Hydrocarbons deep within Earth: New computational study reveals how

A new computational study published in the Proceedings of the National Academy of Sciences reveals how hydrocarbons may be formed from methane in deep Earth at extreme pressures and temperatures.

The thermodynamic and kinetic properties of hydrocarbons at high pressures and temperatures are important for understanding carbon reservoirs and fluxes in Earth.

The work provides a basis for understanding experiments that demonstrated polymerization of methane to form high hydrocarbons and earlier methane forming reactions under pressure.

Hydrocarbons (molecules composed of the elements hydrogen and carbon) are the main building block of crude oil and natural gas. Hydrocarbons contribute to the global carbon cycle (one of the most important cycles of Earth that allows for carbon to be recycled and reused throughout the biosphere and all of its organisms).

The team includes colleagues at UC Davis, Lawrence Livermore National Laboratory and Shell Projects & Technology. One of the researchers, UC Davis Professor Giulia Galli, is the co-chair of the Deep Carbon Observatory's Physics and Chemistry of Deep Carbon Directorate and former LLNL researcher.

Geologists and geochemists believe that nearly all (more than 99 percent) of the hydrocarbons in commercially produced crude oil and natural gas are formed by the decomposition of the remains of living organisms, which were buried under layers of sediments in Earth's crust, a region approximately 5-10 miles below Earth's surface.

But hydrocarbons of purely chemical deep crustal or mantle origin (abiogenic) could occur in some geologic settings, such as rifts or subduction zones said Galli, a senior author on the study.

"Our simulation study shows that methane molecules fuse to form larger hydrocarbon molecules when exposed to the very high temperatures and pressures of the Earth's upper mantle," Galli said. "We don't say that higher hydrocarbons actually occur under the realistic 'dirty' Earth mantle conditions, but we say that the pressures and temperatures alone are right for it to happen.

Galli and colleagues used the Mako computer cluster in Berkeley and computers at Lawrence Livermore to simulate the behavior of carbon and hydrogen atoms at the enormous pressures and temperatures found 40 to 95 miles deep inside Earth. They used sophisticated techniques based on first principles and the computer software system Qbox, developed at UC Davis.

They found that hydrocarbons with multiple carbon atoms can form from methane, (a molecule with only one carbon and four hydrogen atoms) at temperatures greater than 1,500 K (2,240 degrees Fahrenheit) and pressures 50,000 times those at Earth's surface (conditions found about 70 miles below the surface).

"In the simulation, interactions with metal or carbon surfaces allowed the process to occur faster -- they act as 'catalysts,' " said UC Davis' Leonardo Spanu, the first author of the paper.

The research does not address whether hydrocarbons formed deep in Earth could migrate closer to the surface and contribute to oil or gas deposits. However, the study points to possible microscopic mechanisms of hydrocarbon formation under very high temperatures and pressures.

Galli's co-authors on the paper are Spanu; Davide Donadio at the Max Planck Institute in Meinz, Germany; Detlef Hohl at Shell Global Solutions, Houston; and Eric Schwegler of Lawrence Livermore National Laboratory.

Story Source:

The above story is reprinted (with editorial adaptations) from materials provided by DOE/Lawrence Livermore National Laboratory.

Journal Reference:

L. Spanu, D. Donadio, D. Hohl, E. Schwegler, G. Galli. Stability of hydrocarbons at deep Earth pressures and temperatures. Proceedings of the National Academy of Sciences, 2011; DOI: 10.1073/pnas.1014804108

New elastic material changes color in UV light

Researchers from North Carolina State University have created a range of soft, elastic gels that change color when exposed to ultraviolet (UV) light -- and change back when the UV light is removed or the material is heated up.

The gels are impregnated with a type of photochromic compound called spiropyran. Spiropyrans change color when exposed to UV light, and the color they change into depends on the chemical environment surrounding the material.

The researchers made the gels out of an elastic silicone substance, which can be chemically modified to contain various other chemical compounds -- changing the chemical environment inside the material. Changing this interior chemistry allows researchers to fine-tune how the color of the material changes when exposed to UV light.

"For example, if you want the material to turn yellow when exposed to UV light, you would attach carboxylic acid," explains Dr. Jan Genzer, Celanese Professor of Chemical and Biomolecular Engineering at NC State and co-author of a paper describing the research. "If you want magenta, you'd attach hydroxyl. Mix them together, and you get a shade of orange."

Photochromic compounds are not new, but this is the first time they've been incorporated into an elastic material, without impairing the material's elasticity.

The researchers were also able to create patterns by using a shaped mold to change the chemical make-up of specific regions in the material. For example, applying hydroxyl around a star-shaped mold (like a tiny cookie cutter) on the material would result in a yellow star-shaped pattern appearing on a dark magenta elastic when it is exposed to UV light.

"There are surely applications for this material -- it's flexible, changes color in UV light, reverts to its original color in visible light, and can be patterned," Genzer says. "At this stage we have not identified the best application yet."

