Novel alloy could produce hydrogen fuel from sunlight

Scientists from the University of Kentucky and the University of Louisville have determined that an inexpensive semiconductor material can be "tweaked" to generate hydrogen from water using sunlight.

The research, funded by the U.S. Department of Energy, was led by Professors Madhu Menon and R. Michael Sheetz at the UK Center for Computational Sciences, and Professor Mahendra Sunkara and graduate student Chandrashekhar Pendyala at the UofL Conn Center for Renewable Energy Research. Their findings were published Aug. 1 in the Physical Review Journal (Phys Rev B 84, 075304).

The researchers say their findings are a triumph for computational sciences, one that could potentially have profound implications for the future of solar energy.

Using state-of-the-art theoretical computations, the UK-UofL team demonstrated that an alloy formed by a 2 percent substitution of antimony (Sb) in gallium nitride (GaN) has the right electrical properties to enable solar light energy to split water molecules into hydrogen and oxygen, a process known as photoelectrochemical (PEC) water splitting. When the alloy is immersed in water and exposed to sunlight, the chemical bond between the hydrogen and oxygen molecules in water is broken. The hydrogen can then be collected.

"Previous research on PEC has focused on complex materials," Menon said. "We decided to go against the conventional wisdom and start with some easy-to-produce materials, even if they lacked the right arrangement of electrons to meet PEC criteria. Our goal was to see if a minimal 'tweaking' of the electronic arrangement in these materials would accomplish the desired results."

Gallium nitride is a semiconductor that has been in widespread use to make bright-light LEDs since the 1990s. Antimony is a metalloid element that has been in increased demand in recent years for applications in microelectronics. The GaN-Sb alloy is the first simple, easy-to-produce material to be considered a candidate for PEC water splitting. The alloy functions as a catalyst in the PEC reaction, meaning that it is not consumed and may be reused indefinitely. UofL and UK researchers are currently working toward producing the alloy and testing its ability to convert solar energy to hydrogen.

Hydrogen has long been touted as a likely key component in the transition to cleaner energy sources. It can be used in fuel cells to generate electricity, burned to produce heat, and utilized in internal-combustion engines to power vehicles. When combusted, hydrogen combines with oxygen to form water vapor as its only waste product. Hydrogen also has wide-ranging applications in science and industry.

Because pure hydrogen gas is not found in free abundance on Earth, it must be manufactured by unlocking it from other compounds. Thus, hydrogen is not considered an energy source, but rather an "energy carrier." Currently, it takes a large amount of electricity to generate hydrogen by water splitting. As a consequence, most of the hydrogen manufactured today is derived from non-renewable sources such as coal and natural gas.

Sunkara says the GaN-Sb alloy has the potential to convert solar energy into an economical, carbon-free source for hydrogen.

"Hydrogen production now involves a large amount of CO2 emissions," Sunkara said. "Once this alloy material is widely available, it could conceivably be used to make zero-emissions fuel for powering homes and cars and to heat homes."

Menon says the research should attract the interest of other scientists across a variety of disciplines.

"Photocatalysis is currently one of the hottest topics in science," Menon said. "We expect the present work to have a wide appeal in the community spanning chemistry, physics and engineering."

Provided by University of Kentucky

Ultrasensitive particles offer new way to find cancer

About 10 years ago, scientists discovered a new type of genetic material called microRNA, which appears to turn genes on or off inside a cell. More recently, they found that these genetic snippets often go haywire in cancer cells, contributing to tumors’ uncontrollable growth.

A team of researchers at MIT has now engineered a way to detect abnormal microRNA levels in the blood of cancer patients, raising the possibility of developing a simple blood test to diagnose or monitor the disease.

The technology, described in two recent papers in the journals Analytical Chemistry and Angewandte Chemie, consists of an array of tiny particles, each designed to latch onto a specific type of microRNA. By exposing blood samples or purified RNA to these particles, the researchers can generate a microRNA profile that reveals whether cancer is present. Each type of cancer — lung, pancreas, and so forth — has its own microRNA signature.

MicroRNAs, which are usually only about 20 nucleotides long, have been implicated in many other diseases, including HIV, Alzheimer’s disease, diabetes and cardiovascular disease. The human genome contains about 1,000 microRNAs, believed to fine-tune gene expression by blocking the messenger-RNA molecules that carry DNA’s protein-building instructions.

