Spallation Neutron Source puts the squeeze on methane hydrate cages

Our robot would find this energy source in shale deposits, notably here on the east coast of the United States. However, the most abundant deposits of natural gas are under water on the continental shelves and in the permafrost in the Arctic region. At both poles, methane mixes with water and freezes, remaining trapped as an ice-like compound, for millions of years.

Much further afield, methane, along with water and ammonia, are major constituents of Saturn's icy moon Titan. Some scientists speculate that on Titan there is a methanological cycle similar to the hydrological cycle here on earth. Surface methane evaporates into the atmosphere, where it condenses, and rains down to the surface again. NASA's Cassini-Huygens Titan probe has been there and sampled it.

Methane holds promise as an abundant energy source for tomorrow, but it is Janus-faced: While often referred to as the cleanest fossil fuel producing far less greenhouse gas than either coal or oil, historically it has been seen as a major source of environmental pollution. That's because burning it produces carbon dioxide, a very potent greenhouse gas.

Scientists are looking at how to sequester that CO2 byproduct, in an ice-like state. Such a strategy would create a carbon 'energy cycle' in which the methane resource is recovered, used, and then the greenhouse gas sequestered in a form very closely related to the naturally occuring initial materials.

"What we do know right now is that when methane is taken up and released into the environment, water plays a critical role", said Chris Tulk, lead instrument scientist on the Spallation Neutrons and Pressure Diffractometer (SNAP) at ORNL. "Whether it is in the oceans where hydrates form on continental shelves, in the icy permafrost conditions, or even as these materials decompose and release the methane into the atmosphere to contribute to the greenhouse effect, water is certainly involved in the process. This research should lead to better models of how hydrocarbons are taken up and released in the environment."

To develop such models, they need to understand at the molecular level the relationship between methane and water. Researchers have discovered that water forms cages, called clathrates, that contain "guest" molecules of methane and of many of the Noble gases.

At SNAP, a combination of a state-of-the-art instrument, clever experimental technique, and excellent samples have for the first time yielded detailed data on the structure of these methane hydrate clathrates.

Under pressure of more than 600,000 pounds per square inch, they found that the correct occupancy for the largest cages in this beautiful structure is three methane molecules. This finding can now be used to benchmark methane and water interactions at various energy and pressure, and researchers can better characterize the hydrophobic interaction.

"We've done a lot of work on these clathrate compounds," said Tulk, "but this is the first work in which all the work could be done on SNAP.

"When we compress the methane clathrate hydrate, it goes through a phase change at the molecular level to a new high pressure form known as structure H, for the hexagonal (six-sided) arrangement of water," Tulk explained.

"As the pressure is increased and the sample becomes smaller, the overall density increases, as expected. But the water molecules re-arrange themselves to form larger cages. These larger cages can now accommodate more than one methane molecule. The key question in this research was, how many methane molecules are in these larger cages, and how are they arranged?"

The SNAP instrument is perfectly suited to provide these types of structural details. "The repulsive interaction between methane and water, called the hydrophobic interaction, is poorly understood," Tulk explained. "And the interaction between methane and methane, particularly when the molecules are nearly in contact and strongly repelling, is not well understood at all."

Understanding how many methanes are able to fit in each cage and how the methane molecules are arranged within these cages, provides insight into these interactions.

The research also assists computational simulation. There are currently no good models to predict clathrate structure. "Determining how many methane molecules are in a cage will give the computational chemistry folks something to shoot for with their hydrate models," Tulk said.

Given these experimental results to come up with a new "potential" -- i.e., a new calculation of the interaction force that exists between methane molecules, and between methane and water - computational chemists can calculate the way methane interacts with water in the larger environment.

The ball is now in the hands of the theorists, who must come up with a model that correctly predicts this experimental observation. Then they can extend the model to better predict how water and hydrocarbons interact in the larger environment.

"That is the driving motivation for my research, to get a fundamental physics-chemistry perspective on these things that have such a large impact on the earth."

Provided by Oak Ridge National Laboratory (news : web)

Neutron scattering provides window into surface interactions

To better understand the fundamental behavior of molecules at surfaces, researchers at the U.S. Department of Energy's Oak Ridge National Laboratory are combining the powers of neutron scattering with chemical analysis.

