Chemists work to desalt the ocean for drinking water, 1 nanoliter at a time


QDOTS imagesCAKXSY1K 8(Nanowerk News) By creating a small electrical field  that removes salts from seawater, chemists at The University of Texas at Austin  and the University of Marburg in Germany have introduced a new method for the  desalination of seawater that consumes less energy and is dramatically simpler  than conventional techniques. The new method requires so little energy that it  can run on a store-bought battery.
The process evades the problems confronting current desalination  methods by eliminating the need for a membrane and by separating salt from water  at a microscale.
The technique, called electrochemically mediated seawater  desalination, was described last week in the journal Angewandte Chemie (“Electrochemically Mediated Seawater  Desalination”). The research team was led by Richard Crooks of The  University of Texas at Austin and Ulrich Tallarek of the University of Marburg.  It’s patent-pending and is in commercial development by startup company Okeanos  Technologies.
Desalination Microchannel
The  left panel shows the salt (which is tagged with a fluorescent tracer) flowing  upward after a voltage is applied by an electrode (the dark rectangle) jutting  into the channel at just the point where it branches. In the right panel no  voltage is being applied. (Image: Kyle Knust)
“The availability of water for drinking and crop irrigation is  one of the most basic requirements for maintaining and improving human health,”  said Crooks, the Robert A. Welch Chair in Chemistry in the College of Natural  Sciences. “Seawater desalination is one way to address this need, but most  current methods for desalinating water rely on expensive and easily contaminated  membranes. The membrane-free method we’ve developed still needs to be refined  and scaled up, but if we can succeed at that, then one day it might be possible  to provide fresh water on a massive scale using a simple, even portable,  system.”
This new method holds particular promise for the water-stressed  areas in which about a third of the planet’s inhabitants live. Many of these  regions have access to abundant seawater but not to the energy infrastructure or  money necessary to desalt water using conventional technology. As a result,  millions of deaths per year in these regions are attributed to water-related  causes.
“People are dying because of a lack of freshwater,” said Tony  Frudakis, founder and CEO of Okeanos Technologies. “And they’ll continue to do  so until there is some kind of breakthrough, and that is what we are hoping our  technology will represent.”
To achieve desalination, the researchers apply a small voltage  (3.0 volts) to a plastic chip filled with seawater. The chip contains a  microchannel with two branches. At the junction of the channel an embedded  electrode neutralizes some of the chloride ions in seawater to create an “ion  depletion zone” that increases the local electric field compared with the rest  of the channel. This change in the electric field is sufficient to redirect  salts into one branch, allowing desalinated water to pass through the other  branch.
“The neutralization reaction occurring at the electrode is key  to removing the salts in seawater,” said Kyle Knust, a graduate student in  Crooks’ lab and first author on the paper.
Like a troll at the foot of the bridge, the ion depletion zone  prevents salt from passing through, resulting in the production of freshwater.
Thus far Crooks and his colleagues have achieved 25 percent  desalination. Although drinking water requires 99 percent desalination, they are  confident that goal can be achieved.
“This was a proof of principle,” said Knust. “We’ve made  comparable performance improvements while developing other applications based on  the formation of an ion depletion zone. That suggests that 99 percent  desalination is not beyond our reach.”
The other major challenge is to scale up the process. Right now  the microchannels, about the size of a human hair, produce about 40 nanoliters  of desalted water per minute. To make this technique practical for individual or  communal use, a device would have to produce liters of water per day. The  authors are confident that this can be achieved as well.
If these engineering challenges are surmounted, they foresee a  future in which the technology is deployed at different scales to meet different  needs.
“You could build a disaster relief array or a municipal-scale  unit,” said Frudakis. “Okeanos has even contemplated building a small system  that would look like a Coke machine and would operate in a standalone fashion to  produce enough water for a small village.”
Source: McGill University

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Integration Of Photonic And Electronic Components


