New nanoparticle technology cuts water use, energy costs

Nuclear and coal power plants are some of the thirstiest machines on earth. The turbines that spin inside of them to generate electricity require tons and tons of steam, and all of that water has to come from somewhere.

Recent studies have estimated that roughly two-fifths of the nation’s freshwater withdrawals and three percent of overall freshwater consumption goes to supplying the steam generators at large power stations in the United States. In order to cut down on the enormous quantities of water required to operate these plants, scientists have begun to look for new technologies that could improve their efficiency and reduce the demand for water.

As part of a larger consortium involving partners from several energy companies, universities, and government agencies, researchers at the U.S. Department of Energy’s Argonne National Laboratory are developing a special class of nanoparticles that partially melt as steam evaporates from a plant’s cooling towers, absorbing a significant percentage of the diffused heat in the system.

In order to operate, electrical plants use a cycle that uses partially condensed high-temperature steam to turn a large turbine.  During generation, a significant quantity of this steam is lost due to evaporation. “In every cycle, there’s a significant amount of water that we can’t recapture,” said Argonne materials scientist Dileep Singh, who is working to develop the specialized nanoparticles.

The nanoparticles are based on what is known as a “core-shell” configuration, in which a solid outer coat protects an inner layer that can melt above a certain temperature. Once dispersed in the plant’s water supply, the nanoparticles are able to absorb heat during the thermal cycle. After partially melting, the particles travel to the cooling tower where they resolidify. The system is closed and designed to ensure against leakage of the plant’s water or steam into the environment.

At the molecular level, Singh and his colleagues are especially concerned with the surface of the nanoparticles, as the chemistry at the boundary between the metal and the water determines how much heat the particles can take up. “We’re experimenting with looking at the bonding between the particles and the water molecules,” he said.

“What we really want to know is how much heat we can pick up given a constant amount of water to cool the system,” he added. “Environmentally responsible energy growth involves worrying about how you manage your water resources.”

The vast quantities of water that are needed to operate these facilities will necessitate the mass production of the nanoparticles once they are commercially developed, a fact that could potentially complicate the research and development process, said Argonne associate division director Thomas Ewing. “As we begin lab testing, we need to keep in mind the costs and issues associated with making this work in a real live power plant,” he said. “There are lots of tradeoffs to take into account.”

According to Ewing, Argonne is working with the Electric Power Research Institute and other partners to move this basic technology quickly through the developmental pipeline. Initial plans call for the demonstration of proof of concept to commence this year and full-scale commercial deployment to begin in four years. “It’s practically unheard of for industry to seek to deploy a new technology so quickly,” Ewing said. “However, water consumption is a major issue that limits the expansion of power. If we want to solve the energy crisis, we’ll have to move boldly.”

 More information: here

Sulfur in every pore: Improved batteries with carbon nanoparticles

From smartphones to e-bikes, the number of mobile electronic devices is steadily growing around the world. As a result, there is an increased need for batteries that are small and light, yet powerful. As the potential for the further improvement of lithium-ion batteries is nearly exhausted, experts are now turning to a new and promising power storage device: lithium-sulfur batteries.

In an important step toward the further development of this type of battery, a team led by Professor Thomas Bein of LMU Munich and Linda Nazar of Waterloo University in Canada has developed porous carbon nanoparticles that utilize sulfur molecules to achieve the greatest possible efficiency.

In prototypes of the lithium-sulfur battery, lithium ions are exchanged between lithium- and sulfur-carbon electrodes. The sulfur plays a special role in this system: Under optimal circumstances, it can absorb two lithium ions per sulfur atom. It is therefore an excellent energy storage material due to its low weight. At the same time, sulfur is a poor conductor, meaning that electrons can only be transported with great difficulty during charging and discharging. To improve this battery's design the scientists at Nanosystems Initiative Munich (NIM) strive to generate sulfur phases with the greatest possible interface area for electron transfer by coupling them with a nanostructured conductive material.

To this end, Thomas Bein and his team at NIM first developed a network of porous carbon nanoparticles. The nanoparticles have 3- to 6-nanometer wide pores, allowing the sulfur to be evenly distributed. In this way, almost all of the sulfur atoms are available to accept lithium ions. At the same time they are also located close to the conductive carbon.

"The sulfur is very accessible electrically in these novel and highly porous carbon nanoparticles and is stabilized so that we can achieve a high initial capacity of 1200 mAh/g and good cycle stability," explains Thomas Bein. "Our results underscore the significance of nano-morphology for the performance of new energy storageconcepts."

The carbon structure also reduces the so-called polysulfide problem. Polysulfides form as intermediate products of the electrochemical processes and can have a negative impact on the charging and discharging of the battery. The carbon network binds the polysulfides, however, until their conversion to the desired dilithium sulfide is achieved. The scientists were also able to coat the carbon material with a thin layer of silicon oxide which protects against polysulfides without reducing conductivity.