Scientists have a fundamental interest in how molecules behave at solid surfaces because surface interactions influence chemistry, such as in materials for catalysis, drug delivery and carbon sequestration. Understanding these interactions allows researchers to tailor materials for a specific desirable outcome.

Michelle Kidder and A.C. Buchanan, physical organic chemists, and Ken Herwig, neutron scattering scientist, used neutron scattering to study the physical motion of a chemically attached organic molecule inside a silica nanopore, MCM41.

"There is a connection between a molecule's dynamic behavior or motion to its surroundings." Herwig said. "In particular, restricting the ability of a molecule to freely move by confining it to a small volume dramatically affects both the range and character of its movement. We are trying to gain insight into the connection between the changes in molecular motion and the changes in chemistry that occur when molecules are attached to a solid surface."

Herwig used neutron scattering to gain a unique perspective into molecular motion because neutrons are sensitive to the hydrogen atoms, which are present in many molecules that researchers are interested in. Additionally, neutron scattering simultaneously tells researchers how rapid the motion is and what type of motion they are observing on the atomic and nanoscale.

If scientists understand how pore size affects surface interactions, they can modify pore size to change a chemical product outcome.

To study surface interactions, Kidder synthesized both the organic molecules and MCM41 of different pore sizes, then chemically attached the molecules to the silica pore surface, which forms an organic-inorganic hybrid material. This hybrid material is used in studies to understand chemical decomposition pathways, where surface interactions were presumed to play a role.

"We are interested in understanding the thermo decomposition of molecules similar to those found in biomass resources," Kidder said. "What we have seen is that there are many local environmental factors that influence chemical reactivity and products, and one of those large influences occurs when a molecule is confined to a pore wall, where even the pore size has a large impact on reactivity."

This research was funded by DOE's Office of Science.

Story Source:

The above story is reprinted from materials provided by DOE/Oak Ridge National Laboratory.

Note: Materials may be edited for content and length. For further information, please contact the source cited above.

Journal Reference:

Edward J. Kintzel, Michelle K. Kidder, A. C. Buchanan, Phillip F. Britt, Eugene Mamontov, Michaela Zamponi, Kenneth W. Herwig. Dynamics of 1,3-Diphenylpropane Tethered to the Interior Pore Surfaces of MCM-41. The Journal of Physical Chemistry C, 2012; 116 (1): 923 DOI: 10.1021/jp209458a

'Low tech' light in neutron beam illuminates photosynthesis in bacteria

Researchers at the Bio-SANS instrument at the High Flux Isotope Reactor are getting a leg up in their research from an ingenious "low tech" lighting tool that can be fixed to their samples and then pushed directly into the neutron beam, to illuminate the response of layers of cyanobacteria to changes in light.

"It's really low tech," says Volker Urban, lead instrument scientist on the Bio-SANS, with a grin. "You can buy the parts anywhere." The lighting tool is the work of graduate student Brad O'Dell, a visiting intern from Cambridge University in the United Kingdom. The device combines light emitting diodes with the electronics that drive the illumination.

Parts off the shelf it may be, but the device facilitates research into biologically inspired solar cell devices, important alternative energy-related research being conducted with funding from the Photosynthetic Antenna Research Center one of the Energy Frontier Research Centers in the US.

Photosynthesis is the process by which plants convert sunlight into energy. Bacteria, algae and plants have natural sensors called light-harvesting antenna systems that capture the sun's light and transfer the energy to reaction centers, where the electron transfer for photochemistry occurs. Such antenna complexes are highly specialized in nature, allowing organisms to capture the maximum light energy available in their environment.

Researchers at the Bio-SANS are now using the new LED lighting tool to study the light response of the membrane stacks in cyanobacteria, a blue-green algae found in almost every environment, from oceans to fresh water to bare rock to soil.

At the Bio-SANS, the bacteria are loaded into cuvettes, small sample holders that resemble tiny transparent banjos. An LED is fixed to the top of each cuvette. The array is then pushed into the sample holder and the neutron beam passes through a window, taking "pictures" of the response of the layers of the bacteria to variations in light from the attached LEDs.

