By Michael Berger. Copyright ©
Nanowerk (Nanowerk Spotlight) The construction of artificial micro- and nanomotors is a high priority in the nanotechnology field owing to their great potential for diverse potential applications, ranging from targeted drug delivery, on-chip diagnostics and biosensing, or pumping of fluids at the microscale to environmental remediation.
Particular attention has been given to self-propelled chemically-powered micro/nanoscale motors, such as catalytic nanowires (read more: “”Another nanotechnology step towards ‘Fantastic Voyage'”), microtube engines (read more: “Microbots transport, assemble and deliver micro- and nanoscale objects”) or spherical Janus microparticles (read more: “Novel motor system powered by polymerization”). In new work, researchers in Germany have now reported the first example of micromotors for the active degradation of organic pollutants in solution. The novelty of this work lies in the synergy between internal and external functionality of the micromotors.
“Previously, some groups tried to demonstrate the use of catalytic nanomotors for biomedical applications – including ours – on-chip biosensors and capture of bio species,” Dr. Samuel Sánchez, Group Leader Smart Nano-Bio-Systems, Max Planck Institute for Intelligent Systems, tells Nanowerk. “However, the toxicity of the fuel employed still limits their real applications. We imagined that environmental applications might be another field to explore, where the use of hydrogen peroxide is not controversial.” In that direction, Wang’s group reported the removal of oil droplets (“‘Microsubmarines’ designed to help clean up oil spills”) from solution, not degrading them.
Now, Sánchez and his collaborators went one step beyond that and demonstrated the total removal of contaminants using micromotors. Indeed, the chemical is used for the self-propulsion and for the remediation when interacts with the outer layer of the micromachine. “We have demonstrated the ability of self-propelled micromotors to oxidize organic pollutants in aqueous solutions through a Fenton process,” explains Sánchez. “The combination of mixing and releasing iron ions in liquids results in a rate of removal of model pollutant (rhodamine 6G) ca. 12 times higher than when the Fenton oxidation process is carried out with nonpropelling metallic iron tubes.”
Reporting their results in The November 1, 2013 online edition of ACS Nano (“Self-Propelled Micromotors for Cleaning Polluted Water”), the research team from Max Planck, the Leibniz Institute for Solid State and Materials Research Dresden, and the Chemnitz University of Technology demonstrates that micromotors boost the Fenton oxidation process (read more about Fenton reactions at the bottom of this article) without applying external energy, and complete degradation of organic pollutants is achieved.
Schematic process for the degradation of polluted water (rhodamine 6G as model contaminant) into inorganic products by multifunctional micromotors. The self propulsion is achieved by the catalytic inner layer (Pt), which provides the motion of the micromotors in H2O2 solutions. The remediation of polluted water is achieved by the combination of Fe2+ ions with peroxide, generating OH• radicals, which degrade organic pollutants. (Reprinted with permission from American Chemical Society)
Sánchez notes that, if desired, the micromotors can be easily recovered using a magnet once the water purification process has been completed and the excess of hydrogen peroxide can be easily decomposed to pure water and oxygen under visible light. The team fabricated their tubular bubble-propelled micromotors containing small amounts of metallic iron (from 20 to 200 nm layer thickness) as outer layer and platinum as inner layer. The mechanism of degradation is based on Fenton reactions relying on spontaneous acidic corrosion of the iron metal surface of the micromotors in the presence of hydrogen peroxide, which acts both as a reagent for the Fenton reaction and as main fuel to propel the micromotors.
Moreover, the ability of self-propelled, tubular micromotors to improve mixing results in a synergetic effect that enhances water remediation without applying external energy. This work can pave the way for the use of multifunctional micromotors for environmental applications where the use of hydrogen peroxide is not a major drawback but a co-reagent. Sánchez adds that the high efficiency of the oxidation of organic pollutants achieved by the Fe/Pt catalytic micromotors reported in this work is of importance for the design of new and faster water treatments, such as the decontamination of organic compounds in wastewaters and industrial effluents. The aim of this study was to fabricate an autonomous microscopic cleaning system that is working without external energy input in a much faster and convenient way.
The micromotors offer this ability to move the catalyst around without external actuation or addition of catalyst (iron salts) to achieve water remediation, removal of organic dyes, etc. However, as the researchers point out, this is an application especially for microscale environments. “It is, unfortunately, clear that we would not use the micromotors in a large reactor vessel to clean huge amounts of water,” says Sánchez. Nevertheless, the high efficiency of the oxidation of organic pollutants achieved by the Fe/Pt catalytic micromotors reported here is of importance for the design of new and faster water treatments, such as the decontamination of organic compounds in wastewaters and industrial effluents. “We have proven that the usefulness of the micromotors lies not solely in their capacity to move, but to exploit their motion using their external surface to enhance useful catalytic reactions,” says Sánchez. “This work could open a new research line towards coupling a variety of catalytic reactions in self-propelled devices where the presence of hydrogen peroxide is not a disadvantage. We expect that a rich variety of contaminants can be in the next years be cleaned.”
