercury(+II). Instead, the structure shows a rhombic distortion with two short and two long distances. In technical terms, this previously unobserved phenomenon in the case of gold(+II) ions can be attributed to a second-order Jahn-Teller effect caused by the relativistic properties of gold.

Since this new gold(+II) compound can also be prepared from the gold(+III) complex present in potent anti-cancer agents, the researchers tried to find out whether the gold(+II) porphyrin also plays a role in biological systems. They discovered that the gold(+II) complex can be generated under near physiological conditions from a cytostatic gold(+III) agent. On exposure to atmospheric oxygen, the gold(+II) porphyrin forms reactive oxygen species (ROS), which are known to induce apoptosis, or programmed cell death. “We thus have a plausible functional chain starting with a cytostatic agent and leading to targeted cell death with the gold(+II) porphyrin acting as an important link in the chain,” emphasized Professor Katja Heinze. “A major impetus for us to continue with research in this field is that curiosity-driven fundamental research about unusual species enabled us to reach insights that could well be relevant to medical applications,” concluded Heinze.

Source : Johannes Gutenberg-Universität Mainz

Smart Materials for Extreme Loads

The inner wall of future fusion reactors is subjected to extreme heat flux densities comparable to those on the outer wall of space ships when they enter the earth’s atmosphere again. In addition, there are intensive particle and neutron fluxes which lead to material erosion and defects. Among other things, because of its high melting point, tungsten is regarded as the preferred wall material. However, its brittleness and the high oxidation rate in the event of an extraordinary air intake at high temperatures are problematic. The scientists at Jülich Research Center, together with national and international partners, have developed new, smart material concepts based on tungsten: fiber-reinforced composites, which reduce the spread of harmful cracks, as well as smart alloys of tungsten, chromium and the light metal yttrium W-Cr-Y), which show an approximately 100,000-fold reduced oxidation rate compared to pure tungsten.

After successful development, characterization and production of material samples, research on smart tungsten materials has now entered a second, decisive phase – the qualification of materials under fusion-type stress scenarios. These are carried out at the Forschungszentrum Jülich at special test facilities: electron beam systems for thermal melt tests as well as linear plasma systems and laser systems for combined particle and thermal stress. First measurements on material samples in the PSI-2 linear plasma system with thin layers of W-Cr-Y have shown that the tungsten alloy is similarly resistant to material erosion compared to pure tungsten reference samples. The initial reduction in the oxidation capacity is also retained after plasma loading. This demonstrates the basic suitability of the smart alloy for use in fusion systems.

A next, important step towards the development of a smart wall concept for the fusion reactor has already been done: research partners at the Belgian institute SCK-CEN in Mol have begun to investigate the emission of tungsten with neutrons by means of a European research project. In approximately one and a half years, new stress tests can then be carried out at the Jülich Research Center on the newly produced material samples produced in this way.

Original Publication:

A. Katz, A. Katzer, A. Katzer, A. Katzer, A. Katzer, A. Katzer, A. Katzel, and others N. Orda
Smart alloys for a future FusionPowerSystem: First studies underneathPlastic load and in accidental conditions
Nuclear Materials and Energy (2016), DOI: 10.1016 / j.nme.2016.11.015

Source : Forschungszentrum Jülich

Chances of Hypersonic Travel Heat up with New Materials Discovery

hypersonic aerospace vehiclesResearchers at The University of Manchester in collaboration with Central South University (CSU), China, have created a new kind of ceramic coating that could revolutionise hypersonic travel for air, space and defense purposes.

Hypersonic travel means moving at Mach five or above, which is at least five times faster than the speed of sound. When moving at such velocity the heat generated by air and gas in the atmosphere is extremely hot and can have a serious impact on an aircraft or projectile’s structural integrity. That is because he temperatures hitting the aircraft can reach anywhere from 2,000 to 3,000 °C.

The structural problems are primarily caused by processes called oxidation and ablation. This is the when extremely hot air and gas remove surface layers from the metallic materials of the aircraft or object travelling at such high speeds. To combat the problem materials called ultra-high temperature ceramics (UHTCs) are needed in aero-engines and hypersonic vehicles such as rockets, re-entry spacecraft and defence projectiles.

But, at present, even conventional UHTCs can’t currently satisfy the associated ablation requirements of travelling at such extreme speeds and temperatures. However, the researchers at The University of Manchester’s and the Royce Institute, in collaboration with the Central South University of China, have designed and fabricated a new carbide coating that is vastly superior in resisting temperatures up to 3,000 °C, when compared to existing UHTCs.