"We push the samples into the neutron beam - and then from the neutron scattering we can observe how the structure changes, depending on how much light of which color we shine on the samples," Urban said. "Ultimately, we want to find out how nature has solved the problem of optimizing the efficient use of solar energy through these intricate architectures of antennas. These collect sunlight and funnel the light energy to reaction centers, where it is converted into chemical energy that can be stored for further use," he said. "If those fundamental principles are better understood then they can be used to create new, more efficient solar panels." They have already made some observations. "In a preliminary experiment, we could see with neutrons that the membrane stacking in the cycnobacteria changes in response to light on/ light off," Urban said. "With this new light in place, we can now study this response more precisely, and in more detail: How does it depend on the intensity and the color of the light?"

In related recent work, also funded by PARC, Urban and his collaborators performed small-angle neutron scattering studies to obtain structural information about the photosynthetic apparatus of the light-harvesting chlorosome complex, the light-harvesting B808-866 complex, and the bacterium Chloroflexus aurantiacus. "To our knowledge, this was the first SANS report regarding the overall photosynthetic machinery of Cfx. Aurantiacus," Urban said.

Subsequently, the researchers studied in greater detail the light harvesting antenna chlorosome. Chlorosomes, from green photosynthetic bacteria, are the largest and one of the most efficient light-harvesting antenna complexes found in nature. The chlorosome is able to absorb solar energy and convert it into chemical energy under both low and high light conditions. Its unique properties make it an attractive candidate for developing biohybrid solar cell devices.

The paper that resulted was the first to investigate the ionic strength effects of chlorosomes, whose size, shape, and orientation of the light-harvesting complexes are critical to understand for the phenomenon of electron transfer to semiconductor electrodes in solar devices.

"These studies are useful for developing biomimetic and bioanalytical solar cell devices, and for demonstrating that chlorosomes are alternatives to other protein_pigment complexes produced in photosynthetic organisms," Urban said.

Provided by Oak Ridge National Laboratory (news : web)

Neutron analysis reveals unique atom-scale behavior of 'cobalt blue'

 Neutron scattering studies of "cobalt blue," a compound prized by artists for its lustrous blue hue, are revealing unique magnetic characteristics that could answer questions about mysterious properties in other materials.

Experiments at the Spallation Neutron Source (SNS) and High Flux Isotope Reactor (HFIR), both located at the Department of Energy's Oak Ridge National Laboratory, indicate novel behaviors in the antiferromagnetic material cobalt aluminum oxide, -- CoAl2O4, or cobalt aluminate -- which researcher Gregory MacDougall of ORNL's Neutron Scattering Sciences Division describes as a "highly frustrated magnetic system."

"Frustrated" in this context refers to a condition where competing interactions between the magnetic spins within the atomic structure prevent the establishment of a long-range ordered state.

"Frustration is often associated with exotic behavior in materials, including piezoelectricity, multiferrocity, and high-temperature superconductivity, each of which is potentially important for future energy-efficient technologies," MacDougall said.

Antiferromagnetism is a type of magnetic order commonly found in materials below a certain temperature where the microscopic magnetic moments (often called "spins") on neighboring atoms align with their north and south poles oriented in opposite directions. Long-range antiferromagnetic order is technologically important for magnetic information storage.

The single-crystal experiments performed at ORNL showed the magnetic properties of cobalt aluminate exhibited drastic changes at the numbingly low temperature of 6.5 Kelvin. The experiments showed that effects from competing interactions may be responsible for its intriguing but poorly understood magnetic properties.

"Cobalt blue demonstrates behaviors that have never before been appreciated in a frustrated magnet, but have been seen in other materials," MacDougall said.

"Typically, frustration in the lattice from different energy scales and competing interactions drives the ordering temperature down. What we've found is, instead of eliminating ordering entirely, the long-range order is broken up into several small domains, in which the motion of the domain walls is frozen into place," MacDougall said.

Sharp walls separate those smaller atom-scale domains, set apart by the orientation of the atoms' magnetic spin. The result of freezing such walls into place is a glass-like behavior, normally indicative of highly disordered structure.

In cobalt aluminate's case, however, the glass-like behavior is exhibited on a very clean, ordered crystal. "We think this may explain unexpected glass-like behavior in other frustrated systems," MacDougall said.

The research, reported in Proceedings of the National Academy of Sciences, is part of a larger program to study magnetic frustration -- what happens in magnetic systems when the geometry of the system or competing interactions frustrate or suppress the interactions that normally drive order, allowing novel behaviors to emerge.

"This is where you discover new physics," MacDougall said.