QDOTS imagesCAKXSY1K 8Better integration of photonic and electronic components in nanoscale devices may now become possible, thanks to work by Khuong Phuong Ong and Hong-Son Chu from the A*A*STAR Institute of High Performance Computing and their co-workers in Singapore and the US. From computer simulations, they have identified that the compound BiFeO3 has the potential to be used to efficiently couple light to electrical charges through light-induced electron oscillations known as plasmons. The researchers propose that this coupling could be activated, controlled and switched off, on demand, by applying an electrical field to an active plasmonic device based on this material. If such a device were realized on a very small footprint it would give scientists a versatile tool for connecting components that manipulate light or electric currents.

poles

Thin poles standing in water barely affect waves rolling past them. Similarly, nanostructured devices typically do not interact with light waves

Many devices used in everyday life — whether they be televisions, mobile phones or barcode scanners — are based on the manipulation of electric currents and light. At the micro- and nano-scales, however, it is typically challenging to integrate electronic components with photonic components. At these small dimensions, the wavelengths of light become long relative to the size of the device. Consequently, the light waves are barely detectable by the device, just as passing waves simply roll past thin poles in a water body (see image).

“The fact that, in theory, the properties of BiFeO3 [could] be [so readily controlled] by applying an electric field makes it a promising material for high-performance plasmonic devices,” explains Ong. He says that they expected such favorable properties after they had calculated the behavior of the material. But when they studied the behavior of the proposed BiFeO3-based device, they found that it could outperform devices based on BaTiO3, which is one of the best materials currently used for such applications.

Like BaTiO3, BiFeO3 can be fabricated relatively easily and cheaply. The new material is therefore a particularly promising candidate for device applications. Ong, Chu and their collaborators will now explore that potential. “We will design BiFeO3 nanostructures optimized for applications such as optical devices for data communication, sensing and solar-energy conversion,” says Ong.

According to Ong and Chu, an important step on the path to producing practical devices will be assessing the compatibility of BiFeO3-based structures with standard technologies, which typically use materials known as metal-oxide semiconductors. This future work will involve collaborations with experimental groups at the A*STAR Institute of Materials Research and Engineering and at the National University of Singapore.

 

The A*STAR-affiliated researchers contributing to this research are from the Institute of High Performance

 

Guiding stem cell migration to heal wounds


QDOTS imagesCAKXSY1K 8Healing cells migrate toward injured tissue not unlike how animals carry out their annual migrations – which is to say that it’s all a bit of a mystery. Grantees at UC Davis are working to clear up at least some of the mystery as a first step in learning to how guide stem cells to where they are needed.

 

There’s some evidence that wounds disrupt normal electric currents, and that cells can navigate toward that disruptions. Min Zhao and his colleagues at UC Davis have been studying how the cells detect this current and migrate accordingly. A press release about their work, published in the April 8 issue of Current Biology, quotes Zhao:

“We know that cells can respond to a weak electrical field, but we don’t know how they sense it. If we can understand the process better, we can make wound healing and tissue regeneration more effective.

They went on to give this inspired description of how cells move:

Think of a cell as a blob of fluid and protein gel wrapped in a membrane. Cells crawl along surfaces by sliding and ratcheting protein fibers inside the cell past each other, advancing the leading edge of the cell while withdrawing the trailing edge.

Essentially, all those ratcheting and sliding fibers seem to respond to the electric signal, drawing the cell toward the negative electrode.
In his Basic Biology award, which funded this work, Zhao says he hopes to optimize the type of current needed to direct the migration of stem cells to sites where they are needed. He recently filmed an Elevator Pitch with us, describing how his work could be used to guide stem cells toward a brain region damaged by stroke.

Watch the video on YouTube Here: http://www.youtube.com/watch?v=GwZ_ruVKfGk&feature=share&list=PLIeX9Lq8O-wHxcx3CleSdE5yuqUkm9Ogw

Making Nano-Fibers Affordable


QDOTS imagesCAKXSY1K 8Nanofibers — strands of material only a couple hundred nanometers in diameter — have a huge range of possible applications: scaffolds for bioengineered organs, ultrafine air and water filters, and lightweight Kevlar body armor, to name just a few. But so far, the expense of producing them has consigned them to a few high-end, niche applications.
Luis Velásquez-García, a principal research scientist at MIT’s Microsystems Technology Laboratories, and his group hope to change that. At the International Workshop on Micro and Nanotechnology for Power Generation and Energy Conversion Applications in December, Velásquez-García, his student Philip Ponce de Leon, and Frances Hill, a postdoc in his group, will describe a new system for spinning nanofibers that should offer significant productivity increases while drastically reducing power consumption.
Using manufacturing techniques common in the microchip industry, the MTL researchers built a one-square-centimeter array of conical tips, which they immersed in a fluid containing a dissolved plastic. They then applied a voltage to the array, producing an electrostatic field that is strongest at the tips of the cones. In a technique known as electrospinning, the cones eject the dissolved plastic as a stream that solidifies into a fiber only 220 nanometers across.