Incidentally, the scientists have also set a record with their new material: According to the latest data, their material has the largest internal pore volume (2.32 cm3/g) of all mesoporous carbon nanoparticles, and an extremely large surface area of 2445 m2/g. This corresponds roughly to an object with the volume of a sugar cube and the surface of ten tennis courts. Large surface areas like this might soon be hidden inside our batteries.

More information: "Spherical Ordered Mesoporous Carbon Nanoparticles with Extremely High Porosity for Lithium-Sulfur Batteries". Jörg Schuster, Guang He, Benjamin Mandlmeier, Taeeun Yim, Kyu Tae Lee, Thomas Bein and Linda F. Nazar.Angewandte Chemie, 1 MAR 2012.http://onlinelibrary.wiley.com/doi/10.1002/anie.201107817/abstract

Stable electrodes for improving printed electronics

Imagine owning a television with the thickness and weight of a sheet of paper. It will be possible, someday, thanks to the growing industry of printed electronics. The process, which allows manufacturers to literally print or roll materials onto surfaces to produce an electronically functional device, is already used in organic solar cells and organic light-emitting diodes (OLEDs) that form the displays of cellphones.

Although this emerging technology is expected to grow by tens of billions of dollars over the next 10 years, one challenge is in manufacturing at low cost in ambient conditions. In order to create light or energy by injecting or collecting electrons, printed electronics require conductors, usually calcium, magnesium or lithium, with a low-work function. These metals are chemically very reactive. They oxidize and stop working if exposed to oxygen and moisture. This is why electronics in solar cells and TVs, for example, must be covered with a rigid, thick barrier such as glass or expensive encapsulation layers.

However, in new findings published in the journal Science, Georgia Tech researchers have introduced what appears to be a universal technique to reduce the work function of a conductor. They spread a very thin layer of a polymer, approximately one to 10nanometers thick, on the conductor's surface to create a strong surface dipole. The interaction turns air-stable conductors into efficient, low-work function electrodes.

The commercially available polymers can be easily processed from dilute solutions in solvents such as water and methoxyethanol.

"These polymers are inexpensive, environmentally friendly and compatible with existent roll-to-roll mass production techniques," said Bernard Kippelen, director of Georgia Tech's Center for Organic Photonics and Electronics (COPE). "Replacing the reactive metals with stable conductors, including conducting polymers, completely changes the requirements of how electronics are manufactured and protected. Their use can pave the way for lower cost and more flexible devices."

To illustrate the new method, Kippelen and his peers evaluated the polymers' performance in organic thin-film transistors and OLEDs. They've also built a prototype: the first-ever, completely plastic solar cell.

"The polymer modifier reduces the work function in a wide range of conductors, including silver, gold and aluminum," noted Seth Marder, associate director of COPE and professor in the School of Chemistry and Biochemistry. "The process is also effective in transparent metal-oxides and graphene."

 more information: here

Scientists make nontoxic, bendable nanosheets

Cornell materials scientists have developed an inexpensive, environmentally friendly way of synthesizing oxide crystal sheets, just nanometers thick, which have useful properties for electronics and alternative energy applications.

The work, led by Richard Robinson, assistant professor of materials science and engineering, is featured on the cover of the April 7 Journal of Materials Chemistry (Vol. 22, No. 13).

The millimeter-length, 20 nanometer-thick sodium-cobalt oxide crystals were derived through a novel method that combined a traditional sol-gel synthesis with an electric field-induced kinetic de-mixing step. It was this second step that led to the breakthrough of a bottom-up synthesis method through which tens of thousands of nanosheets self-assemble into a pellet.

The material has fascinating properties, Robinson said, including high thermoelectric power, high electrical conductivity, superconductivity and potential as a cathode material in sodium ion batteries.

Usually oxide materials, like a ceramic coffee mug, aren't electrically conductive; they're insulating, Robinson said. Since the material is a conductive oxide, it can be used in thermoelectric devices to convert waste heat into power. Now that the researchers have made nanosheets, they expect the material's thermoelectric efficiency to improve, enabling the creation of more efficient alternative energy thermoelectric devices.

The nanosheets also show the ability to bend, sometimes up to 180 degrees, Robinson added. This is unusual for ceramics, which are normally brittle.

The material is based on common, abundant elements (sodium, cobalt and oxygen), without toxic elements, such as tellurium, that are normally used in thermoelectric devices.

The paper's co-authors are graduate students Mahmut Aksit and David Toledo. The work was supported by the National Science Foundation and the U.S. Department of Energy, through the Energy Materials Center at Cornell (EMC2).