Cobalt aluminate is the compound responsible for cobalt blue, a vivid pigment used in paintings, colored glass and even to color concrete.

"In the past seven or eight years people have become interested in cobalt blue's magnetic properties because it turns out to be a prototypical system where competing interactions suppress magnetic order, and it is predicted to have novel ground states," MacDougall said.

The experiments were performed on two of HFIR's Triple Axis Spectrometers and the SNS's Cold Chopper Neutron Spectrometer (CNCS), making use of both thermal and "chilled," low-energy neutrons to study the cobalt aluminate at low, near absolute-zero temperatures. The single-crystal samples were fabricated in collaboration with ORNL's Correlated Electron Materials group.

MacDougall and colleagues used the triple-axis spectrometers at HFIR to study the ordering pattern of the cobalt blue lattice, which revealed the smaller domains forming at low temperatures. With SNS's CNCS, the researchers were able to study how long-lengthscale perturbations in the magnetic ordered states, known as "spin-waves," moved through the system. The speed of those spin waves in different directions is a sensitive measure of the strength of the interactions between atoms in the cobalt blue system.

Story Source:

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

Journal Reference:

Gregory J. MacDougall, Delphine Gout, Jerel L. Zarestky, Georg Ehlers, Andrey Podlesnyak, Michael A. McGuire, David Mandrus, Stephen E. Nagler. Kinetically inhibited order in a diamond-lattice antiferromagnet. Proceedings of the National Academy of Sciences, 2011; DOI: 10.1073/pnas.1107861108

Neutron analysis yields insight into bacteria for solar energy

Structural studies of some of nature's most efficient light-harvesting systems are lighting the way for new generations of biologically inspired solar cell devices.

Researchers from Washington University in St. Louis and the Department of Energy's Oak Ridge National Laboratory used small-angle neutron scattering to analyze the structure of chlorosomes in green photosynthetic bacteria. Chlorosomes are efficient at collecting sunlight for conversion to energy, even in low-light and extreme environments.

"It's one of the most efficient light harvesting antenna complexes found in nature," said co-author and research scientist Volker Urban of ORNL's Center for Structural Molecular Biology, or CSMB.

Neutron analysis performed at the CSMB's Bio-SANS instrument at the High Flux Isotope Reactor allowed the team to examine chlorosome structure under a range of thermal and ionic conditions.

"We found that their structure changed very little under all these conditions, which shows them to be very stable," Urban said. "This is important for potential biohybrid applications -- if you wanted to use them to harvest light in synthetic materials like a hybrid solar cell, for example."

The size, shape and organization of light-harvesting complexes such as chlorosomes are critical factors in electron transfer to semiconductor electrodes in solar devices. Understanding how chlorosomes function in nature could help scientists mimic the chlorosome's efficiency to create robust biohybrid or bio-inspired solar cells.

"What's so amazing about the chlorosome is that this large and complicated assembly is able to capture light effectively across a large area and then funnel the light to the reaction center without losing it along the way," Urban said. "Why this works so well in chlorosomes is not well understood at all."

"We're trying to find out general principles that are important for capturing, harvesting and transporting light efficiently and see how nature has solved that," Urban said.

Small-angle neutron scattering enabled the team to clearly observe the complicated biological systems at a nanoscale level without damaging the samples.

"With neutrons, you have an advantage that you get a very sharp contrast between these two phases, the chlorosome and the deuterated buffer. This gives you something like a clear black and white image," Urban said.

The team, led by Robert Blankenship of Washington University, published its findings in the journal Langmuir. The research was supported through the Photosynthetic Antenna Research Center, an Energy Frontier Research Center funded by DOE's Office of Science. Both HFIR and the Bio-SANS facility at ORNL's Center for Structural Molecular Biology are also supported by DOE's Office of Science.

ORNL is managed by UT-Battelle for the Department of Energy's Office of Science.

Story Source:

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

Journal Reference:

Kuo-Hsiang Tang, Liying Zhu, Volker S. Urban, Aaron M. Collins, Pratim Biswas, Robert E. Blankenship. Temperature and Ionic Strength Effects on the Chlorosome Light-Harvesting Antenna Complex. Langmuir, 2011; 110315121146005 DOI: 10.1021/la104532b

'Tall order' sunlight-to-hydrogen system works, neutron analysis confirms

 Researchers at the Department of Energy's Oak Ridge National Laboratory have developed a biohybrid photoconversion system -- based on the interaction of photosynthetic plant proteins with synthetic polymers -- that can convert visible light into hydrogen fuel.

