'Super sand' for better purification of drinking water

'Super sand' for better purification of drinking water

  8:57:00 PM    Science Lover

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Scientists have developed a way to transform ordinary sand — a mainstay filter material used to purify drinking water throughout the world — into a "super sand" with five times the filtering capacity of regular sand. The new material could be a low-cost boon for developing countries, where more than a billion people lack clean drinking water, according to the report in the ACS journal Applied Materials & Interfaces.

Mainak Majumder and colleagues note that sand has been used to purify water for more than 6,000 years, and sand or gravel water filtration is endorsed by the World Health Organization. Their studies of a nanomaterial called graphite oxide (GO) suggest that it could be used to improve sand filtration in a cost-effective way, they write.

The researchers used a simple method to coat sand grains with graphite oxide, creating a super sand that successfully removed mercury and a dye molecule from water. In the mercury test, ordinary sand was saturated within 10 minutes of filtration, while the super sand absorbed the heavy metal for more than 50 minutes, the scientists discovered. Its filtration "performance is comparable to some commercially available activated carbon," the scientists said. "We are currently investigating strategies that will enable us to assemble functionalized GO particles on the sand grains to further enhance contaminant removal efficiencies," they write.

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Nano-engineered cotton promises to wipe out water bugs

Nano-engineered cotton promises to wipe out water bugs

  2:02:00 AM    Science Lover

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COTTON impregnated with silver nanowires and carbon nanotubes (CNTs) could provide a cheap and effective method of purifying water in remote locations.

A new filter needs only gravity and a weak electric current to produce its sterilising effect, making it suitable for a portable water-treatment device.

The fabric is easy to produce, says lead researcher Yi Cui at Stanford University in California. Cui's team simply dip a piece of cotton into a solution of CNTs and then pipette droplets containing silver nanowires onto the cotton.

Prepare to die, E. coli (Image: Linda Stannard/UCT/SPL)

Analysing the fabric with a scanning electron microscope reveals that the CNTs stick to the individual cotton fibres, while the slightly larger silver nanowires form a mesh between the fibres. The nanoparticles enable the fabric to conduct electricity, so a weak electric current can run across it. This helps kill bacteria by damaging their outer membranes, while the silver nanowires' anti-bacterial properties do the rest.

So when Cui and his colleagues poured water contaminated with the bacterium Escherichia coli (pictured) through the silver-coated, electrically-conducting fabric, they found it killed 89 per cent of the bacteria. By conducting three successive runs through the fabric, they were able to kill over 98 per cent - enough to make the water safe to drink (Nano Letters, DOI: 10.1021/nl101944e).

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Dry Water Could Make a Big Splash Commercially, Help Fight Global Warming

Dry Water Could Make a Big Splash Commercially, Help Fight Global Warming

  12:40:00 AM    Science Lover

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An unusual substance known as "dry water," which resembles powdered sugar, could provide a new way to absorb and store carbon dioxide, the major greenhouse gas that contributes to global warming, scientists reported at the 240th National Meeting of the American Chemical Society.

Powdered material called "dry water" could provide a new way to store carbon dioxide in an effort to fight global warming. (Credit: Ben Carter)

The powder shows bright promise for a number of other uses, they said. It may, for instance, be a greener, more energy-efficient way of jumpstarting the chemical reactions used to make hundreds of consumer products. Dry water also could provide a safer way to store and transport potentially harmful industrial materials.

"There's nothing else quite like it," said Ben Carter, Ph.D., researcher for study leader Professor Andrew Cooper. "Hopefully, we may see 'dry water' making waves in the future."

Carter explained that the substance became known as "dry water" because it consists of 95 percent water and yet is a dry powder. Each powder particle contains a water droplet surrounded by modified silica, the stuff that makes up ordinary beach sand. The silica coating prevents the water droplets from combining and turning back into a liquid. The result is a fine powder that can slurp up gases, which chemically combine with the water molecules to form what chemists term a hydrate.