While measuring microRNA levels has clear potential benefits, there are many challenges to detecting microRNA, says Patrick Doyle, a professor of chemical engineering at MIT and leader of the research team. “There’s not an accepted gold standard,” Doyle says. “Everybody has their own favorite one.”

Fishing for microRNA

Most current microRNA-detection techniques require RNA to be isolated from a blood or tissue sample and purified — a time-consuming process. Detecting microRNA directly from a blood sample would be much more efficient, Doyle says.

In their Angewandte Chemie paper, published in January, Doyle, graduate student Stephen Chapin and their colleagues showed that they could use tiny hydrogel particles, about 200 micrometers in length, to rapidly detect microRNA dysregulation patterns in RNA taken from four individuals with four different types of cancer. In their Analytical Chemistry paper, which went online this month, their particles successfully detected microRNA in the blood serum of a prostate cancer patient.

Hydrogels are made of networks of water-loving polymer chains, which are conducive to the attachment of nucleic acids. Each of the researchers’ particles is decorated with millions of identical strands of DNA that are complementary to a specific microRNA target sequence.

When the particles are mixed with a blood sample, any microRNA present binds to its complementary DNA. Each DNA strand also contains a short sequence that binds to a fluorescent probe, added later. Using a custom-built microfluidic scanner, the researchers then rapidly measure each particle’s fluorescence, revealing how much microRNA is present. The scanner also reads a chemical “barcode” imprinted on each particle, which reveals the type of microRNA being detected. The entire process takes less than three hours.

In their second paper, the researchers bumped up their particles’ sensitivity by amplifying the fluorescence generated by each particle. They achieved this by attaching multiple DNA label sequences to each microRNA target captured on the gel microparticles. These label sequences could then be attached to fluorescent probes.

This approach is 100 times more sensitive than other particle technologies for detecting microRNA, according to Doyle. The technology can detect as few as 10,000 copies of a particular microRNA, and each serum assay requires only 25 microliters of sample.

Jun Lu, an assistant professor of genetics at the Yale School of Medicine, says that level of sensitivity makes the particle system “a very promising technology.”

“The reported sensitivity can detect low levels of microRNAs present in serum, and likely other body fluids. This can make the technology very useful, considering that serum and several other body fluids require minimal invasive operations on patients,” says Lu, who was not involved in this research.

The new MIT approach also gives more accurate results than existing techniques that directly label microRNA strands with a fluorescent probe. Different microRNA sequences can take on different shapes, which affects how easily they bind to the fluorescent probe.

Doyle is now starting to work with medical researchers to investigate using microRNA detection to study other diseases such as cardiovascular disease and HIV. He and one of his former graduate students, Daniel Pregibon, have started a company, Firefly Bioworks, which has licensed the technology to build and scan the particles, with plans to develop the system for commercial use.
This story is republished courtesy of MIT News (http://web.mit.edu/newsoffice/), a popular site that covers news about MIT research, innovation and teaching.

Provided by Massachusetts Institute of Technology (news : web)

Breakthrough in hydrogen fuel cells: Chemists develop way to safely store, extract hydrogen

 A team of USC scientists has developed a robust, efficient method of using hydrogen as a fuel source.

Hydrogen makes a great fuel because of it can easily be converted to electricity in a fuel cell and because it is carbon free. The downside of hydrogen is that, because it is a gas, it can only be stored in high pressure or cryogenic tanks.

In a vehicle with a tank full of hydrogen, "if you got into a wreck, you'd have a problem," said Travis Williams, assistant professor of chemistry at the USC Dornsife College.

A possible solution is to store hydrogen in a safe chemical form. Earlier this year, Williams and his team figured out a way to release hydrogen from an innocuous chemical material — a nitrogen-boron complex, ammonia borane — that can be stored as a stable solid.

Now the team has developed a catalyst system that releases enough hydrogen from its storage in ammonia borane to make it usable as a fuel source. Moreover, the system is air-stable and re-usable, unlike other systems for hydrogen storage on boron and metal hydrides.

The research was published this month in the Journal of the American Chemical Society.

