Wednesday, March 14, 2012

Catalysts for less: Slashing costs of metal alloys needed to jump-start crucial chemical processes

 When you hear the word hydrogenation, you might think of Crisco or margarine -- plant oils made thicker and more stable by adding hydrogen atoms. In fact, hydrogenation is a key process in a large number of industries, such as oil refining, where it is used to turn crude oil into gasoline.

Hydrogenation happens thanks to the presence of a catalyst -- usually a metal, such as nickel or palladium, or an alloy -- which allows the hydrogen atoms to bind with other molecules. Typically, metal alloys are mixtures of cheap common metals, such as nickel, and expensive precious metals, such as platinum or palladium. However, it is hard to produce alloys that are selective hydrogenation catalysts, which are able to attach the hydrogen atoms to specific sites on a molecule.

Now scientists at Tufts have found a way to create a selective hydrogenation catalyst by scattering single atoms of palladium onto a copper base. This catalyst requires less of the expensive metal, and the process is greener, too, offering potentially significant economic and environmental benefits.

The team reported its discovery in a paper published on March 9 in the journal Science.

Led by Charles Sykes, an associate professor of chemistry in the School of Arts and Sciences, the group of researchers heated up very small amounts of palladium to almost 1,000 degrees Celsius, or about 1,830 degrees Fahrenheit. At that temperature, the metal evaporated like a gas, so that single atoms were released. These atoms, less than half a nanometer wide, embedded themselves into a copper metal surface about three inches away.

Using a scanning tunneling microscope, which can capture pictures of objects at the atomic level, the researchers verified that single palladium atoms had indeed embedded themselves at scattered intervals in the copper. In a conventional metal catalyst, by contrast, palladium is used in clumps 5 to 10 nanometers wide. This is significantly less economical, since it requires much greater quantities of palladium, which costs more than $650 an ounce. It is less environmentally friendly as well, because of the energy that must be used to extract the additional necessary palladium from raw ore.

The new catalyst also behaves differently, says Georgios Kyriakou, a research assistant professor in chemistry and first author of the report. He helped determine that the single atom alloy was more effective in catalyzing hydrogenation than denser mixtures of palladium and copper.

"In the face of precious metals scarcity and exorbitant prices, these systems are promising in the search for sustainable global solutions," says Maria Flytzani-Stephanopoulos, the Robert and Marcy Haber Endowed Professor in Energy Sustainability in the School of Engineering, whose lab is studying the effectiveness of the single-atom process. She and Sykes are continuing to collaborate on advancing their research, funded by the National Science Foundation, the U.S. Department of Energy and Tufts Collaborates, a grant program administered by the Office of the Provost.

Flytzani-Stephanopoulos and her group in the School of Engineering are now looking into other approaches to achieve hydrogenation with different metal pairs. She says that eventually single-atom alloy catalysts could be used as low-cost alternatives for hydrogenation and dehydrogenation. That could be a boon for the production of agricultural chemicals, foods and pharmaceuticals.

Story Source:

The above story is reprinted from materials provided by Tufts University. The original article was written by Taylor McNeil.

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

Journal Reference:

G. Kyriakou, M. B. Boucher, A. D. Jewell, E. A. Lewis, T. J. Lawton, A. E. Baber, H. L. Tierney, M. Flytzani-Stephanopoulos, E. C. H. Sykes. Isolated Metal Atom Geometries as a Strategy for Selective Heterogeneous Hydrogenations. Science, 2012; 335 (6073): 1209 DOI: 10.1126/Science.1215864

Nanotube technology leading to new era of fast, lower-cost medical diagnostics

 Researchers at Oregon State University have tapped into the extraordinary power of carbon "nanotubes" to increase the speed of biological sensors, a technology that might one day allow a doctor to routinely perform lab tests in minutes, speeding diagnosis and treatment while reducing costs.

The new findings have almost tripled the speed of prototype nano-biosensors, and should find applications not only in medicine but in toxicology, environmental monitoring, new drug development and other fields.

The research was just reported in Lab on a Chip, a professional journal. More refinements are necessary before the systems are ready for commercial production, scientists say, but they hold great potential.

"With these types of sensors, it should be possible to do many medical lab tests in minutes, allowing the doctor to make a diagnosis during a single office visit," said Ethan Minot, an OSU assistant professor of physics. "Many existing tests take days, cost quite a bit and require trained laboratory technicians.

"This approach should accomplish the same thing with a hand-held sensor, and might cut the cost of an existing $50 lab test to about $1," he said.