Watch Short Video Here:
Watch the micromotor in action. A synergetic effect is achieved taking advantage of the release of the iron ions from the outer layer of the micromotors and their active motion in the solution.
About Fenton reactions The Fenton method is one of the most popular advanced oxidation processes for the degradation of organic pollutants, utilizing the hydroxyl radical (OH•) as its main oxidizing agent. The generation of OH• in the Fenton method occurs by reaction of H2O2 in the presence of Fe(II). However, one disadvantage of these processes is that Fe ions in solution must be removed after the treatment to meet regulations for drinking water. In order to diminish and, in the best scenario, solve the problems caused by the presence of Fe ions in treated effluents and decrease the costs of recovery, the use of heterogeneous Fenton catalysts is a promising strategy that could allow for the degradation of pollutants by Fenton processes without the requirement of dissolved iron salts. The micromotors fabricated in this work can be included as a new type of heterogeneous Fenton catalyst. With this method the remaining iron in the solution is one to three orders of magnitude lower than in conventional Fenton processes.
Read more: http://www.nanowerk.com/spotlight/spotid=33493.php#ixzz2mN10wW9l
The 7″ display includes a Quantum Dot Enhancement Film (QDEF) produced by 3M in collaboration with Nanosys, Inc. Compared to the traditional LED-LCD display, the QDEF essentially replaces the YAG phosphor of the white LED backlight and functions as a high-efficiency photoluminescent emitter. The ODEF includes quantum dots of different sizes, which would emit different colors when excited due to quantum confinement effect. More detail of the QDEF can be found via the link below.
It is noted that the quantum-dot-enhanced display of Kindle Fire HDX 7 does not utilize the electroluminescent property of quantum dots, and thus is not actually a quantum dot light emitting diode (QLED). Nevertheless, it could signal the beginning of the mass commercialization of quantum dots technology in consumer markets.
And the “very best” of today’s display technologies according to Displaymate, quote,
“The very best of today’s display technologies? The Quantum Dots displays used in the Kindle Fire HDX 7 according to the report.
Quantum Dots are almost magical because they use Quantum Physics to produce highly saturated primary colors for LCDs that are similar to those produced by OLED displays. They not only significantly increase the size of the Color Gamut by 40-50 percent but also improve the power efficiency by an additional 15-20 percent. Instead of using White LEDs (which have yellow phosphors) that produce a broad light spectrum that makes it hard to efficiently produce saturated colors, Quantum Dots directly convert the light from Blue LEDs into highly saturated primary colors for LCDs. You can see the remarkable difference in their light spectra in Figure 4. Quantum Dots are going to revolutionize LCDs for the next 5+ years.”
The content of this article is intended to provide a general guide to the subject matter. Specialist advice should be sought about your specific circumstances.
How does QDEF work?
Nanosys QDEF™ enables deep color and high efficiency by providing displays with an ideal light source. How does it do that?
Each sheet of QDEF contains trillions of tiny (by tiny we mean: a bit bigger than a water molecule but smaller than a virus in size) nanoscrystal phosphors, called “Quantum Dots .” Not found naturally occurring anywhere on Earth, these “dots” can be tuned, by changing their size, to emit light at just the right wavelengths for our displays and do so very efficiently.
Unlike conventional phosphor technologies such as YAG that emit with a fixed spectrum, quantum dots can actually convert light to nearly any color in the visible spectrum. Pumped with a blue source, such as the GaN LED, they can be made to emit at any wavelength beyond the pump source wavelength with very high efficiency (over 90% quantum yield) and with very narrow spectral distribution (only 30 – 40nm FWHM.) The real magic of quantum dots is in the ability to tune the color output of the dots, by carefully controlling the size of the crystals as they are synthesized so that their spectral peak output can be controlled within 2 nanometers to nearly any visible wavelength.
For the first time, display designers will have the ability to tune and match the backlight spectrum to the color filters. This means displays that are brighter, more efficient, and produce truly vibrant colors.
How does it all come together?
Engineering the quantum dots to precise display industry specifications isn’t enough to revolutionize the way LCDs are experienced on its own. The dots need to be easily integrated into current manufacturing operations with minimal impact on display system design if they are to be widely adopted. To do this, Nanosys spent a lot of time working with major display manufacturers to get the packaging just right so that it would be a simple, drop-in product that did not require any line retooling or process changes. The end result is called Quantum Dot Enhancement Film or QDEF.
Designed as a replacement for the an existing film in LCD backlights called the diffuser, QDEF combines red and green emitting quantum dots in a thin, optically clear sheet that emits white light when stimulated by blue (some of that blue is allowed to pass through to make the B in RGB at the LCM of course). So manufacturers who’ve invested billions in plant and equipment for LCD production can simply slip this sheet into their process, change their ‘white’ LEDs to blue (the same LEDs but without the phosphor) and start producing LCD panels with the colors and efficiencies of the best OLEDs, at a fraction of the cost and current industrial scale.