Photosynthesis, the natural process carried out by plants, algae and some bacterial species, converts sunlight energy into chemical energy and sustains much of the life on earth. Researchers have long sought inspiration from photosynthesis to develop new materials to harness the sun's energy for electricity and fuel production.

In a step toward synthetic solar conversion systems, the ORNL researchers have demonstrated and confirmed with small-angle neutron scattering analysis that light harvesting complex II (LHC-II) proteins can self-assemble with polymers into a synthetic membrane structure and produce hydrogen.

The researchers envision energy-producing photoconversion systems similar to photovoltaic cells that generate hydrogen fuel, comparable to the way plants and other photosynthetic organisms convert light to energy.

"Making a, self-repairing synthetic photoconversion system is a pretty tall order. The ability to control structure and order in these materials for self-repair is of interest because, as the system degrades, it loses its effectiveness," ORNL researcher Hugh O'Neill, of the lab's Center for Structural Molecular Biology, said.

"This is the first example of a protein altering the phase behavior of a synthetic polymer that we have found in the literature. This finding could be exploited for the introduction of self-repair mechanisms in future solar conversion systems," he said.

Small angle neutron scattering analysis performed at ORNL's High Flux Isotope Reactor (HFIR) showed that the LHC-II, when introduced into a liquid environment that contained polymers, interacted with polymers to form lamellar sheets similar to those found in natural photosynthetic membranes.

The ability of LHC-II to force the assembly of structural polymers into an ordered, layered state -- instead of languishing in an ineffectual mush -- could make possible the development of biohybrid photoconversion systems. These systems would consist of high surface area, light-collecting panes that use the proteins combined with a catalyst such as platinum to convert the sunlight into hydrogen, which could be used for fuel.

The research builds on previous ORNL investigations into the energy-conversion capabilities of platinized photosystem I complexes -- and how synthetic systems based on plant biochemistry can become part of the solution to the global energy challenge.

"We're building on the photosynthesis research to explore the development of self-assembly in biohybrid systems. The neutron studies give us direct evidence that this is occurring," O'Neill said.

The researchers confirmed the proteins' structural behavior through analysis with HFIR's Bio-SANS, a small-angle neutron scattering instrument specifically designed for analysis of biomolecular materials.

"Cold source" neutrons, in which energy is removed by passing them through cryogenically chilled hydrogen, are ideal for studying the molecular structures of biological tissue and polymers.

The LHC-II protein for the experiment was derived from a simple source: spinach procured from a local produce section, then processed to separate the LHC-II proteins from other cellular components. Eventually, the protein could be synthetically produced and optimized to respond to light.

O'Neill said the primary role of the LHC-II protein is as a solar collector, absorbing sunlight and transferring it to the photosynthetic reaction centers, maximizing their output. "However, this study shows that LHC-II can also carry out electron transfer reactions, a role not known to occur in vivo," he said.

The research team, which came from various laboratory organizations including its Chemical Sciences Division, Neutron Scattering Sciences Division, the Center for Structural Molecular Biology and the Center for Nanophase Materials Sciences, consisted of O'Neill, William T. Heller, and Kunlun Hong, all of ORNL; Dimitry Smolensky of the University of Tennessee; and Mateus Cardoso, a former postdoctoral researcher at ORNL now of the Laboratio Nacional de Luz Sincrotron in Brazil.

"That's one of the nice things about working at a national laboratory. Expertise is available from a variety of organizations," O'Neill said.

The work, published in the journal Energy & Environmental Science, was supported with Laboratory-Directed Research and Development funding. HFIR is supported by the DOE Office of Science.

Story Source:

The above story is reprinted (with editorial adaptations by ScienceDaily staff) from materials provided by DOE/Oak Ridge National Laboratory.

Journal Reference:

Mateus B. Cardoso, Dmitriy Smolensky, William T. Heller, Kunlun Hong, Hugh O'Neill. Supramolecular assembly of biohybrid photoconversion systems. Energy & Environmental Science, 2011; 4 (1): 181 DOI: 10.1039/C0EE00369G

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