Dry water was discovered in 1968 and got attention for its potential use in cosmetics. Scientists at the University of Hull, U.K. rediscovered it in 2006 in order to study its structure, and Cooper's group at the University of Liverpool has since expanded its range of potential applications.

One of the most recent involves using dry water as a storage material for gases, including carbon dioxide. In laboratory-scale research, Cooper and co-workers found that dry water absorbed over three times as much carbon dioxide as ordinary, uncombined water and silica in the same space of time. This ability to absorb large amounts of carbon dioxide gas as a hydrate could make it useful in helping to reduce global warming, the scientists suggested.

Cooper and colleagues demonstrated in previous studies that dry water is also useful for storing methane, a component of natural gas, and may help expand its use as a future energy source. In particular, they hope that engineers can use the powder to collect and transport stranded deposits of natural gas. This also exists on the ocean floor in the form of gas hydrates, a form of frozen methane also known as the "ice that burns." The powder could also provide a safer, more convenient way to store methane fuel for use in vehicles powered by natural gas. "A great deal of work remains to be done before we could reach that stage," Carter added.

In another potential new application, the scientists also showed that dry water is a promising means to speed up catalyzed reactions between hydrogen gas and maleic acid to produce succinic acid, a feedstock or raw material widely used to make drugs, food ingredients, and other consumer products. Manufacturers usually have to stir these substances together to get them to react. By developing dry water particles that contain maleic acid, Cooper and colleagues showed that they could speed up the acid's reaction with hydrogen without any stirring, resulting in a greener, more energy-efficient process.

"If you can remove the need to stir your reactions, then potentially you're making considerable energy savings," Carter said.

Prof. Cooper's team describes an additional new application in which dry water technology shows promise for storing liquids, particularly emulsions. Emulsions are mixtures of two or more unblendable liquids, such as the oil and water mixture in mayonnaise. The scientists showed that they could transform a simple emulsion into a dry powder that is similar to dry water. The resulting powder could make it safer and easier for manufacturers to store and transport potentially harmful liquids.

Carter noted that he and his colleagues are seeking commercial or academic collaboration to further develop the dry water technology. The U.K. Engineering and Physical Sciences Research Council (EPSRC) and the Center for Materials Discovery provided funding and technical support for this study.

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Physicists Hope to Unlock Secrets of Life

Physicists Hope to Unlock Secrets of Life

  11:09:00 PM    Science Lover

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The key to life as we know it is water, a tiny molecule with some highly unusual properties, such as the ability to retain large amounts of heat and to lose, instead of gain, density as it solidifies. It behaves so differently from other liquids, in fact, that by some measures it shouldn't even exist. Now scientists have made a batch of new discoveries about the ubiquitous liquid, suggesting that an individual water molecule's interactions with its neighbors could someday be manipulated to solve some of the world's thorniest problems -- from agriculture to cancer.

Supercool. As individual water molecules fluctuate, breaking and forming bonds with their nearest neighbors, the result is slightly imperfect tetrahedral structures that are constantly in flux. Research suggests that these fluctuations give rise to some of water's most unusual and life-sustaining features. (Credit: Image courtesy of Rockefeller University)

The work, led by Pradeep Kumar, a fellow at Rockefeller University's Center for Studies in Physics and Biology who looks at the role of water in biology, makes it possible to measure how interaction between water molecules affect any number of properties in a system. It also paves the way for understanding how water can be manipulated to facilitate or prevent substances from dissolving in it, an advance that could impact every corner of society, from reforming agricultural practices to improving chemotherapy drugs whose side effects arise from their solubility or insolubility in water.

Kumar and his colleagues first tracked individual water molecules in a "supercooled" state (water that remains in liquid form even at below freezing temperatures), during which water's many anomalies are enhanced. "When you put water in a freezer, it doesn't freeze instantaneously," says Kumar. "It takes some time. If you have extremely pure water, then you can go down to about 230 Kelvin and still have enough time to measure different physical properties of water including the specific heat in its liquid state." Kumar and his colleagues then used theoretical and computational approaches to simulate the activity of these water molecules and measure their interactions with neighbors.

