Novel device removes heavy metals from water

Ridding water of trace metals "is really hard to do," said Joseph Calo, professor emeritus of engineering who maintains an active laboratory at Brown. He noted the cost, inefficiency, and time needed for such efforts. "It's like trying to put the genie back in the bottle."

That may be changing. Calo and other engineers at Brown describe a novel method that collates trace heavy metals in water by increasing their concentration so that a proven metal-removal technique can take over. In a series of experiments, the engineers report the method, called the cyclic electrowinning/precipitation (CEP) system, removes up to 99 percent of copper, cadmium, and nickel, returning the contaminated water to federally accepted standards of cleanliness. The automated CEP system is scalable as well, Calo said, so it has viable commercial potential, especially in the environmental remediation and metal recovery fields. The system's mechanics and results are described in a paper published in the Chemical Engineering Journal.

A proven technique for removing heavy metals from water is through the reduction of heavy metal ions from an electrolyte. While the technique has various names, such as electrowinning, electrolytic removal/recovery or electroextraction, it all works the same way, by using an electrical current to transform positively charged metal ions (cations) into a stable, solid state where they can be easily separated from the water and removed. The main drawback to this technique is that there must be a high-enough concentration of metal cations in the water for it to be effective; if the cation concentration is too low — roughly less than 100 parts per million — the current efficiency becomes too low and the current acts on more than the heavy metal ions.

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Brown engineers have devised an automated system that combines chemical precipitation with electrolytic techniques in a cyclic fashion to remove mixtures of trace heavy metals from contaminated water. Credit: Joseph Calo lab, Brown University

Another way to remove metals is through simple chemistry. The technique involves using hydroxides and sulfides to precipitate the metal ions from the water, so they form solids. The solids, however, constitute a toxic sludge, and there is no good way to deal with it. Landfills generally won't take it, and letting it sit in settling ponds is toxic and environmentally unsound. "Nobody wants it, because it's a huge liability," Calo said.

The dilemma, then, is how to remove the metals efficiently without creating an unhealthy byproduct. Calo and his co-authors, postdoctoral researcher Pengpeng Grimshaw and George Hradil, who earned his doctorate at Brown and is now an adjunct professor, combined the two techniques to form a closed-loop system. "We said, 'Let's use the attractive features of both methods by combining them in a cyclic process,'" Calo said.

It took a few years to build and develop the system. In the paper, the authors describe how it works. The CEP system involves two main units, one to concentrate the cations and another to turn them into stable, solid-state metals and remove them. In the first stage, the metal-laden water is fed into a tank in which an acid (sulfuric acid) or base (sodium hydroxide) is added to change the water's pH, effectively separating the water molecules from the metal precipitate, which settles at the bottom. The "clear" water is siphoned off, and more contaminated water is brought in. The pH swing is applied again, first redissolving the precipitate and then reprecipitating all the metal, increasing the metal concentration each time. This process is repeated until the concentration of the metal cations in the solution has reached a point at which electrowinning can be efficiently employed.

When that point is reached, the solution is sent to a second device, called a spouted particulate electrode (SPE). This is where the electrowinning takes place, and the metal cations are chemically changed to stable metal solids so they can be easily removed. The engineers used an SPE developed by Hradil, a senior research engineer at Technic Inc., located in Cranston, R.I. The cleaner water is returned to the precipitation tank, where metal ions can be precipitated once again. Further cleaned, the supernatant water is sent to another reservoir, where additional processes may be employed to further lower the metal ion concentration levels. These processes can be repeated in an automated, cyclic fashion as many times as necessary to achieve the desired performance, such as to federal drinking water standards.

In experiments, the engineers tested the CEP system with cadmium, copper, and nickel, individually and with water containing all three metals. The results showed cadmium, copper, and nickel were lowered to 1.50, 0.23 and 0.37 parts per million (ppm), respectively — near or below maximum contaminant levels established by the Environmental Protection Agency. The sludge is continuously formed and redissolved within the system so that none is left as an environmental contaminant.