Nanosys is currently shipping production samples to display manufacturers and is on track to begin producing at commercial volumes fall of 2013.
|(Nanowerk News) Jeong-Yeol Yoon, associate professor of agricultural and biosystems engineering, and Dr. Marvin Slepian, professor of cardiology and biomedical engineering, collaborated to test how nanotechnology-based techniques can be used to better facilitate adhesion between tissue and implanted devices.|
|“When we created the nanotexture surface, we thought it could be used as a sticky surface for the implants,” Yoon says.|
|Cell-substrate adhesion involves the interplay of mechanical properties, surface topographic features, electrostatic charge and biochemical mechanisms. By working at the nanoscale level, Yoon was able to maximize the physical properties of the underlying substrate in promoting adhesion.|
|But beyond simply creating a sticky surface, the researchers’ goal was to create a selectively sticky surface, favoring endothelial cell attachment, without favoring platelet attachment, Slepian says.|
|The connection between Yoon, a specialist in biosensors and nanotechnology from the College of Agriculture and Life Sciences, and Slepian, co-founder and chief scientific officer of artificial-heart manufacturer SynCardia, came about by chance. A graduate student in Yoon’s lab met Slepian through their shared interest in bicycling.|
|“It’s very rare for the agriculture people to work with the cardiovascular people in the medical school,” Yoon says.|
|But their research specialties clicked.|
|One particular challenge to overcome in cardiovascular implants is the potential for devices – such as stents placed inside coronary arteries – to become detached as a result of blood flow, Yoon says.|
|“We’re particularly focused on the cardiovascular applications because there’s a blood flow involved and our system is very good when there’s a flow situation,” Yoon says.|
|The results of the study, published in the journal Advanced Healthcare Materials (“Nanowell-Trapped Charged Ligand-Bearing Nanoparticle Surfaces: A Novel Method of Enhancing Flow-Resistant Cell Adhesion”), reveal that the researchers’ strategy leads to enhanced endothelial cell adhesion under both static and flow conditions.|
|The adhesive properties derive from optimized surface texturing, electrostatic charge and cell adhesive ligands (molecular binding substances) that are uniquely assembled on the substrata surface as an ensemble of nanoparticles trapped in nanowells.|
|“There are lot of other people out there who use nanotechnology for improving the implants, but this is stronger than other adhesive methods using nanotechnology,” Yoon says.|
|“Obviously it can be used for everything else – lungs, digestive track and other systems. There are lots of other opportunities we haven’t explored,” he says.|
|The research is a perfect fit for Advanced Healthcare Materials, a new journal that spun off from the longstanding Advanced Materials journal.|
|“The use of the materials for the health care applications is probably the hottest area in materials science and engineering,” Yoon says. “We believe the journal will become even stronger than the mother journal.”|
|Just as the new journal marks an exciting intersection of disciplines, Yoon says the environment at the UA encourages such interdisciplinary approaches.|
|“I joined the University of Arizona because there are so many interdisciplinary activities going on. I see a lot of collaboration between departments in the same college at other universities, but at the University of Arizona, the environment is more open and you see collaboration across colleges,” Yoon says.|
|Slepian agreed, saying the pair has already filed grant applications for future work together.|
|“It has been fun and exciting to have an interdisciplinary collaborator,” he says.|
|Source: University of Arizona|
|(Nanowerk News) Chemical engineers at Rice University have found a new catalyst that can rapidly break down nitrites, a common and harmful contaminant in drinking water that often results from overuse of agricultural fertilizers.|
|Nitrites and their more abundant cousins, nitrates, are inorganic compounds that are often found in both groundwater and surface water. The compounds are a health hazard, and the Environmental Protection Agency places strict limits on the amount of nitrates and nitrites in drinking water. While it’s possible to remove nitrates and nitrites from water with filters and resins, the process can be prohibitively expensive.|
|Researchers at Rice University’s Catalysis and Nanomaterials Laboratory have found that gold and palladium nanoparticles can rapidly break down nitrites.|
|“This is a big problem, particularly for agricultural communities, and there aren’t really any good options for dealing with it,” said Michael Wong, professor of chemical and biomolecular engineering at Rice and the lead researcher on the new study. “Our group has studied engineered gold and palladium nanocatalysts for several years. We’ve tested these against chlorinated solvents for almost a decade, and in looking for other potential uses for these we stumbled onto some studies about palladium catalysts being used to treat nitrates and nitrites; so we decided to do a comparison.”|
|Catalysts are the matchmakers of the molecular world: They cause other compounds to react with one another, often by bringing them into close proximity, but the catalysts are not consumed by the reaction.|