In the liquid state, every water molecule fleetingly interacts with its four nearest neighbors, forming a tetrahedron, explains Kumar. These tetrahedrons, however, are slightly imperfect and the degree to which they are changes as temperature and pressure change, ultimately affecting which individual water molecules partner up with each other. Kumar found that it is the fluctuations in the degree of tetrahedrality that contribute most to one of water's most notable and valuable features -- its capacity to resist heating or cooling and thereby regulating and maintaining the temperature of biological systems.

The ability to measure water's shifting degrees of tetrahedrality also gives scientists a means of measuring how much order or disorder each water molecule imparts. The better the tetrahedron, the more order it imparts in the system. "What we have done essentially is define the structural entropy of every molecule in our system," says Kumar. "And since water molecules are constantly moving in space and time, this gives you a way to study the transport of entropy associated with local tetrahedrality -- something that has never been done before."

Understanding how individual water molecules maneuver in a system to form fleeting tetrahedral structures and how changing physical conditions such as temperatures and pressures affect the amount of disorder each imparts on that system may help scientists understand why certain substances, like drugs used in chemotherapy, are soluble in water and why some are not.

It could also help understand how this changing network of bonds and ordering of local tetrahedrality between water molecules changes the nature of protein folding and degradation. "Understanding hydrophobicity, and how different conditions change it, is probably one of the most fundamental components in understanding how proteins fold in water and how different biomolecules remain stable in it," says Kumar. "And if we understand this, we will not only have a new way of thinking about physics and biology but also a new way to approach health and disease."

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Lasers Generate Underwater Sound: Potential For Naval And Commercial Underwater Acoustic Applications

Lasers Generate Underwater Sound: Potential For Naval And Commercial Underwater Acoustic Applications

  9:34:00 PM    Science Lover

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Scientists at the Naval Research Laboratory are developing a new technology for use in underwater acoustics. The new technology uses flashes of laser light to remotely create underwater sound. The new acoustic source has the potential to expand and improve both Naval and commercial underwater acoustic applications, including undersea communications, navigation, and acoustic imaging.

Scattered light from a 532 nm laser pulse can be seen as it enters the water in the Salt Water Tank Facility, and ionizes a small volume of water for acoustic generation. Air bubblers and controlled water and air temperatures can create ocean-like conditions in the laboratory. (Credit: Image courtesy of Naval Research Laboratory)

Dr. Ted Jones, a physicist in the Plasma Physics Division, is leading a team of researchers from the Plasma Physics, Acoustics, and Marine Geosciences Divisions in developing this acoustic source.

Efficient conversion of light into sound can be achieved by concentrating the light sufficiently to ionize a small amount of water, which then absorbs laser energy and superheats. The result is a small explosion of steam, which can generate a 220 decibel pulse of sound. Optical properties of water can be manipulated with very intense laser light to act like a focusing lens, allowing nonlinear self-focusing (NSF) to take place.

In addition, the slightly different colors of the laser, which travel at different speeds in water due to group velocity dispersion (GVD), can be arranged so that the pulse also compresses in time as it travels through water, further concentrating the light. By using a combination of GVD and NSF, controlled underwater compression of optical pulses can be attained.

The driving laser pulse has the ability to travel through both air and water, so that a compact laser on either an underwater or airborne platform can be used for remote acoustic generation. Since GVD and NSF effects are much stronger in water than air, a properly tailored laser has the ability to travel many hundreds of meters through air, remaining relatively unchanged, then quickly compress upon entry into the water. Atmospheric laser propagation is useful for applications where airborne lasers produce underwater acoustic signals without any required hardware in the water, such as undersea communications from aircraft.

Also, commercially available, high-repetition-rate pulsed lasers, steered by a rapidly movable mirror, can generate arbitrary arrays of phased acoustic sources. On a compact underwater platform with an acoustic receiver, such a setup can rapidly generate oblique-angle acoustic scattering data, for imaging and identifying underwater objects. This would be a significant addition to traditional direct backscattering acoustic data.

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