"This approach produces very large volume reductions from the original contaminated water by electrochemical reduction of the ions to zero-valent metal on the surfaces of the cathodic particles," the authors write. "For an initial 10 ppm ion concentration of the metals considered, the volume reduction is on the order of 106."

Calo said the approach can be used for other heavy metals, such as lead, mercury, and tin. The researchers are currently testing the system with samples contaminated with heavy metals and other substances, such as sediment, to confirm its operation.

Provided by Brown University (news : web)

Implanted biofuel cell converts bug's chemistry into electricity: Scientists take step toward cyborgs

The finding is yet another in a growing list from universities across the country that could bring the creation of insect cyborgs – touted as possible first responders to super spies – out of science fiction and into reality. In this case, the power supply, while small, doesn't rely on movement, light or batteries, just normal feeding.

The work is published in the online Journal of the American Chemical Society.

"It is virtually impossible to start from scratch and make something that works like an insect," said Daniel Scherson, chemistry professor at Case Western Reserve and senior author of the paper.

"Using an insect is likely to prove far easier," Scherson said. "For that, you need electrical energy to power sensors or to excite the neurons to make the insect do as you want, by generating enough power out of the insect itself."

Scherson teamed with graduate student Michelle Rasmussen, Biology Professor Roy E. Ritzmann, Chemistry Professor Irene Lee and Biology Research Assistant Alan J. Pollack to develop an implantable biofuel cell to provide usable power.

The key to converting the chemical energy is using enzymes in series at the anode.

The first enzyme breaks the sugar, trehalose, which a cockroach constantly produces from its food, into two simpler sugars, called monosaccharides. The second enzyme oxidizes the monosaccharides, releasing electrons.

The current flows as electrons are drawn to the cathode, where oxygen from air takes up the electrons and is reduced to water.

After testing the system using trehalose solutions, prototype electrodes were inserted in a blood sinus in the abdomen of a female cockroach, away from critical internal organs.

"Insects have an open circulatory system so the blood is not under much pressure," Ritzmann explained. "So, unlike say a vertebrate, where if you pushed a probe into a vein or worse an artery (which is very high pressure) blood does not come out at any pressure. So, basically, this is really pretty benign. In fact, it is not unusual for the insect to right itself and walk or run away afterward."

The researchers found the cockroaches suffered no long-term damage, which bodes well for long-term use.

To determine the output of the fuel cell, the group used an instrument called a potentiostat. Maximum power density reached nearly 100 microwatts per square centimeter at 0.2 volts. Maximum current density was about 450 microamps per square centimeter.

The study was five years in the making. Progress stalled for nearly a year due to difficulties with trehalase – the first enzyme used in the series.

Lee suggested they have the trehalase gene chemically synthesized to generate an expression plasmid, which is a DNA molecule separate from chromosomal DNA, to allow the production of large quantities of purified enzyme from Escherichia coli. "Michelle then began collecting enzyme that proved to have much higher specific activities than those obtained from commercial sources," Lee said. "The new enzyme led to success."

The researchers are now taking several steps to move the technology forward: miniaturizing the fuel cell so that it can be fully implanted and allow an insect to run or fly normally; investigating materials that may last long inside of an insect, working with other researchers to build a signal transmitter that can run on little energy; adding a lightweight rechargeable battery.

"It's possible the system could be used intermittently," Scherson said. "An insect equipped with a sensor could measure the amount of noxious gas in a room, broadcast the finding, shut down and recharge for an hour, then take a new measurement and broadcast again."

Provided by Case Western Reserve University (news : web)

Mock atoms prove attractive: Researchers added first pseudo atoms to electronegativity scale

Electron attraction and repulsion determine how atoms and pseudo-atoms behave in different environments. This study provides scientists with the information they need to better predict, manipulate and control those behaviors, whether in batteries for solar farms or catalysts for bio-fuel production.