|In a new paper in the journal Nanoscale (“Supporting palladium metal on gold nanoparticles improves its catalysis for nitrite reduction “), Wong’s team showed that engineered nanoparticles of gold and palladium were several times more efficient at breaking down nitrites than any previously studied catalysts. The particles, which were invented at Wong’s Catalysis and Nanomaterials Laboratory, consist of a solid gold core that’s partially covered with palladium.|
|Over the past decade, Wong’s team has found these gold-palladium composites have faster reaction times for breaking down chlorinated pollutants than do any other known catalysts. He said the same proved true for nitrites, for reasons that are still unknown.|
|“There’s no chlorine in these compounds, so the chemistry is completely different,” Wong said. “It’s not yet clear how the gold and palladium work together to boost the reaction time in nitrites and why reaction efficiency spiked when the nanoparticles had about 80 percent palladium coverage. We have several hypotheses we are testing out now. “|
|He said that gold-palladium nanocatalysts with the optimal formulation were about 15 times more efficient at breaking down nitrites than were pure palladium nanocatalysts, and about 7 1/2 times more efficient than catalysts made of palladium and aluminum oxide.|
|Wong said he can envision using the gold-palladium catalysts in a small filtration unit that could be attached to a water tap, but only if the team finds a similarly efficient catalyst for breaking down nitrates, which are even more abundant pollutants than nitrites.|
|“Nitrites form wherever you have nitrates, which are really the root of the problem,” Wong said. “We’re actively studying a number of candidates for degrading nitrates now, and we have some positive leads.”|
|Source: Rice University|
Berkeley Lab Researchers Use Fluorescent Tetrapod Quantum Dots to Measure the Mechanical Strength of Polymer Fibers
Fluorescent tetrapod nanocrystals could light the way to the future design of stronger polymer nanocomposites. A team of researchers with the U.S. Department of Energy (DOE)’s Lawrence Berkeley National Laboratory (Berkeley Lab) has developed an advanced opto-mechanical sensing technique based on tetrapod quantum dots that allows precise measurement of the tensile strength of polymer fibers with minimal impact on the fiber’s mechanical properties.
In a study led by Paul Alivisatos, Berkeley Lab director and the Larry and Diane Bock Professor of Nanotechnology at the University of California (UC) Berkeley, the research team incorporated into polymer fibers a population of tetrapod quantum dots (tQDs) consisting of a cadmium-selenide (CdSe) core and four cadmium sulfide (CdS) arms. The tQDs were incorporated into the polymer fibers via electrospinning, among today’s leading techniques for processing polymers, in which a large electric field is applied to droplets of polymer solution to create micro- and nano-sized fibers. This is the first known application of electrospinning to tQDs.
Fluorescent tetrapod quantum dots or tQDs (brown) serve as stress probes that allow precise measurement of polymer fiber tensile strength with minimal impact on mechanical properties. Inserts show relaxed tQDs (upper) and stressed tQDs (lower).
“The electrospinning process allowed us to put an enormous amount of tQDs, up to 20-percent by weight, into the fibers with minimal effects on the polymer’s bulk mechanical properties,” Alivisatos says. “The tQDs are capable of fluorescently monitoring not only simple uniaxial stress, but stress relaxation and behavior under cyclic varying loads. Furthermore, the tQDs are elastic and recoverable, and undergo no permanent change in sensing ability even upon many cycles of loading to failure.”
Alivisatos is the corresponding author of a paper describing this research in the journal NANO Letters titled “Tetrapod Nanocrystals as Fluorescent Stress Probes of Electrospun Nanocomposites.” Coauthors were Shilpa Raja, Andrew Olson, Kari Thorkelsson, Andrew Luong, Lillian Hsueh, Guoqing Chang, Bernd Gludovatz, Liwei Lin, Ting Xu and Robert Ritchie.
From left, Andrew Olson, Shilpa Raja and Andrew Luong are members of Paul Alivisatos’s research group who used electrospinning to incorporate tetrapod quantum dot stress probes into polymer fibers. (Photo by Roy Kaltschmidt)
Polymer nanocomposites are polymers that contain fillers of nanoparticles dispersed throughout the polymer matrix. Exhibiting a wide range of enhanced mechanical properties, these materials have great potential for a broad range of biomedical and material applications. However, rational design has been hampered by a lack of detailed understanding of how they respond to stress at the micro- and nanoscale.
“Understanding the interface between the polymer and the nanofiller and how stresses are transferred across that barrier are critical in reproducibly synthesizing composites,” Alivisatos says. “All of the established techniques for providing this information have drawbacks, including altering the molecular-level composition and structure of the polymer and potentially weakening mechanical properties such as toughness. It has therefore been of considerable interest to develop optical luminescent stress-sensing nanoparticles and find a way to embed them inside polymer fibers with minimal impact on the mechanical properties that are being sensed.”
