the world of chemistry

Tuesday, April 14, 2009

Structural Defects Introduced Into Carbon Nanotubes Could Lead The Way To Carbon Nanotube Circuits

ScienceDaily (Jan. 15, 2009) — Structural defects introduced into carbon nanotubes could lead the way to carbon nanotube circuits, research led by Vincent Meunier of Oak Ridge National Laboratory's Computer Science and Mathematics Division shows.

Individual carbon nanotubes are excellent conductors of electricity, but that conductivity goes away when they are connected together into circuits because the junctions act as barriers, and the connections are effective insulators.

However, work conducted at the Department of Energy's Center for Nanophase Materials Sciences at ORNL and Mexico's National Laboratory for Nanoscience and Nanotechnology Research shows that imperfections in the carbon lattice structure, which is typically hexagonal, improve conductivity between nanotubes.

The finding could lead to nanoscale circuits that enable more compact and more powerful computers made of carbon nanotube materials that outperform silicon.

The research is published in the journal ACS Nano. The work is supported by the Division of Materials Sciences and Engineering, DOE Office of Basic Energy Sciences.

Adapted from materials provided by DOE/Oak Ridge National Laboratory.

Cerium Oxide Nanotubes Get Noticed

ScienceDaily (Mar. 30, 2006) — Chemists and materials scientists often study "nanotubes" -- capsule-shaped molecules only a few billionths of a meter (nanometers) in width. In nanotube form, many materials take on useful, unique properties, such as physical strength and excellent conductivity. Carbon nanotubes are the most widely investigated variety. Now, in pioneering research, scientists at the U.S. Department of Energy's Brookhaven National Laboratory have created and investigated the properties of nanotubes made of a different, yet equally interesting material: cerium oxide.

Brookhaven chemist Wei-Qiang Han. (Image courtesy of Brookhaven National Laboratory)

"Cerium oxide nanotubes have potential applications as catalysts in vehicle emission-control systems and even fuel cells," says Brookhaven chemist Wei-Qiang Han, the lead scientist involved in the work. "But until very recently, they haven't been studied."

Han and his colleagues are in the midst of ongoing research into the structure and properties of cerium oxide nanotubes. As part of this, they have devised a method to synthesize cerium oxide nanotubes of high quality. First, they allow the compounds cerium nitrate and ammonia hydroxide to chemically react. Initially, this reaction forms "one-dimensional" nanostructures, such as rods and sheets, made of the intermediate product cerium hydroxide. The intermediate product is then quickly cooled to zero degrees Celsius, which freezes those structures into place. By letting the chemical reaction proceed over a long period of time, a process called "aging," the hydrogen is eventually removed from the intermediate product and a large quantity of the desired end product -- cerium oxide nanotubes -- is formed.

Han will explain this synthesis method at the American Chemical Society National Meeting in Atlanta, Georgia. His talk will take place at 3:00 p.m. on Tuesday, March 28, 2006, in Room B403 of the Georgia World Congress Center.

During his talk, Han will also discuss his group's recent study -- how cerium oxide nanotubes release oxygen ions when immersed in a low-oxygen environment, a process that is critical to the nanotubes' effectiveness as catalysts. To do this, the researchers have used several techniques. These include "transmission electron microscopy," a very powerful imaging technique, and two x-ray techniques, which they performed at Brookhaven's National Synchrotron Light Source.

"We're interested in studying oxygen-atom vacancies in cerium oxide nanotubes because, when combined with their other surface features, these vacancies may make them more functional and effective in the applications mentioned," Han said.

This work was funded by the Office of Basic Energy Sciences within the U.S. Department of Energy's Office of Science.

Adapted from materials provided by Brookhaven National Laboratory.

Flower-shaped Nanoparticles May Lead To Better Batteries For Portable Electronics

ScienceDaily (Sep. 16, 2008) — Want more power and longer battery life for that cell phone, laptop, and digital music player? "Flower power" may be the solution. Chemists are reporting development of flower-shaped nanoparticles with superior electronic performance than conventional battery materials.

These "nanoflowers" may power next-generation electronic devices, say the scientists in a report scheduled for the Oct. 8 issue of ACS' Nano Letters, a monthly journal.