This study began when Alexander Whiteside, a student at Heriot-Watt University, came to PNNL as part of the 2008 Summer Research Institute for Interfacial and Condensed Phase Physics. During that summer visit, Whiteside, his advisor Maciej Gutowski, and Laboratory Fellow Sotiris Xantheas started to determine the electronegativity of the ammonium radical.

The team calculated the electronic structure of the neutral ammonium molecule, NH4, and its positive and negative ions. Next, they computed the properties of ammonium complexes, specifically combining ammonium with astatine or selected borohydrides; the latter are promising materials for hydrogen storage.

"These results clarified the properties of NH4 and placed it in the proper scale compared to the alkali metals," said Xantheas. "In comparison with alkali atoms, ammonium's electronegativity punches above its effective cationic radius. Nobody had really put it into the scale yet. This study did just that."

The results graced the cover of Chemistry: A European Journal and were highlighted in the Royal Society of Chemistry's Chemistry World.

"Past generations of physical and theoretical chemists were intrigued by the properties ammonium. Alex was standing on the shoulders of giants—Berzelius, Pauling, Mulliken, Herzberg—whose pictures are highlighted in the cover of the journal, while Sotiris and I helped him to keep his balance," joked Gutowski.

"This work opens up the opportunity to developing a comprehensive view on other pseudo-alkali metal species, pseudo-halogens and other pseudo-atoms" says Alexander Boldyrev of Utah State University.

Indeed, the team is expanding their study to the properties of the nearly ubiquitous hydronium and methyl groups, which contain a single oxygen or carbon atom and three hydrogen atoms. In addition, they are examining cyanide, a carbon and nitrogen atom combination that could provide new insights into that pseudo-atom's behavior.

More information: Whiteside A, SS Xantheas, and M Gutowski. 2011. "Is Electronegativity a Useful Descriptor for the Pseudo-Alkali Metal NH4?" Chemistry: A European Journal 17:13197-13205. DOI:10.1002/chem.201101949

Provided by Pacific Northwest National Laboratory (news : web)

New device creates lipid spheres that mimic cell membranes

 Opening up a new door in synthetic biology, a team of researchers has developed a microfluidic device that produces a continuous supply of tiny lipid spheres that are similar in many ways to a cell's outer membrane. "Cells are essentially small, complex bioreactors enclosed by phospholipid membranes," said Abraham Lee from the University of California, Irvine.

"Effectively producing vesicles with lipid membranes that mimic those of natural cells is a valuable tool for fundamental biology research, and it's also an important first step in the hoped-for production of an artificial cell." The researchers have taken an important step in advancing this field by developing a single system that quickly and efficiently performs all the necessary steps to create stable lipid vesicles. Current multistep production methods create vesicles that have inconsistent sizes and layers and short usable lifespans, and they are often contaminated with solvents used in their production.

A paper accepted for publication in the AIP's journal Biomicrofluidics reports that the new microfluidic design overcomes these previous hurdles by generating and manipulating precisely sized droplets of water in an oil environment. This produces an oil-and-water membrane that serves as a scaffold around which lipids molecules assemble. As the membrane dissolves over time, the accumulated lipids form a stable, uniform vesicle that shares many of a natural cell membrane's chemical and physical attributes.

Article: "Stable, Biocompatible Lipid Vesicle Generation by Solvent Extraction-based Droplet Microfluidics" is accepted for publication in the journal Biomicrofluidics.

Authors: Shai-Yen The, Ruba Khnouf, Hugh Fan, Abraham Lee

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The next big step toward atom-specific dynamical chemistry

“Chemistry is inherently dynamical,” he answers. “That means, to make inroads in understanding – and ultimately control – we have to understand how atoms combine to form molecules; how electrons and nuclei couple; how molecules interact, react, and transform; how electrical charges flow; and how different forms of energy move within a molecule or across molecular boundaries.” The list ends with a final and most important question: “How do all these things behave in a correlated way, ‘dynamically’ in time and space, both at the electron and atomic levels?”