The Berkeley Lab researchers met this challenge by combining semiconductor tQDs of CdSe/CdS, which were developed in an earlier study by Alivisatos and his research group, with electrospinning. The CdSe/CdS tQDs are exceptionally well-suited as nanoscale stress sensors because an applied stress will bend the arms of the tetrapods, causing a shift in the color of their fluorescence. The large electric field used in electrospinning results in a uniform dispersal of tQD aggregates throughout the polymer matrix, thereby minimizing the formation of stress concentrations that would act to degrade the mechanical properties of the polymer. Electrospinning also provided a much stronger bond between the polymer fibers and the tQDs than a previous diffusion-based technique for using tQDs as stress probes that was reported two years ago by Alivisatos and his group. Much higher concentrations of tQDs could also be a achieved with electrospinning rather than diffusion.
When stress was applied to the polymer nanocomposites, elastic and plastic regions of deformation were easily observed as a shift in the fluorescence of the tQDs even at low particle concentrations. As particle concentrations were increased, a greater fluorescence shift per unit strain was observed. The tQDs acted as non-perturbing probes that tests proved were not adversely affecting the mechanical properties of the polymer fibers in any significant way.
“We performed mechanical tests using a traditional tensile testing machine with all of our types of polymer fibers,” says Shilpa Raja, a lead author of the Nano Letters paper along with Andrew Olson, both members of Alivisatos’ research group. “While the tQDs undoubtedly change the composition of the fiber – it is no longer pure polylactic acid but instead a composite – we found that the mechanical properties of the composite and crystallinity of the polymer phase show minimal change.”
The research team believes their tQD probes should prove valuable for a variety of biological, imaging and materials engineering applications.
“A big advantage in the development of new polymer nanocomposites would be to use tQDs to monitor stress build-ups prior to material failure to see how the material was failing before it actually broke apart,” says co-lead author Olson. “The tQDs could also help in the development of new smart materials by providing insight into why a composite either never exhibited a desired nanoparticle property or stopped exhibiting it during deformation from normal usage.”
For biological applications, the tQD is responsive to forces on the nanoNewton scale, which is the amount of force exerted by living cells as they move around within the body. A prime example of this is metastasizing cancer cells that move through the surrounding extracellular matrix. Other cells that exert force include the fibroblasts that help repair wounds, and cardiomyocytes, the muscle cells in the heart that beat.
“All of these types of cells are known to exert nanoNewton forces, but it is very difficult to measure them,” Raja says.
“We’ve done preliminary studies in which we have shown that cardiomyocytes on top of a layer of tQDs can be induced to beat and the tQD layer will show fluorescent shifts in places where the cells are beating. This could be extended to a more biologically-relevant environment in order to study the effects of chemicals and drugs on the metastasis of cancer cells.”
Another exciting potential application is the use of tQDs to make smart polymer nanocomposites that can sense when they have cracks or are about to fracture and can strengthen themselves in response.
“With our technique we are combining two fields that are usually separate and have never been combined on the nanoscale, optical sensing and polymer nanocomposite mechanical tunability,” Raja says. “As the tetrapods are incredibly strong, orders of magnitude stronger than typical polymers, ultimately they can make for stronger interfaces that can self-report impending fracture.”
This research was primarily supported by the DOE Office of Science.
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Lawrence Berkeley National Laboratory addresses the world’s most urgent scientific challenges by advancing sustainable energy, protecting human health, creating new materials, and revealing the origin and fate of the universe. Founded in 1931, Berkeley Lab’s scientific expertise has been recognized with 13 Nobel prizes. The University of California manages Berkeley Lab for the U.S. Department of Energy’s Office of Science. For more, visit www.lbl.gov.
DOE’s Office of Science is the single largest supporter of basic research in the physical sciences in the United States, and is working to address some of the most pressing challenges of our time. For more information, please visit the Office of Science website at science.energy.gov/.
For more about the research of Paul Alivisatos go here
|Source: American Associates, Ben-Gurion University of the Negev|
18 Nov 2013
Menlo Park, Calif. — Researchers have made the first battery electrode that heals itself, opening a new and potentially commercially viable path for making the next generation of lithium ion batteries for electric cars, cell phones and other devices. The secret is a stretchy polymer that coats the electrode, binds it together and spontaneously heals tiny cracks that develop during battery operation, said the team from Stanford University and the Department of Energy’s (DOE) SLAC National Accelerator Laboratory.
They report the advance in the Nov. 19 issue of Nature Chemistry.
This prototype lithium ion battery, made in a Stanford lab, contains a silicon electrode protected with a coating of self-healing polymer. The cables and clips in the background are part of an apparatus for testing the performance of batteries during multiple charge-discharge cycles. (Brad Plummer/SLAC)
“Self-healing is very important for the survival and long lifetimes of animals and plants,” said Chao Wang, a postdoctoral researcher at Stanford and one of two principal authors of the paper. “We want to incorporate this feature into lithium ion batteries so they will have a long lifetime as well.”