The key to the new technology, the researchers say, is the unusual capability of carbon nanotubes. An outgrowth of nanotechnology, which deals with extraordinarily small particles near the molecular level, these nanotubes are long, hollow structures that have unique mechanical, optical and electronic properties, and are finding many applications.

In this case, carbon nanotubes can be used to detect a protein on the surface of a sensor. The nanotubes change their electrical resistance when a protein lands on them, and the extent of this change can be measured to determine the presence of a particular protein -- such as serum and ductal protein biomarkers that may be indicators of breast cancer.

The newest advance was the creation of a way to keep proteins from sticking to other surfaces, like fluid sticking to the wall of a pipe. By finding a way to essentially "grease the pipe," OSU researchers were able to speed the sensing process by 2.5 times.

Further work is needed to improve the selective binding of proteins, the scientists said, before it is ready to develop into commercial biosensors.

"Electronic detection of blood-borne biomarker proteins offers the exciting possibility of point-of-care medical diagnostics," the researchers wrote in their study. "Ideally such electronic biosensor devices would be low-cost and would quantify multiple biomarkers within a few minutes."

This work was a collaboration of researchers in the OSU Department of Physics, Department of Chemistry, and the University of California at Santa Barbara. A co-author was Vincent Remcho, professor and interim dean of the OSU College of Science, and a national expert in new biosensing technology.

The research was supported by the U.S. Army Research Laboratory through the Oregon Nanoscience and Microtechnologies Institute.

Story Source:

The above story is reprinted from materials provided by Oregon State University.

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

Journal Reference:

Matthew R. Leyden, Robert J. Messinger, Canan Schuman, Tal Sharf, Vincent T. Remcho, Todd M. Squires, Ethan D. Minot. Increasing the detection speed of an all-electronic real-time biosensor. Lab on a Chip, 2012; 12 (5): 954 DOI: 10.1039/C2LC21020G

Metamaterials may advance with new femtosecond laser technique

Researchers in applied physics have cleared an important hurdle in the development of advanced materials, called metamaterials, that bend light in unusual ways.

Working at a scale applicable to infrared light, the Harvard team has used extremely short and powerful laser pulses to create three-dimensional patterns of tiny silver dots within a material. Those suspended metal dots are essential for building futuristic devices like invisibility cloaks.

The new fabrication process, described in the journal Applied Physics Letters, advances nanoscale metal lithography into three dimensions -- and does it at a resolution high enough to be practical for metamaterials.

"If you want a bulk metamaterial for visible and infrared light, you need to embed particles of silver or gold inside a dielectric, and you need to do it in 3D, with high resolution," says lead author Kevin Vora, a graduate student at the Harvard School of Engineering and Applied Sciences (SEAS).

"This work demonstrates that we can create silver dots that are disconnected in x, y, and z," Vora says. "There's no other technique that feasibly allows you to do that. Being able to make patterns of nanostructures in 3D is a very big step towards the goal of making bulk metamaterials."

Vora works in the laboratory of Eric Mazur, Balkanski Professor of Physics and Applied Physics at SEAS. For decades, Mazur has been using a piece of equipment called a femtosecond laser to investigate how very tightly focused, powerful bursts of light can change the electrical, optical, and physical properties of a material.

When a conventional laser shines on a transparent material, the light passes straight through, with slight refraction. The femtosecond laser is special because it emits a burst of photons as bright as the surface of the sun in a flash lasting only 50 quadrillionths (5 × 10-14) of a second. Instead of shining through the material, that energy gets trapped within it, exciting the electrons within the material and achieving a phenomenon known as nonlinear absorption.

Inside the pocket where that energy is trapped, a chemical reaction can take place, permanently altering the internal structure of the material. The process has previously been exploited for 2D and simple 3D metal nanofabrication.

"Normally, when people use femtosecond lasers in fabrication, they're creating a wood pile structure: something stacked on something else, being supported by something else," explains Mazur.

"If you want to make an array of silver dots, however, they can't float in space."

In the new process, Vora, Mazur, and their colleagues combine silver nitrate, water, and a polymer called PVP into a solution, which they bake onto a glass slide. The solid polymer then contains ions of silver, which are photoreduced by the tightly focused laser pulses to form nanocrystals of silver metal, supported by the polymer matrix.

The need for this particular combination of chemicals, at the right concentrations, was not obvious in prior work. Researchers sometimes combine silver nitrate with water in order to create silver nanostructures, but that process provides no structural support for a 3D pattern. Another process combines silver nitrate, water, PVP, and ethanol, but the samples darken and degrade very quickly by producing silver crystals throughout the polymer.

With ethanol, the reaction happens too quickly and uncontrollably. Mazur's team needed nanoscale crystals, precisely distributed and isolated in 3D.