Making the most of spectroscopy

Belkacem’s research focuses on creating better ways to track the evolution of energy and charge on the molecular level. For this purpose, one of the sharpest tools in his chemist’s kit goes by the jawbreaking name “nonlinear multidimensional spectroscopy.”

For an outstanding example of the vital questions nonlinear multidimensional electronic spectroscopy can answer, Belkacem points to the work of Graham Fleming, founder of Berkeley Lab’s Physical Biosciences Division. Fleming has tracked energy flow in photosynthesis, demonstrating the electronic coherence among structures in the photosynthetic reaction centers that transform sunlight energy into chemical energy.

“That was done with visible light,” Belkacem says. “We want to do this same kind of chemistry with x-rays.” That’s because understanding photosynthesis and other complex systems means learning how electronic charge is transferred among specific atomic sites, in particular by grasping how valence states are correlated.

Valence electrons – the electrons in the outermost orbitals of atoms and molecules – determine chemical bonding, electrical conductivity, and a host of other properties. But soft x-rays and energetic ultraviolet light can probe the core electrons of atoms, which uniquely identify atomic species in a way that valence electrons can’t.

The most demanding and informative experiments of this kind – which would tackle the compound task of identifying atoms and tracking their correlated valence states quickly and efficiently, over a broad range of materials and processes – require facilities that don’t exist yet. In a research project supported by Berkeley Lab’s Laboratory Directed Research and Development program, Belkacem is using powerful laboratory-scale lasers to test whether multidimensional nonlinear x-ray spectroscopy is practical for the light sources of the future – and just what combination of beam characteristics are needed to define them.

Going where only x-rays can reach

In nonlinear multidimensional spectroscopy, spectroscopy means mapping how a system behaves by seeing how it emits or absorbs different frequencies of light; nonlinear means that the light that goes in isn’t precisely proportional to the light that comes out. It’s not a single overall effect that’s being measured, but individual contributions from different components of the system – different kinds of atoms, say, or different spatial locations.

For pump-probe spectroscopy, the Advanced Light Source (top) and other synchrotron sources boast very high repetition rates but relatively low luminosities, while free-electron lasers are bright but slow. Ali Belkacem and his colleagues are using table-top lasers (bottom) to determine the essential capabilities a new generation of fast, powerful, and highly efficient light source must offer.

Nonlinear and multidimensional spectroscopy results when a light-field perturbs a molecule so that subsequent light-fields see changes in the molecular states. For this kind of spectroscopy, it’s important that the different light pulses interact with the molecular states over very short time periods, in such a way that the information imparted by the first light pulse doesn’t get lost or dissipated.

Synchrotron light sources like Berkeley Lab’s Advanced Light Source can produce coherent (laser-like) light in the desired soft x-ray region, but today’s light sources can’t achieve the enormous peak photon flux – roughly speaking, the peak brightness – needed to realize the full potential of nonlinear multidimensional spectroscopy. For now, such capabilities are available only from ultrafast laser sources operating in the visible and infrared regions.

The emergence of x-ray lasers holds tremendous promise for this field, but the first generation of free-electron lasers (FELs) to come online in Europe and the U.S. does not yet provide the right combination of average power, very short pulses, multi-color pulses (more than one wavelength of light), and very high repetition rates – a hundred thousand pulses a second or more – essential to the future light sources that will operate in the soft-x-ray and extreme-ultraviolet regime.

At present, Belkacem’s team generates x-rays with a “table-top” laser. They begin by focusing an intense laser beam on a cell containing gas under high pressure. The laser excites electrons in the gas and recaptures their energy, yielding very short pulses of high-frequency x-rays at multiples (harmonics) of the laser’s original energy.

While high-harmonic generation with Belkacem’s laboratory-scale laser can generate high-energy pulses, beam intensity is low and the pulse repetition rate is limited to 50 hertz (50 times a second). Nevertheless the x-ray beams open new pathways for spectroscopy.