Chao developed the self-healing polymer in the lab of Stanford Professor Zhenan Bao, whose group has been working on flexible electronic skin for use in robots, sensors, prosthetic limbs and other applications. For the battery project he added tiny nanoparticles of carbon to the polymer so it would conduct electricity.
”We found that silicon electrodes lasted 10 times longer when coated with the self-healing polymer, which repaired any cracks within just a few hours,” Bao said.
“Their capacity for storing energy is in the practical range now, but we would certainly like to push that,” said Yi Cui, an associate professor at SLAC and Stanford who led the research with Bao. The electrodes worked for about 100 charge-discharge cycles without significantly losing their energy storage capacity. “That’s still quite a way from the goal of about 500 cycles for cell phones and 3,000 cycles for an electric vehicle,” Cui said, “but the promise is there, and from all our data it looks like it’s working.”
Researchers worldwide are racing to find ways to store more energy in the negative electrodes of lithium ion batteries to achieve higher performance while reducing weight. One of the most promising electrode materials is silicon; it has a high capacity for soaking up lithium ions from the battery fluid during charging and then releasing them when the battery is put to work.
But this high capacity comes at a price: Silicon electrodes swell to three times normal size and shrink back down again each time the battery charges and discharges, and the brittle material soon cracks and falls apart, degrading battery performance. This is a problem for all electrodes in high-capacity batteries, said Hui Wu, a former Stanford postdoc who is now a faculty member at Tsinghua University in Beijing, the other principal author of the paper.
To make the self-healing coating, scientists deliberately weakened some of the chemical bonds within polymers – long, chain-like molecules with many identical units. The resulting material breaks easily, but the broken ends are chemically drawn to each other and quickly link up again, mimicking the process that allows biological molecules such as DNA to assemble, rearrange and break down.
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To show how flexible their self-healing polymer is, researchers coated a balloon with it and then inflated and deflated the balloon repeatedly, mimicking the swelling and shrinking of a silicon electrode during battery operation. The polymer stretches but does not crack. (Brad Plummer/SLAC)
Researchers in Cui’s lab and elsewhere have tested a number of ways to keep silicon electrodes intact and improve their performance. Some are being explored for commercial uses, but many involve exotic materials and fabrication techniques that are challenging to scale up for production.
The self-healing electrode, which is made from silicon microparticles that are widely used in the semiconductor and solar cell industries, is the first solution that seems to offer a practical road forward, Cui said. The researchers said they think this approach could work for other electrode materials as well, and they will continue to refine the technique to improve the silicon electrode’s performance and longevity.
The research team also included Zheng Chen and Matthew T. McDowell of Stanford. Cui and Bao are members of the Stanford Institute for Materials and Energy Sciences, a joint SLAC/Stanford institute. The research was funded by DOE through SLAC’s Laboratory Directed Research and Development program and by the Precourt Institute for Energy at Stanford University.
SLAC is a multi-program laboratory exploring frontier questions in photon science, astrophysics, particle physics and accelerator research. Located in Menlo Park, California, SLAC is operated by Stanford University for the U.S. Department of Energy Office of Science. To learn more, please visit www.slac.stanford.edu.
The Stanford Institute for Materials and Energy Sciences (SIMES) is a joint institute of SLAC National Accelerator Laboratory and Stanford University. SIMES studies the nature, properties and synthesis of complex and novel materials in the effort to create clean, renewable energy technologies. For more information, please visit simes.slac.stanford.edu.
DOE’s Office of Science is the single largest supporter of basic research in the physical sciences in the United States, and is working to address some of the most pressing challenges of our time. For more information, please visit science.energy.gov.
15 Nov 2013
Scientists collaborate to maximize energy gains from tiny nanoparticles
“We are developing a new ‘micro-reactor’ that enables us to explore many aspects of catalytic function using multiple approaches at Brookhaven’s National Synchrotron Light Source (NSLS), the soon-to-be-completed NSLS-II, and the Center for Functional Nanomaterials (CFN),” said Stach, who works at the CFN. “This approach lets us understand multiple aspects of how catalysts work so that we can tweak their design to improve their function. This work could lead to big gains in energy efficiency and cost savings for industrial processes.” – Anatoly Frenkel, Yeshiva University
Sometimes big change comes from small beginnings. That’s especially true in the research of Anatoly Frenkel, a professor of physics at Yeshiva University, who is working to reinvent the way we use and produce energy by unlocking the potential of some of the world’s tiniest structures: nanoparticles.
“The nanoparticle is the smallest unit in most novel materials, and all of its properties are linked in one way or another to its structure,” said Frenkel. “If we can understand that connection, we can derive much more information about how it can be used for catalysis, energy, and other purposes.”