Gaoping Cao and colleagues point out that nanoflowers are not new. Researchers have developed various types of flower-shaped nanoparticles using different materials, including manganese oxide, the key metallic ingredient that powers conventional batteries. However, older-generation nanoflowers were not suitable for electronic products of the future, which will demand more power and longer battery life, the researchers say.

In the new study, scientists first grew clusters of carbon nanotubes, strands of pure carbon 50,000 times thinner than a human hair, that are known to have superior electrical conductivity. The scientists then deposited manganese oxide onto the nanotubes using a simple, low-cost coating technique called "electrodeposition," resulting in nano-sized clusters that resemble tiny dandelions under an electron microscope. The result was a battery system with higher energy storage capacity, longer life, and greater efficiency than conventional battery materials, the researchers say.

Journal reference:

Zhang, Hao, Cao, Gaoping, Wang, Zhiyong, Yang, Yusheng, Shi, Zujin, and Gu, Zhennan. Growth of Manganese Oxide Nanoflowers on Vertically-Aligned Carbon Nanotube Arrays for High-Rate Electrochemical Capacitive Energy Storage. Nano Letters, 2008; 8 (9): 2664 DOI: 10.1021/nl800925j

Adapted from materials provided by American Chemical Society, via EurekAlert!, a service of AAAS.

Gold, Copper Nanoparticles Take Center Stage In The Search For Hydrogen Production Catalysts

ScienceDaily (Mar. 29, 2007) — X-ray studies at the U.S. Department of Energy's (DOE) Brookhaven National Laboratory are pointing the way to less costly and more efficient catalysts for improving the performance of fuel cells. The studies, which will be presented by Brookhaven chemist Jose Rodriguez at the 233rd National Meeting of the American Chemical Society, show that copper can be substituted for gold in reactions that keep fuel cells functioning longer while eliminating unwanted byproducts.

Chemist Jose Rodriguez (Credit: Image courtesy of DOE/Brookhaven National Laboratory)

With the goal of efficient fuel cell operation in mind, researchers first need to turn their attention to hydrogen, which is one of the leading energy sources being investigated by scientists sponsored by the DOE as part of its mission to ensure the nation's future energy needs. A major problem facing today's most promising fuel-cell technologies is that the same hydrogen-rich materials feeding the reaction often contain high levels of carbon monoxide (CO), which is formed during hydrogen production. Within a fuel cell, CO "poisons" the expensive platinum catalysts that convert hydrogen into electricity, deteriorating their efficiency over time and requiring their replacement.

Rodriguez will discuss how the use of gold and copper nanoparticles might provide a solution to this problem at the National Meeting. "We're trying to find a catalyst that achieves two things: produces hydrogen while removing a large amount of CO," Rodriguez said.

One way to eliminate the CO byproduct is to combine it with water to produce hydrogen gas and carbon dioxide in a process known as the "water-gas shift" reaction. With the assistance of proper catalysts, the water-shift reaction can convert nearly 100 percent of the CO into carbon dioxide. Using catalyst characterization techniques at Brookhaven's National Synchrotron Light Source (NSLS), Rodriguez and coworkers Jonathan Hanson and Jan Hrbek found that nanoparticles of either gold or copper, supported on a metal, can perform this catalytic role. In particular, they found that the greatest catalytic activity is achieved with extremely small nanoparticles -- less than 4 nanometers (4 billionths of a meter) -- supported on the metal cerium oxide, or ceria.

"Metal nanoparticles alone are not able to do the catalysis," Rodriguez said. "But when you put them on the ceria, you see tremendous catalytic activity."

At the nanoscale, gold has long been known to exhibit chemical reactivity that makes it a potent catalyst. The problem, however, comes with its hefty price tag. "We wanted a material that was less expensive," Rodriguez said. "We wanted to see if we could replace the gold with copper." Using x-ray diffraction, absorption, and spectroscopy studies at the NSLS, Rodriguez's group showed that the substitution is indeed possible. Although gold nanoparticles continue to show the greatest catalytic activity, copper is almost as reactive and its cost is much lower.

This research was funded by the Office of Basic Energy Sciences within the DOE's Office of Science.

Adapted from materials provided by DOE/Brookhaven National Laboratory.