Story Source:

The above story is reprinted (with editorial adaptations) from materials provided by North Carolina State University.

Journal Reference:

Hyun-Kwan Yang, A. Evren Ozcam, Kirill Efimenko and Jan Genzer. Photochromic materials with tunable color and mechanical flexibility. Soft Matter, April 2011

New way to control magnetic properties of graphene discovered

University of Maryland researchers have discovered a way to control magnetic properties of graphene that could lead to powerful new applications in magnetic storage and magnetic random access memory.

The finding by a team of Maryland researchers, led by Physics Professor Michael S. Fuhrer of the UMD Center for Nanophysics and Advanced Materials is the latest of many amazing properties discovered for graphene.

A honeycomb sheet of carbon atoms just one atom thick, graphene is the basic constituent of graphite. Some 200 times stronger than steel, it conducts electricity at room temperature better than any other known material (a 2008 discovery by Fuhrer, et. al). Graphene is widely seen as having great, perhaps even revolutionary, potential for nanotechnology applications. The 2010 Nobel Prize in physics was awarded to scientists Konstantin Novoselov and Andre Geim for their 2004 discovery of how to make graphene.

In their new graphene discovery, Fuhrer and his University of Maryland colleagues have found that missing atoms in graphene, called vacancies, act as tiny magnets -- they have a "magnetic moment." Moreover, these magnetic moments interact strongly with the electrons in graphene which carry electrical currents, giving rise to a significant extra electrical resistance at low temperature, known as the Kondo effect. The results appear in the paper "Tunable Kondo effect in graphene with defects" published this month in Nature Physics.

The Kondo effect is typically associated with adding tiny amounts of magnetic metal atoms, such as iron or nickel, to a non-magnetic metal, such as gold or copper. Finding the Kondo effect in graphene with vacancies was surprising for two reasons, according to Fuhrer.

"First, we were studying a system of nothing but carbon, without adding any traditionally magnetic impurities. Second, graphene has a very small electron density, which would be expected to make the Kondo effect appear only at extremely low temperatures," he said.

The team measured the characteristic temperature for the Kondo effect in graphene with vacancies to be as high as 90 Kelvin, which is comparable to that seen in metals with very high electron densities. Moreover the Kondo temperature can be tuned by the voltage on an electrical gate, an effect not seen in metals. They theorize that the same unusual properties of that result in graphene's electrons acting as if they have no mass also make them interact very strongly with certain kinds of impurities, such as vacancies, leading to a strong Kondo effect at a relatively high temperature.

Fuhrer thinks that if vacancies in graphene could be arranged in just the right way, ferromagnetism could result. "Individual magnetic moments can be coupled together through the Kondo effect, forcing them all to line up in the same direction," he said.

"The result would be a ferromagnet, like iron, but instead made only of carbon. Magnetism in graphene could lead to new types of nanoscale sensors of magnetic fields. And, when coupled with graphene's tremendous electrical properties, magnetism in graphene could also have interesting applications in the area of spintronics, which uses the magnetic moment of the electron, instead of its electric charge, to represent the information in a computer.

"This opens the possibility of 'defect engineering' in graphene -- plucking out atoms in the right places to design the magnetic properties you want," said Fuhrer.

This research was supported by grants from the National Science Foundation and the Office of Naval Research.

Story Source:

The above story is reprinted (with editorial adaptations ) from materials provided by University of Maryland.

Journal Reference:

Jian-Hao Chen, Liang Li, William G. Cullen, Ellen D. Williams, Michael S. Fuhrer. Tunable Kondo effect in graphene with defects. Nature Physics, 2011; DOI: 10.1038/nphys1962

Toward a more efficient use of solar energy

The exploitation and utilization of new energy sources are considered to be among today's major challenges. Solar energy plays a central role, and its direct conversion into chemical energy, for example hydrogen generation by water splitting, is one of its interesting variants. Titanium oxide-based photocatalysis is the presently most efficient, yet little understood conversion process. In cooperation with colleagues from Germany and abroad, scientists of the KIT Institute for Functional Interfaces (IFG) have studied the basic mechanisms of photochemistry by the example of titania and have presented new detailed findings.

Even though hydrogen production from water and sunlight by means of oxide powders has been studied extensively for several decades, the basic physical and chemical mechanisms of the processes involved cannot yet be described in a satisfactory way. Together with colleagues from the universities of St. Andrews (Scotland) and Bochum and Helmholtz-Forschungszentrum Berlin, scientists at KIT's Institute for Functional Interfaces, headed by Professor Christof Wöll, have succeeded in gathering new findings on the fundamental mechanisms of photochemistry on titanium dioxide (TiO2).

Titanium dioxide, or titania, is a photoactive material occurring in nature in the rutile and anatase modifications, the latter of which being characterized by a ten times higher photochemical activity. When the white TiO2 powder, which is also used as a pigment in paints and sunscreens, is exposed to light, electrons are excited and can, for example, split water into its components oxygen and hydrogen. The hydrogen produced in that way is a "clean" energy source: No climate-killing greenhouse gases are generated but only water is produced during combustion. Titanium dioxide is also used to manufacture self-cleaning surfaces from which unwanted films are removed through photochemical processes triggered by incident sunlight. In hospitals, this effect is used for sterilizing specially coated instruments by means of UV irradiation.