"It was just a question of removing that reagent, and we got lucky," Vora says. "What was most surprising about it was how simple it is. It was a matter of using less."

SeungYeon Kang, a graduate student at SEAS, and Shobha Shukla, a former postdoctoral fellow, coauthored the paper. The work was supported by the Air Force Office of Scientific Research.

Story Source:

The above story is reprinted from materials provided by Harvard School of Engineering and Applied Sciences, via AlphaGalileo.

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

Journal Reference:

Kevin Vora, SeungYeon Kang, Shobha Shukla, Eric Mazur. Fabrication of disconnected three-dimensional silver nanostructures in a polymer matrix. Applied Physics Letters, 2012; 100 (6): 063120 DOI: 10.1063/1.3684277

Touch of gold improves nanoparticle fuel-cell reactions

 Chemists at Brown University have created a triple-headed metallic nanoparticle that reportedly performs better and lasts longer than any other nanoparticle catalyst studied in fuel-cell reactions. The key is the addition of gold: It yields a more uniform crystal structure while removing carbon monoxide from the reaction.

Results are published in the Journal of the American Chemical Society.

Advances in fuel-cell technology have been stymied by the inadequacy of metals studied as catalysts. The drawback to platinum, other than cost, is that it absorbs carbon monoxide in reactions involving fuel cells powered by organic materials like formic acid. A more recently tested metal, palladium, breaks down over time.

Now chemists at Brown University have created a triple-headed metallic nanoparticle that they say outperforms and outlasts all others at the anode end in formic-acid fuel-cell reactions. In a paper published in the Journal of the American Chemical Society, the researchers report a 4-nanometer iron-platinum-gold nanoparticle (FePtAu), with a tetragonal crystal structure, generates higher current per unit of mass than any other nanoparticle catalyst tested. Moreover, the trimetallic nanoparticle at Brown performs nearly as well after 13 hours as it did at the start. By contrast, another nanoparticle assembly tested under identical conditions lost nearly 90 percent of its performance in just one-quarter of the time.

"We've developed a formic acid fuel-cell catalyst that is the best to have been created and tested so far," said Shouheng Sun, chemistry professor at Brown and corresponding author on the paper. "It has good durability as well as good activity."

Gold plays key roles in the reaction. First, it acts as a community organizer of sorts, leading the iron and platinum atoms into neat, uniform layers within the nanoparticle. The gold atoms then exit the stage, binding to the outer surface of the nanoparticle assembly. Gold is effective at ordering the iron and platinum atoms because the gold atoms create extra space within the nanoparticle sphere at the outset. When the gold atoms diffuse from the space upon heating, they create more room for the iron and platinum atoms to assemble themselves. Gold creates the crystallization chemists want in the nanoparticle assembly at lower temperature.

Gold also removes carbon monoxide (CO) from the reaction by catalyzing its oxidation. Carbon monoxide, other than being dangerous to breathe, binds well to iron and platinum atoms, gumming up the reaction. By essentially scrubbing it from the reaction, gold improves the performance of the iron-platinum catalyst. The team decided to try gold after reading in the literature that gold nanoparticles were effective at oxidizing carbon monoxide -- so effective, in fact, that gold nanoparticles had been incorporated into the helmets of Japanese firefighters. Indeed, the Brown team's triple-headed metallic nanoparticles worked just as well at removing CO in the oxidation of formic acid, although it is unclear specifically why.

The authors also highlight the importance of creating an ordered crystal structure for the nanoparticle catalyst. Gold helps researchers get a crystal structure called "face-centered-tetragonal," a four-sided shape in which iron and platinum atoms essentially are forced to occupy specific positions in the structure, creating more order. By imposing atomic order, the iron and platinum layers bind more tightly in the structure, thus making the assembly more stable and durable, essential to better-performing and longer-lasting catalysts.

In experiments, the FePtAu catalyst reached 2809.9 mA/mg Pt (mass-activity, or current generated per milligram of platinum), "which is the highest among all NP (nanoparticle) catalysts ever reported," the Brown researchers write. After 13 hours, the FePtAu nanoparticle has a mass activity of 2600mA/mg Pt, or 93 percent of its original performance value. In comparison, the scientists write, the well-received platinum-bismuth nanoparticle has a mass activity of about 1720mA/mg Pt under identical experiments, and is four times less active when measured for durability.

The researchers note that other metals may be substituted for gold in the nanoparticle catalyst to improve the catalyst's performance and durability.

"This communication presents a new structure-control strategy to tune and optimize nanoparticle catalysis for fuel oxidations," the researchers write.