More info: http://phys.org/news/2012-04-scientists-nontoxic-bendable-nanosheets.html

New design for nanoparticles that absorb low-energy light, emit high-energy light may find use in biological imaging

The light that a luminescent particle emits is usually less energetic than the light that it absorbs. Some applications require the emitted light to be more energetic, but this so-called upconversion process has been observed in only a small handful of materials. Xiaogang Liu at the A*STAR Institute of Materials Research and Engineering and co-workers have now succeeded in expanding the list of upconversion materials, easing the path to new applications.

Traditional upconversion particles are distinguished by their evenly-spaced or ‘ladder-like’ energy levels which their internal electrons can take on. The even spacings allow an electron to be promoted up in energy many times consecutively, by absorbing many photons of the same color. When an electron that has been promoted to a high energy finally relaxes back to the lowest-energy state, it emits a photon which is more energetic than the photons that excited it to begin with.

Nanoparticles doped with elements from the lanthanide group of the periodic table are capable of upconversion, and are useful for biological imaging because their high-energy emission can be clearly distinguished from background noise. However, only three elements from the lanthanide series are efficient at upconversion: erbium, thulium, and holmium. This list is so short because of the simultaneous requirements that an upconversion particle exhibit a ladder-like electronic energy structure, and also efficient emission.

Liu and colleagues solved this problem by using different lanthanides to perform different stages of the upconversion process. Sensitizer elements absorb incidentlight, and transfer the absorbed energy to nearby accumulators, whose electrons rise to high energy levels. Then, the energy stored in accumulators transfers by hopping through many migrators, until an activator is reached. Finally, the activator releases a high-energy photon.

By assigning different elements to each of these four functions, the researchers were able to ease the requirements on any individual element. In addition, unwanted interactions among different elements were avoided by separating them spatially inside a single spherical nanoparticle that has sensitizers and accumulators in the core, activators in the shell and migrators in both the core and the shell.

This design allowed Liu and his team to observe a spectrum of colors from the upconverted emission of europium, terbium, dysprosium and samarium (see image). The same approach may also allow other elements to emit efficiently. “Our results may lead to advances in ultrasensitive biodetection,” says Liu, “and should inspire more researchers to work in this field.”

More information:  Wang, F. et al. Tuning upconversion through energy migration in core–shell nanoparticles. Nature Materials 10, 968–973 (2011). http://www.nature.com/nmat/journal/v10/n12/full/nmat3149.html

Imaging complex domain wall structures in magnetic nanostripes

Researchers from the NIST Center for Nanoscale Science and Technology and Massachusetts Institute of Technology have used the scanning electron microscopy with polarization analysis (SEMPA) technique to provide the first direct images of the magnetic structure of highly twisted domain walls in patterned thin film magnetic nanowires.

This imaging method allows these complex and delicate structures to be easily compared to magnetic simulations, a useful step for developing technology that uses domain walls in nanowires for high density data storage and for field or current driven magnetic logic.

A typical domain wall separates two opposite regions of magnetization, making it a “180° wall”. The researchers showed that several 180° walls could be injected into a nanowire, where they either annihilated each other or they combined to form complex walls in which the magnetization rotated by up to 540°. The 360° walls were of particular interest, since their magnetic behavior is dramatically different from the 180° walls currently used in prototype memory and logic devices.

The researchers believe that, in addition to providing information about how 180° walls interact in domain wall-based nanowire memories, this work may lead to new magneto-electronic applications using 360° domain walls, such as manipulating bits using highly localized magnetic fields in magnetic logic circuits

For more info: here

New microscope captures nanoscale structures in dazzling 3D

A new x-ray microscope probes the inner intricacies of materials smaller than human cells and creates unparalleled high-resolution 3D images. By integrating unique automatic calibrations, scientists at the U.S. Department of Energy’s Brookhaven National Laboratory are able to capture and combine thousands of images with greater speed and precision than any other microscope. The direct observation of structures spanning 25 nanometers will offer fundamental advances in many fields, including energy research, environmental sciences, biology, and national defense.

This innovative full field transmission x-ray microscope (TXM), funded by the American Reinvestment and Recovery Act, was developed and commissioned at Brookhaven Lab’s National Synchrotron Light Source (NSLS), which provides the x-ray source needed to capture images on the nanoscale. A new paper published in the April 2012 Applied Physics Letters details the experimental success of a breakthrough system that rapidly combines 2D images taken from every angle to form digital 3D constructs.

“We can actually see the internal 3D structure of materials at the nanoscale,” said Brookhaven physicist Jun Wang, lead author of the paper and head of the team that first proposed this TXM. “The device works beautifully, and it overcomes several major obstacles for x-ray microscopes. We’re excited to see the way this technology will push research.”

Wang’s team examined, for example, a 20-micrometer electrode from a lithium-ion battery – as thin around as a human hair. The internal interaction of pores and particles determines the energy performance of the battery, and examining that activity requires precise knowledge of the nanoscale structure.