So far, the physical mechanisms of these photochemical reactions on titania surfaces and especially the reason for the much higher activity of anatase could not be explained. The powder particles used in photoreactors are as tiny as a few nanometers only and are thus too small for use in studies by means of the powerful methods of surface analysis. By using instead mm-sized single-crystal substrates, the researchers were for the first time able to precisely study photochemical processes on the surface of titanium dioxide by means of a novel infrared spectrometer.

Using a laser-based technique, the scientists, in addition, determined the lifetime of light-induced electronic excitations inside the TiO2 crystals. According to Professor Christof Wöll, Head of the IFG, exact information about these processes is of great importance: "A short lifetime means that the excited electrons fall back again at once: We witness some kind of an internal short circuit. In the case of a long lifetime, the electrons remain in the excited state long enough to be able to reach the surface of the crystal and to induce chemical processes." Anatase is particularly well suited for the latter purpose because it is provided with a special electronic structure that prevents "internal short circuits."

Knowledge of this feature will allow the researchers to further optimize shape, size, and doping of anatase particles used inside photoreactors. The objective is to develop photoactive materials with higher efficiencies and longer lifetimes: "The results obtained by Professor Wöll and his co-workers are of great importance regarding the generation of electrical and chemical energy from sunlight, and especially regarding the optimization of photoreactors," says Professor Olaf Deutschmann, spokesman of the Helmholtz Research Training Group on "Energy-related Catalysis."

Story Source:

The above story is reprinted (with editorial adaptations) from materials provided by Helmholtz Association of German Research Centres.

Journal Reference:

Mingchun Xu, Youkun Gao, Elias Moreno, Marinus Kunst, Martin Muhler, Yuemin Wang, Hicham Idriss, Christof Wöll. Photocatalytic Activity of Bulk TiO_{2} Anatase and Rutile Single Crystals Using Infrared Absorption Spectroscopy. Physical Review Letters, 2011; 106 (13) DOI: 10.1103/PhysRevLett.106.138302

Lights and flat-panel displays: Researchers 'brighten' the future of organic light-emitting diode technology

 Chlorine is an abundant and readily available halogen gas commonly associated with the sanitation of swimming pools and drinking water. Could a one-atom thick sheet of this element revolutionize the next generation of flat-panel displays and lighting technology?

In the case of Organic Light-Emitting Diode (OLED) devices, it most certainly can. Primary researchers Michael G. Helander (PhD Candidate and Vanier Canada Graduate Scholar), Zhibin Wang (PhD Candidate), and led by Professor Zheng-Hong Lu of the Department of Materials Science & Engineering at the University of Toronto, have found a simple method of using chlorine to drastically reduce traditional OLED device complexity and dramatically improve its efficiency all at the same time. By engineering a one-atom thick sheet of chlorine onto the surface of an existing industry-standard electrode material (indium tin oxide, ITO) found in today's flat-panel displays, these researchers have created a medium that allows for efficient electrical transport while eliminating the need for several costly layers found in traditional OLED devices.

"It turns out that it's remarkably easy to engineer this one-atom thick layer of chlorine onto the surface of ITO," says Helander. "We developed a UV light assisted process to achieve chlorination, which negates the need for chlorine gas, making the entire procedure safe and reliable."

The team tested their green-emitting "Cl-OLED" against a conventional OLED and found that the efficiency was more than doubled at very high brightness. "OLEDs are known for their high-efficiency," says Helander. "However, the challenge in conventional OLEDs is that as you increase the brightness, the efficiency drops off rapidly."

Using their chlorinated ITO, this team of advanced materials researchers found that they were able to prevent this drop off and achieve a record efficiency of 50% at 10,000 cd/m2 (a standard florescent light has a brightness of approximately 8,000 cd/m2), which is at least two times more efficient than the conventional OLED.

"Our Cl-ITO eliminates the need for several stacked layers found in traditional OLEDs, reducing the number of manufacturing steps and equipment, which ultimately cuts down on the costs associated with setting up a production line," says Professor Zheng-Hong Lu.

"This effectively lowers barriers for mass production and thereby accelerates the adoption of OLED devices into mainstream flat-panel displays and other lighting technologies."

The results of this work are published online in the journal Science on April 14, 2011.

Story Source:

The above story is reprinted (with editorial adaptations) from materials provided by University of Toronto Faculty of Applied Science and Engineering.

Journal Reference:

M. G. Helander, Z. B. Wang, J. Qiu, M. T. Greiner, D. P. Puzzo, Z. W. Liu, and Z. H. Lu. Chlorinated Indium Tin Oxide Electrodes with High Work Function for Organic Device Compatibility. Science, 14 April 2011 DOI: 10.1126/science.1202992