Professor Philip Withers, Regius Professor from The University of Manchester, says: “Future hypersonic aerospace vehicles offer the potential of a step jump in transit speeds. A hypersonic plane could fly from London to New York in just two hours and would revolutionise both commercial and commuter travel.

“But at present one of the biggest challenges is how to protect critical components such as leading edges, combustors and nose tips so that they survive the severe oxidation and extreme scouring of heat fluxes at such temperatures cause to excess during flight.”

hypersonic aerospace vehiclesFuture hypersonic aerospace vehicles offer the potential of a step jump in transit speeds. A hypersonic plane could fly from London to New York in just two hours and would revolutionise both commercial and commuter travel.

Professor Philip Withers

So far, the carbide coating developed by teams in both University of Manchester and Central South University is proving to be 12 times better than the conventional UHTC, Zirconium carbide (ZrC). ZrC is an extremely hard refractory ceramic material commercially used in tool bits for cutting tools.

The much improved performance of the coating is due to its unique structural make-up and features manufactured at the Powder Metallurgy Institute, Central South University and studied in University of Manchester, School of Materials. This includes extremely good heat resistance and massively improved oxidation resistance.

What makes this coating unique is it has been made using a process called reactive melt infiltration (RMI), which dramatically reduces the time needed to make such materials, and has been in reinforced with carboncarbon composite (C/C composite). This makes it not only strong but extremely resistant to the usual surface degradation.

Professor Ping Xiao, Professor of Materials Science, who led the study in University of Manchester explains: “Current candidate UHTCs for use in extreme environments are limited and it is worthwhile exploring the potential of new single-phase ceramics in terms of reduced evaporation and better oxidation resistance. In addition, it has been shown that introducing such ceramics into carbon fibre- reinforced carbon matrix composites may be an effective way of improving thermal-shock resistance.”

Advanced Materials

Advanced materials is one of The University of Manchester’s research beacons – examples of pioneering discoveries, interdisciplinary collaboration and cross-sector partnerships that are tackling some of the biggest questions facing the planet.

Source : University of Manchester

Manipulating Earth-Abundant Materials to Harness the Sun’s Energy

The Science

Depositing one layer of atoms at a time can result in materials that greatly improve fuel cells, batteries and other devices. In this research, scientists precisely added chromium to iron oxides to control the electronic and optical properties. The result was a highly ordered thin film of chromium ferrite (Fe2CrO4). Chromium ferrite becomes more electrically conductive by absorbing light.  The material could be useful for vital solar processes, such as water splitting to make hydrogen for fuel, coolants and more.

The Impact

The research offers insights on how to design and make materials with new performance characteristics. For example, scientists could use the unexpected optical properties of chromium ferrite films to produce hydrogen from water and sunlight. Hydrogen is vital in chemical and petroleum industries and as a coolant. Further, hydrogen is increasingly popular as a fuel for transportation or in the generation of electricity.

Summary

In this research, scientists used molecular beam epitaxy to deposit precisely determined quantities of iron (Fe), chromium (Cr) and oxygen (O) atoms to make materials that were predicted to have various degrees of electrical conductivity, ranging from highly conductive to electrically insulating. The investigators made Fe3O4 (a half-metal), Fe2CrO4 (a semiconductor) and FeCr2O4 (an insulator). This study clarified the conductive properties of these iron chromium oxides, showing how the positions of the elements in the crystal lattice, oxidation state or charge (for the cations), and the ability of the electrons to move within the structure resulted in their respective conductive properties. The structure of Fe2CrO4was shown to be a spinel, having Fe in the tetrahedral positions, but both Cr and Fe in the octahedral positions. The Fe was found to be in one of two oxidation states, +2 or +3, but Cr was found to have only a +3 charge. As a result, electrons could hop between Fe cations at tetrahedral and octahedral sites. However, the team found the conductivity to be lower than that in Fe3O4, where electrons can freely hop between Fe2+ and Fe3+ on octahedral sites. In the case of FeCr2O4, Fe is only present as a 2+ cation. As a result, there is no way for electrons to hop from Fe to Fe, and the material is an electrical insulator. The team showed that Fe2CrO4 absorbs visible light leading to enhanced electrical conductivity, or photoconductivity. The optical and electronic properties of Fe2CrO4 suggest that this material could be useful for important solar photoelectrochemical processes such as water splitting.

Source : U.S. Department of Energy