“This work could lead to big gains in energy efficiency and cost savings for industrial processes.”
— Eric Stach, CFN
Frenkel is collaborating with materials scientist Eric Stach and others at the U.S. Department of Energy’s Brookhaven National Laboratory to develop new ways to study how nanoparticles behave in catalysts—the “kick-starters” of chemical reactions that convert fuels to useable forms of energy and transform raw materials to industrial products.
“We are developing a new ‘micro-reactor’ that enables us to explore many aspects of catalytic function using multiple approaches at Brookhaven’s National Synchrotron Light Source (NSLS), the soon-to-be-completed NSLS-II, and the Center for Functional Nanomaterials (CFN),” said Stach, who works at the CFN. “This approach lets us understand multiple aspects of how catalysts work so that we can tweak their design to improve their function. This work could lead to big gains in energy efficiency and cost savings for industrial processes.”
High-tech tools for science
Until now, the methods for understanding catalytic properties could only be used one at a time, with the catalyst ending up in a different state for each of the experiments. This made it difficult to compare information obtained using the different instruments. The new micro-reactor will employ multiple techniques—microscopy, spectroscopy, and diffraction—to examine different properties of catalysts simultaneously under operating conditions. By keeping particles in the same structural and dynamic state under the same reaction conditions, the micro-reactor will give scientists a much better sense of how they function.
“These developments have resulted from the combination of unique facilities available at Brookhaven,” said Frenkel. “By working closely with Eric, we realized that there was a way to make both x-ray and electron-based methods work in a truly complementary fashion.
Each technique has strengths, Stach explained. “At the NSLS, using powerful beams of x-rays, we can tell how the entire group of nanoparticles behaves, while electron microscopy at the CFN lets us see the atomic structure of each nanoparticle. By having both of these views of the catalysts we can more clearly understand the relationship between catalyst structure and function.”
Said Frenkel, “It was very satisfying for us to conduct the first tests with the reactor at each facility and receive positive results. I am particularly grateful to Ryan Tappero, the scientist who runs NSLS beamline X27A, for his expert help with x-ray data acquisition.”
Frenkel has had an ongoing collaboration with scientists at Brookhaven. Last year, with post-doctoral research associate Qi Wang, Frenkel and Stach measured properties of nanoparticles using the x-rays produced by the NSLS as well as atomic-scale imaging with electrons at the CFN. As reported in a paper published in the Journal of the American Chemical Society earlier this year, they discovered that rather than changing completely from one state to another at a certain temperature and size, as had been previously believed, there is a transition zone between states when particles are changing forms.
“This is of significance fundamentally because until now, the structures were known to merely change from one form to another—they were never envisioned to coexist in different forms,” Frenkel said. “With our information we can explain why catalysts often don’t work as expected and how to improve them.”
Training for young scientists
The collaboration also offers opportunities for students to experience the challenges of research, giving them access to the world-class tools at Brookhaven. Frenkel’s undergraduate students at Yeshiva University’s Stern College for Women help with measurements, data analysis, and interpretation, and many have already accompanied him to Brookhaven to assist in his work using NSLS and other cutting-edge instruments.
“I’m giving them firsthand experience about what a researcher’s life is like early on as they conduct first-rate research,” said Frenkel. “This experience opens doors to any field they want to be in.”
Alyssa Lerner, a pre-engineering major who has been working with Frenkel at Brookhaven, said the research “has helped me develop skills like computational analysis and critical thinking, which are essential in any scientific field. The hands-on experimental experience has given me a better understanding of how the scientific community operates, helping me make more informed career-related choices as I continue to advance my education.”
Pairing up students and mentors to advance education and making use of complementary imaging techniques to enhance energy efficiency—just two of the positive outcomes of this successful collaboration.
“By bringing together multiple complementary techniques to illuminate the same process we’re going to understand how nanomaterials work,” Frenkel said. “Ultimately, this research will create a better way of using, storing, and converting energy.”
The CFN and NSLS facilities at Brookhaven Lab are supported by the Department of Energy’s Office of Science. The collaborative work of Frenkel and Stach is funded by the Office of Science and Brookhaven’s Laboratory Directed Research and Development program.
The Center for Functional Nanomaterials is one of five DOE Nanoscale Science Research Centers (NSRCs), national user facilities for interdisciplinary research at the nanoscale, supported by the DOE Office of Science. Together the NSRCs comprise a suite of complementary facilities that provide researchers with state-of-the-art capabilities to fabricate, process, characterize and model nanoscale materials, and constitute the largest infrastructure investment of the National Nanotechnology Initiative. The NSRCs are located at DOE’s Argonne, Brookhaven, Lawrence Berkeley, Oak Ridge and Sandia and Los Alamos National Laboratories. For more information about the DOE NSRCs, please visit http://science.energy.gov.