In their experiments, the researchers used a five-by-five array of cones, which already yields a sevenfold increase in productivity per square centimeter over even the best existing methods. But, Velásquez-García says, it should be relatively simple to pack more cones onto a chip, boosting productivity even more. Indeed, he says, in prior work on a similar technique called electrospray, his lab was able to cram almost a thousand emitters into a single square centimeter. And multiple arrays could be combined in a panel to further increase yields.

Surfaces, from scratch
Because the new paper was prepared for an energy conference, it focuses on energy applications. But nanofibers could be useful for any device that needs to maximize the ratio of surface area to volume, Velásquez-García says. Capacitors — circuit components that store electricity — are one example, because capacitance scales with surface area. The electrodes used in fuel cells are another, because the greater the electrodes’ surface area, the more efficiently they catalyze the reactions that drive the cell. But almost any chemical process can benefit from increasing catalysts’ surface area, and increasing the surface area of artificial-organ scaffolds gives cells more points at which to adhere.

Watch the Video Here: http://youtu.be/eWGPW1tS38U

Another promising application of nanofibers is in meshes so fine that they allow only nanoscale particles to pass through. The example in the new paper again comes from energy research: the membranes that separate the halves of a fuel cell. But similar meshes could be used to filter water. Such applications, Velásquez-García says, depend crucially on consistency in the fiber diameter, another respect in which the new technique offers advantages over its predecessors.

Existing electrospinning techniques generally rely on tiny nozzles, through which the dissolved polymer is forced. Variations in operating conditions and in the shape of the nozzles can cause large variation in the fiber diameter, and the nozzles’ hydraulics mean that they can’t be packed as tightly together. A few manufacturers have developed fiber-spinning devices that use electrostatic fields, but their emitters are made using much cruder processes than the chip-manufacturing techniques that the MTL researchers exploited. As a consequence, not only are the arrays of tips much less dense, but the devices consume more power.
“The electrostatic field is enhanced if the tip diameter is smaller,” Velásquez-García says. “If you have tips of, say, millimeter diameter, then if you apply enough voltage, you can trigger the ionization of the liquid and spin fibers. But if you can make them sharper, then you need a lot less voltage to achieve the same result.”

Wicked wicker
The use of microfabrication technologies not only allowed the MTL researchers to pack their cones more tightly and sharpen their tips, but it also gave them much more precise control of the structure of the cones’ surfaces. Indeed, the sides of the cones have a nubby texture that helps the cones wick up the fluid in which the polymer is dissolved. In ongoing experiments, the researchers have also covered the cones with what Velásquez-García describes as a “wool” of carbon nanotubes, which should work better with some types of materials.

Indeed, Velásquez-García says, his group’s results depend not only on the design of the emitters themselves, but on a precise balance between the structure of the cones and their textured coating, the strength of the electrostatic field, and the composition of the fluid bath in which the cones are immersed.
“Fabricating exactly identical emitters in parallel with high precision and a lot of throughput — this is their main contribution, in my opinion,” says Antonio Luque Estepa, an associate professor of electrical engineering at the University of Seville who specializes in electrospray deposition and electrospinning.

“Fabricating one is easy. But 100 or 1,000 of them, that’s not so easy. Many times there are problems with interactions between one output and the output next to it.”

The microfabrication technique that Velásquez-García’s group employs, Luque adds, “does not limit the number of outputs that they can integrate on one chip.” Although the extent to which the group can increase emitter density remains to be seen, Luque says, he’s confident that “they can make a tenfold increase over what is available right now.”

The MIT researchers’ work was funded in part by the U.S. Defense Advanced Research Projects Agency.