Ceria Nanoparticles Catalyze Reactions For Cleaner-Fuel Future

ScienceDaily (Apr. 2, 2005) — SAN DIEGO, CA - Experiments on ceria (cerium oxide) nanoparticles carried out at the U.S. Department of Energy’s Brookhaven National Laboratory may lead to catalytic converters that are better at cleaning up auto exhaust, and/or to more-efficient ways of generating hydrogen — a promising zero-emission fuel for the future. Brookhaven chemist Jose Rodriguez will present results from two studies exploring the composition, structure, and reactivity of these versatile nanoparticles during the 229th National Meeting of the American Chemical Society on Tuesday, March 15, at 8:15 a.m. in room Del Mar A of the Hyatt Regency, San Diego, California.

After using a novel technique to synthesize the ceria nanoparticles, Rodriguez and coworkers Xianqin Wang and Jonathan Hanson used bright beams of x-rays at the National Synchrotron Light Source to study how their composition, structure, and reactivity changed in response to doping with zirconium in one case, and impregnation with gold in another.

“In a catalytic converter, ceria acts as a buffer, absorbing or releasing oxygen depending on the conditions of the engine to maintain the catalyst in its optimum operating condition for converting harmful emissions such as carbon monoxide and nitrogen oxide to carbon dioxide and nitrogen gas,” Rodriguez said. Others have found that adding zirconium improves ceria’s ability to store and release oxygen.

The synchrotron studies at Brookhaven explain why: Zirconium changes the ceria’s structure to increase the number of oxygen “vacancies” — or places for oxygen uptake and release. Furthermore, Rodriguez says, “the ceria nanoparticles we studied have much better performance, higher chemical reactivity, than the bulk form of ceria currently used in catalytic converters.” Thus, this research holds promise for more-efficient catalytic converters — and cleaner air.

In the second study, Wang, Hanson, and Rodriguez deposited gold on the surface of ceria nanoparticles and used x-rays at the synchrotron to determine the catalyst’s “active phase” — the conformation responsible for the catalytic activity — in the conversion of water and carbon monoxide to hydrogen gas and carbon dioxide. This “water-gas shift” reaction is important for generating hydrogen, which can be used for chemical transformations and as a fuel in a hydrogen-based economy. Hydrogen is one of the leading energy sources being investigated by scientists sponsored by the Department of Energy as part of its mission to ensure the nation’s future energy needs.

“In both cases, we are learning about the fundamental conditions necessary for optimal operation of the catalysts,” Rodriguez said. “This kind of knowledge eventually will lead to a rational design of even more effective catalysts.”

This research was funded by the Office of Basic Energy Sciences within the U.S. Department of Energy’s Office of Science.

Adapted from materials provided by Brookhaven National Laboratory.

Nanoparticle Offers Promise For Treating Glaucoma

ScienceDaily (June 19, 2007) — A unique nanoparticle made in a laboratory at the University of Central Florida is proving promising as a drug delivery device for treating glaucoma, an eye disease that can cause blindness and affects millions of people worldwide.

Glaucoma affects millions of people and if left untreated can cause blindness. (Credit: Jerry Klein)

“The nanoparticle can safely get past the blood-brain barrier making it an effective non-toxic tool for drug delivery,” said Sudipta Seal, an engineering professor with appointments in UCF’s Advanced Materials Processing and Analysis Center and the Nanoscience Technology Center.

Seal and his colleagues from North Dakota State University note in the article that while barely 1-3 percent of existing glaucoma medicines penetrate into the eye, earlier experiments with nanoparticles have shown not only high penetration rates but also little patient discomfort. The miniscule size of the nanoparticles makes them less abrasive than some of the complex polymers now used in most eye drops.

Seal and his team created a specialized cerium oxide nanoparticle and bound it with a compound that has been shown to block the activity of an enzyme (hCAII) believed to play a central role in causing glaucoma.

The disease involves abnormally high pressure of the fluid inside the eye, which, if left untreated, can result in damage to the optic nerve and vision loss. High pressure occurs, in part, because of a buildup of carbon dioxide inside the eye, and the compound blocks the enzyme that produces carbon dioxide.

Seal and a team of collaborators including Sanku Mallik, of North Dakota State University, developed the research on using nanoparticles as a delivery mechanism for the compound after supervising a student summer project at UCF. Duke University undergraduate Serge Reshetnikov spent a summer studying nanoscience on UCF’s Orlando campus as part of a Research Experience for Undergraduates (REU) project funded by the National Science Foundation. Reshetnikov started looking into the possibilities of using nanoparticles as drug delivery tools. Subsequent research with his advisors led to the specific application for glaucoma.