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This 3D reconstruction of a lithium-ion battery electrode, composed of 1,441 individual images captured and aligned by the TXM, reveals nano-scale structural details to help guide future energy research.

 more information: here

IBM demonstrates graphene devices for terahertz waves

Graphene has been courted as the miracle material of the future, since different formulations have been fabricated into conductors, semiconductors and insulators. Now IBM has added photonic to the list by demonstrating a graphene/insulator superlattice that achieves a terahertz frequency notch filter and a linear polarizer, devices which could be useful in future mid- and far-infrared photonic devices, including detectors, modulators and three-dimensional metamaterials (see paper inNature Nanotechnology: "Tunable infrared plasmonic devices using graphene/insulator stacks"

"In addition to its good electrical properties, graphene also has exceptional optical properties. In particular, it absorbs light from the far-infrared to to the ultra-violet," said IBM Fellow Phaedon Avouris. "The terahertz range was of particular interest to IBM, because these frequencies can penetrate paper, wood and other solid objects for security applications. Unfortunately, today there are very few ways of manipulating terahertz waves such as polarizing and filtering it, but because graphene operates well at terahertz frequencies we have concentrating on creating these types of devices."

Teraherz frequency oscillations can be carried in graphene by plasmons—the collective oscillation of carriers—to enable low-loss tunable filters. But in single-layer graphene, the carrier concentration and resonant frequency was too weak for photonics applications, according to IBM. However, by going to a multi-layer graphene/instulator superlattice, transparent devices can be patterned into photonic-like crystals that distribute the carriers among the layers effectively enhancing both the carrier density and the resonant frequency


More information here

'Super-nano' plastic fibres touted for next-generation IT

Materials scientists in France said on Sunday they had made highly-conductive plastic wires on the nanoscale, an invention with potential for mobile devices, computing and solar energy.

Just a few billionths of a metre across, the fibres are light, inexpensive, flexible and easy to handle, in contrast to carbon nanotubes, the team said in the journal Nature Chemistry.

The wires are derivatives of man-made molecules called triarylamines that have been used for decades in photocopiers.

In their study, the scientists say they were surprised to find that the wires "self-assemble" spontaneously in response to a flash of light, and are nearly as conductive as copper.

In a bench-test experiment, the tiny materials formed a bridge between two electrodes that were spaced 100 nanometres (100 billionths of a metre) apart.

"The researchers now hope to demonstrate that their fibres can be used industrially in miniaturised electronic devices such as flexible screens, solar cells, transistors (and) printed nanocircuits," the National Centre for Scientific Research (CNRS) said in a press release.

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This picture taken in 2011 in Les Mees, southern France shows solar panels. Materials scientists in France said on Sunday they had made highly-conductive plastic wires on the nanoscale, an invention with potential for mobile devices, computing and solar energy

 more info: here

Quantum dot LEDs get brighter, more efficient

 While quantum dot-based light-emitting diodes (QLEDs) are not made of organic materials, they share many of the same advantages as organic LEDs (OLEDs). For instance, both QLEDs and OLEDs outshine semiconductor-based LEDs in terms of their greater flexibility, better color quality, and potential for lower cost since they can be fabricated using a simple process on a large-area substrate. But ever since the first QLEDs were demonstrated in the mid-'90s, about a decade after OLEDs, their performance has lagged behind OLEDs despite ongoing improvements. Now in a new study, a team of researchers from South Korea has designed and demonstrated QLEDs with an improved efficiency and unprecedented brightness that matches the brightness of today's best fluorescent OLEDs.

The key to improving the brightness and efficiency of the QLEDs is improving the injection of current-carrying electrons and holes into the quantum dots. The more efficiently the electrodes can inject electrons and holes into the quantum dots, the more efficiently the device can emit light. Usually, the anode is made of indium tin oxide, whose transparency allows light to escape. But here, the researchers inverted the device by making the indium tin oxide the cathode with the help of zinc oxide nanoparticles as an electron transport layer, which performed charge carrier injection much more efficiently than before.

“The most important cause of the low performance of QLEDs is the poor injection of holes into the quantum dots (QDs) from the anode and neighboring hole transport layer due to a huge potential energy barrier,” Changhee Lee told Phys.org. “Because of that, the electron-hole balance is not achieved, resulting in low quantum efficiency and low maximum brightness. Furthermore, the excess electrons or holes, which do not recombine in the QD layer and enter the neighboring organic hole-transport orelectron-transport layers (HTL or ETL), can cause leakage current and device degradation, resulting in poor efficiency and stability. Therefore, good carrier injection is a key factor for realizing high-performance QLEDs.”

For more information : http://phys.org/news/2012-04-quantum-dot-brighter-efficient.html