“X-rays excite an atom’s core electrons; that’s both the strength and the technical challenge of multidimensional x-ray spectroscopy,” Belkacem says. He compares the challenge to a soccer match: “You want the x-rays to be spectators that will report how the game is being played – not become players themselves. Since the chemistry is in the valence electrons, somehow you have to use x-rays to involve the core electrons for atom specificity, but without letting them dictate the electron dynamics or the charge migration.”

A neon atom has two electrons in the 1s orbital, two in the 2s orbital, and six in the 2p orbital; the 3 shell is normally unoccupied. In the first test of nonlinear multidimensional spectroscopy with neon, Belkacem?s team will boost an electron in the relatively low-energy 2s orbital into the 3p orbital, an excited valence state. Within quadrillionths of a second a 2p electron will fill the 2s ?hole,? so that when the 3p electron relaxes, it will emit a photon signaling the transaction.

To tag a specific kind of atom’s valence electrons, Belkacem uses a powerful nonlinear spectroscopic technique called stimulated coherent Raman scattering, which has already been well established in the infrared and visible-light regions of the spectrum. The trick is to tune the first x-ray photon, the probe, so that it boosts a core electron to a higher orbital without kicking it right out of the atom and leaving an excess of positive charge. A lower-energy electron can then be stimulated down with a second x-ray to fill the hole, leaving the atom in a state of valence excitation.

Jumping the orbitals

To assess critical needs for future light sources, Belkacem and his team will first examine the electronic states of neon, which he calls “an ideal test bed” to prove the feasibility of the approach.

Electrons are arranged in specific orbitals, outward from an atom’s nucleus, and are designated by their spin, orientation, and energy. Neon has 10 electrons, two in the inner “1s” shell and (like almost all noble gases) eight in its valence shell, the outer “2” shell. The two electrons in the inner shell, plus two more in the valence shell, are in s orbitals (the 1s and 2s orbitals). The remaining six valence electrons are in 2p orbitals.

In the experiment, an x-ray photon tuned to the energy of the 2s shell will boost an electron into the neon atom’s previously unoccupied 3p shell. This needs energy on the order of 45 electron volts – a factor 20 to 30 times higher than typically used in the visible-light range. Within femtoseconds (quadrillionths of second), a second x-ray is sent to stimulate one of the 2p electrons into the hole. This fills the 2s shell but leaves behind an excited valence state – which, when the electron in the 3p orbital relaxes by emitting a characteristic photon, signals the experimenters.

As a noble gas, neon is nonreactive and forms molecules only with itself. “But once we’ve established the principle with neon, we plan to test the system on water and on carbon dioxide. In these studies the question will be, can we tag the oxygen atoms?” says Belkacem.

“In our final experiment, we’ll use three beams. The first pair will excite the atoms we want to follow in time, and the third will let us track how the valence states at different sites in the compound are coupled as the process evolves in space.”

Performing these kinds of experiments will require more powerful lasers than those in Belkacem’s present high-intensity, high-harmonic laser laboratory in Building 2. A much more powerful laser, capable of high-quality harmonics, is now under construction in the laboratory immediately adjacent.

The new laser’s main goal will be to address questions of crucial interest to designers of the next generation of FEL-based soft-x-ray light sources. Says Belkacem, “There are still many questions about what harmonics we should use for seeding FELs” – seeding is a technique for attaining specific higher energies – “what harmonic powers are needed, and how can we produce these high quality, high intensity harmonics at very high repetition.”

For a next-generation light source, says Belkacem, these questions are no more rhetorical than the question “What is chemistry?” itself. “To do the kind of chemistry we and many other researchers need to understand fundamental processes, we must identify the most critical of the various capabilities of a next-generation light source – those that will enable the most transformational science from the outset.”

Belkacem’s laser studies not only break ground for a new way of doing chemical research in the lab, they are critical to establishing what America’s premier facilities for doing this and many other kinds of science will be in future. One-of-a-kind new technology on the laboratory scale will open a new path to crucial experiments at chemistry’s leading edge.

Provided by Lawrence Berkeley National Laboratory (news : web)