In their paper on the research, which was also supported by the National Science Foundation, Seal and Mallik note the results are “very promising” and that their nanoparticle configuration offers seemingly limitless possibilities as a non-toxic drug delivery tool.

The findings will be published in an article appearing in the June 28 issue of the Journal of Physical Chemistry C.

Adapted from materials provided by University of Central Florida.

Tracking Down The Effect Of Nanoparticles

ScienceDaily (Apr. 12, 2009) — Cerium oxide is a ceramic nano-abrasive. Scientists have now examined, under conditions close to reality, what happens when it is breathed in and deposited on the lung surface. Initially, the result was rather reassuring.

Cell cultures of lung epithelial cells (in the right-hand box) were exposed to an aerosol of cerium oxide nanoparticles in a special glove box. During the exposure of the cell cultures, the nanoparticles were freshly produced by flame synthesis in the left half of the box. (Credit: Image courtesy of ETH Zurich)

Synthetic nanoparticles are ubiquitous in today's world: either as an additive to building materials, whose properties they improve; in cosmetics, mainly in sun creams and toothpaste; or in foodstuffs, to thicken them or brighten their color. However, nano-safety research, i.e. knowledge of how nanoparticles interact with their environment and specifically with a living organism, is still largely in its infancy.

However, this is one of the central topics for the research group led by Wendelin Stark, Assistant Professor at the Institute for Chemical and Bio-engineering of ETH Zurich. The group carries out tests over and over again to investigate the effect nanoparticles have on their surroundings.

Conditions close to reality

Together with the research group led by Peter Gehr, Professor of Histology at the University of Bern, the scientists have now used a completely new method and a new type of lung cell culture to examine how cerium oxide nanoparticles act on the cells. The aim was to study the toxicity of cerium oxide, which is used in large amounts as an abrasive, mainly in the manufacture of semiconductor chips. Although, as a rule, this takes place in a hermetically sealed room from which people are excluded, the researchers now simulated a situation in which ceramic nanomaterial is inhaled directly, for example if nanoparticles are manufactured without protection or the powder is handled incorrectly.

The researchers did this by using what is called flame spray synthesis to spray cerium oxide nanoparticles in a closed glove box, thus simulating aerosols. A fan distributed the aerosols uniformly in the box, about 2.5 cubic meters in size, in which the aerosols were sprayed on to the cultured lung cells for ten, twenty and thirty minutes. The ETH researches hit upon the idea when they spoke to Barbara Rothen-Rutishauser, a scientist from Bern and first author of the paper. She told them about the new type of cell culture.

The innovative aspect of the method is the special cell culture combined with the use of flame spray synthesis. The cell culture of lung epithelial cells grows on a permeable membrane. The lower surface of the epithelial cells is immersed in a medium and their upper surface is covered with a natural liquid layer. Thus the cell culture is very similar to the surface of the lung. As a result of the aerosol production, the spray process is also close to reality. The combination of these two techniques showed how inhaled nanoparticles are deposited on the lung surface. In conventional methods for such experiments up to now, cell cultures were bathed in nanoparticle solutions. However, this can cause the nanoparticles to agglomerate, which alters their properties; moreover, the lung surface is wet in a different way. Consequently, the behavior of the cells might also change.

No cell death

The scientists chose cerium oxide for their study, mainly because the material does not occur physiologically in cells, meaning that only the effect of the nanoparticle on the cell is observed. The longer the cultures were sprayed for, the more nanoparticles were deposited on the lung cells. The scientists observed that the cells were not destroyed, i.e. they did not die. However, the permeability of the cell layer increased. Therefore, the researchers suspect that certain structures of particular proteins that seal the interstices between the epithelial cells had altered under the influence of the nanoparticles. The production of a substance in the cell which is associated with oxidative stress and which could result in DNA damage could also be observed.

Long-term effects unknown

Robert Grass, group leader in Wendelin Stark’s group, explains: “However, we were unable to observe the effect of the particles on the cells over a prolonged time.” This is because the cultures must be subjected to further processing to allow them to be examined under a microscope. In a next step, the researchers plan to replicate even more realistic conditions by using what are known as triple cell co-cultures that simulate human cellular respiratory tract barriers. For example, they want to find out how the body’s phagocytes and “waste disposal agents”, known as macrophages, deal with nanoparticles.