Sen Zhang, a third-year graduate student in Sun's lab, helped with the nanoparticle design and synthesis. Shaojun Guo, a postdoctoral fellow in Sun's lab performed electrochemical oxidation experiments. Huiyuan Zhu, a second-year graduate student in Sun's lab, synthesized the FePt nanoparticles and ran control experiments. The other contributing author is Dong Su from the Center for Functional Nanomaterials at Brookhaven National Laboratory, who analyzed the structure of the nanoparticle catalyst using the advanced electron microscopy facilities there.

The U.S. Department of Energy and the Exxon Mobil Corporation funded the research.

Story Source:

The above story is reprinted from materials provided by Brown University.

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

Journal Reference:

Sen Zhang, Shaojun Guo, Huiyuan Zhu, Dong Su, Shouheng Sun. Structure-Induced Enhancement in Electrooxidation of Trimetallic FePtAu Nanoparticles. Journal of the American Chemical Society, 2012; 120309140246002 DOI: 10.1021/ja300708j

Nanofiber breakthrough holds promise for medicine and microprocessors

 A new method for creating nanofibers made of proteins, developed by researchers at Polytechnic Institute of New York University (NYU-Poly), promises to greatly improve drug delivery methods for the treatment of cancers, heart disorders and Alzheimer's disease, as well as aid in the regeneration of human tissue, bone and cartilage.

In addition, applied differently, this same development could point the way to even tinier and more powerful microprocessors for future generations of computers and consumer electronics devices.

The details are spelled out in an article titled "Effects of Divalent Metals on Nanoscopic Fiber Formation and Small Molecule Recognition of Helical Proteins," which appears online in Advanced Functional Materials. Author Susheel K. Gunasekar, a doctoral student in NYU-Poly's Department of Chemical and Biological Sciences, was the primary researcher, and is a student of co-author Jin Montclare, assistant professor and head of the department's Protein Engineering and Molecular Design Lab, where the underlying research was primarily conducted. Also involved were co-authors Luona Anjia, a graduate student, and Professor Hiroshi Matsui, both of the Department of Chemistry and Biochemistry at Hunter College (The City University of New York), where secondary research was conducted.

Yet all of this almost never emerged, says Professor Montclare, who explains that it was sheer "serendipity" -- a chance observation made by Gunasekar two years ago -- that inspired the team's research and led to its significant findings.

During an experiment that involved studying certain cylinder-shaped proteins derived from cartilage oligomeric matrix protein (COMP, found predominantly in human cartilage), Gunasekar noticed that in high concentrations, these alpha helical coiled-coil proteins spontaneously came together and self-assembled into nanofibers. It was a surprising outcome, Montclare says, because COMP was not known to form fibers at all. "We were really excited," she recalls. "So we decided to do a series of experiments to see if we could control the fiber formation, and also control its binding to small molecules, which would be housed within the protein's cylinder."

Of special interest were molecules of curcumin, an ingredient in dietary supplements used to combat Alzheimer's disease, cancers and heart disorders.

By adding a set of metal-recognizing amino acids to the coiled-coil protein, the NYU-Poly team succeeded, finding that the nanofibers alter their shapes upon addition of metals such as zinc and nickel to the protein. Moreover, the addition of zinc fortified the nanofibers, enabling them to hold more curcumin, while the addition of nickel transformed the fibers into clumped mats, triggering the release of the drug molecule.

Next, Montclare says, the researchers plan to experiment with creating scaffolds of nanofibers that can be used to induce the regeneration of bone and cartilage (via embedded vitamin D) or human stem cells (via embedded vitamin A).

Later, it may even be possible to apply this organic, protein-based method for creating nanofibers to the world of computers and consumer electronics, Montclare says -- producing nanoscale gold threads for use as circuits in computer chips by first creating the nanofibers and then guiding that metal to them.

Ultimately, Montclare says, the researchers would like the fruits of their discovery -- such therapeutic nanofibers and metallic nanowires -- to be adopted by pharmaceutical companies and microprocessor makers alike.

Funding for this NYU-Poly research was provided by the U.S. Air Force Office of Scientific Research, the U.S. Army Research Office, the U.S. Department of Energy and the National Science Foundation.

Story Source:

The above story is reprinted from materials provided by Polytechnic Institute of New York University.

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

Journal Reference:

Susheel K. Gunasekar, Luona Anjia, Hiroshi Matsui, Jin K. Montclare. Effects of Divalent Metals on Nanoscopic Fiber Formation and Small Molecule Recognition of Helical Proteins. Advanced Functional Materials, 2012; DOI: 10.1002/adfm.201101627