The National Synchrotron Light Source (NSLS) provides intense beams of infrared, ultraviolet, and x-ray light for basic and applied research in physics, chemistry, medicine, geophysics, and environmental and materials sciences. Supported by the Office of Basic Energy Sciences within the U.S. Department of Energy, the NSLS is one of the world’s most widely used scientific facilities. For more information, visit http://www.nsls.bnl.gov.
DOE’s Office of Science is the single largest supporter of basic research in the physical sciences in the United States, and is working to address some of the most pressing challenges of our time. For more information, please visit science.energy.gov
This story incorporates content from a piece by Perel Skier on the Yeshiva University news blog.
14 Nov 2013
|(Nanowerk News) Researchers have created tiny protein tubes named after the Roman god Janus which may offer a new way to accurately channel drugs into the body’s cells.|
|Using a process which they liken to molecular Lego, scientists from the University of Warwick and the University of Sydney have created what they have named ‘Janus nanotubes’ – very small tubes with two distinct faces. The study is published in the journal Nature Communications (“Janus cyclic peptide–polymer nanotubes”).|
|They are named after the Roman god Janus who is usually depicted as having two faces, since he looks to the future and the past.|
|The Janus nanotubes have a tubular structure based on the stacking of cyclic peptides, which provide a tube with a channel of around 1nm – the right size to allow small molecules and ions to pass through.|
|Attached to each of the cyclic peptides are two different types of polymers, which tend to de-mix and form a shell for the tube with two faces – hence the name Janus nanotubes.|
|The faces provide two remarkable properties – in the solid state, they could be used to make solid state membranes which can act as molecular ‘sieves’ to separate liquids and gases one molecule at a time. This property is promising for applications such as water purification, water desalination and gas storage.|
|In a solution, they assemble in lipids bilayers, the structure that forms the membrane of cells, and they organise themselves to form pores which allow the passage of molecules of precise sizes. In this state they could be used for the development of new drug systems, by controlling the transport of small molecules or ions inside cells.|
|Sebastien Perrier of the University of Warwick said: “There is an extraordinary amount of activity inside the body to move the right chemicals in the right amounts both into and out of cells.|
|“Much of this work is done by channel proteins, for example in our nervous system where they modulate electrical signals by gating the flow of ions across the cell membrane.|
|“As ion channels are a key component of a wide variety of biological process, for example in cardiac, skeletal and muscle contraction, T-cell activation and pancreatic beta-cell insulin release, they are a frequent target in the search for new drugs.|
|“Our work has created a new type of material – nanotubes – which can be used to replace these channel processes and can be controlled with a much higher level of accuracy than natural channel proteins.|
|“Through a process of molecular engineering – a bit like molecular Lego – we have assembled the nanotubes from two types of building blocks – cyclic peptides and polymers.|
|“Janus nanotubes are a versatile platform for the design of exciting materials which have a wide range of application, from membranes – for instance for the purification of water, to therapeutic uses, for the development of new drug systems.”|
|Source: University of Warwick|
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|(Nanowerk News) Advanced plasma-based etching is a key enabler of Moore’s Law that observes that the number of transistors on integrated circuits doubles nearly every two years. It is the plasma’s ability to reproduce fine patterns on silicon that makes this scaling possible and has made plasma sources ubiquitous in microchip manufacturing.|
|A groundbreaking fabrication technique, based on what is called a DC-augmented capacitively coupled plasma source, affords chip makers unprecedented control of the plasma. This process enables DC-electrode borne electron beams to reach and harden the surface of the mask that is used for printing the microchip circuits. More importantly, the presence of the beam creates a population of suprathermal electrons in the plasma, producing the plasma chemistry that is necessary to protect the mask. The energy of these electrons is greater than simple thermal heating could produce—hence the name “suprathermal.” But how the beam electrons transform themselves into this suprathermal population has been a puzzle.|
|A plasma wave can give rise to a population of suprathermal electrons. (Credit: I.D. Kaganovich and D. Sydorenko)|
|Now a computer simulation developed at the U.S. Department of Energy’s Princeton|
|Plasma Physics Laboratory in collaboration with the University of Alberta has shed light on this transformation. The simulation reveals that the initial DC-electrode borne beam generates intense plasma waves that move through the plasma like ripples in water. And it is this beam-plasma instability that leads to the generation of the crucial suprathermal electrons.|
|Understanding the role these instabilities play provides a first step toward still-greater control of the plasma-surface interactions, and toward further increasing the number of transistors on integrated circuits. Insights from both numerical simulations and experiments related to beam-plasma instabilities thus portend the development of new plasma sources and the increasingly advanced chips that they fabricate.|
|55th Annual Meeting of the APS Division of Plasma Physics|
|TO6.00005 Collisionless acceleration of plasma electrons by intense electron beam|
|Session: Low Temperature Plasma Science, Engineering and Technology|
|9:30 AM–11:06 AM, Thursday, November 14, 2013|
|Source: American Physical Society|