"Ours is the first game in town for reusable, air stabile ammonia borane dehydrogenation," Williams said, adding that the USC Stevens Institute is in the process of patenting the system.

The system is sufficiently lightweight and efficient to have potential fuel applications ranging from motor-driven cycles to small aircraft, he said.

More information: A Robust, Air-Stable, Reusable Ruthenium Catalyst for Dehydrogenation of Ammonia Borane, J. Am. Chem. Soc., Article ASAP.
DOI: 10.1021/ja2058154

Abstract
We describe an efficient homogeneous ruthenium catalyst for the dehydrogenation of ammonia borane (AB). This catalyst liberates more than 2 equiv of H2 and up to 4.6 system wt % H2 from concentrated AB suspensions under air. Importantly, this catalyst is robust, delivering several cycles of dehydrogenation at high [AB] without loss of catalytic activity, even with exposure to air and water.

Provided by University of Southern California (news : web)

Researchers expand capabilities of miniature analyzer for complex samples

It’s not often that someone can claim that going from a positive to a negative is a step forward, but that’s the case for a team of scientists from the National Institute of Standards and Technology (NIST) and private industry. In a recent paper,* the group significantly extended the reach of their novel microfluidic system for analyzing the chemical components of complex samples. The new work shows how the system, meant to analyze real-world, crude mixtures such as dirt or whole blood, can work for negatively charged components as well as it has in the past for positively charged ones.

In previous work,** NIST researchers Elizabeth Strychalski and David Ross, in collaboration with Alyssa Henry of Applied Research Associates Inc. (Alexandria, Va.), demonstrated the use of a technique called GEMBE (for “gradient elution moving boundary electrophoresis”) for analyzing complex samples. The NIST-developed system combines a simple microfluidic structure (two reservoirs connected by a microchannel), electrophoresis (which uses electricity to move sample components through a fluid) and pressure-driven flow.

Analyzing complex samples can be difficult because components in these samples (such as the fat globules in milk or proteins in blood) can “foul” or contaminate microfluidic channels. The traditional solution has been to remove contaminants with costly, time-consuming sample preparation prior to analysis.

GEMBE solves this problem by pumping fluid through the microchannel using a controlled pressure in the direction opposite to electrophoresis. This opposing pressure-driven flow acts as a "fluid gate" between the sample reservoir and the microchannel. Gradually reducing the pressure of the counterflow opens the "gate" a little bit at a time. A specific sample component is detected when the pressure flow becomes weak enough—i.e. the "gate" opens wide enough—that the component’s electrophoretic motion pushes it against the pressure-driven flow and into the channel for detection. In this way, different components enter the channel at different times, based on their particular electrophoretic motion. Most importantly, the channel doesn’t become fouled because the unwanted components in the sample are held out.

“Previously, we validated the GEMBE technique by quantitatively analyzing components from complex samples in solution that were cationic [positively charged] and could, therefore, be separated relatively easily from anionic [negatively charged] contaminants in a mixture,” Strychalski says. “However, we needed a way to make GEMBE work when both the desired components and the contaminants are negatively charged.”

For some samples, Strychalski says, this was achieved by choosing a different solution pH to change the electrophoretic motion of the unwanted components. In other cases, the addition of commercially available surface coatings to the sample did the trick without compromising the ease and robustness of the GEMBE technique.

“Additives can be selected that will interact with material in the sample that we don’t want to study,” Strychalski explains. “If we choose the right coating, it will slow the electrophoretic motion of contaminants relative to the desired components. This prevents the former from interfering with analysis while still allowing the latter to enter the microchannel for detection.”

Strychalski and her colleagues plan to continue refining the GEMBE system, including an effort to define which surface coatings optimize the technique for specific components in a variety of complex samples.

More information: E.A. Strychalski, et al. Expanding the capabilities of microfluidic gradient elution moving boundary electrophoresis for complex systems. Analytical Chemistry, Vol. 83, No. 16, pp 6316–6322. Aug. 15, 2011.

See “‘No Muss, No Fuss’ Miniaturized Analysis for Complex Samples Developed” http://www.physorg … 7763391.html

Provided by National Institute of Standards and Technology (news : web)

Panda poop may be a treasure trove of microbes for making biofuels

 

Panda poop contains bacteria with potent effects in breaking down plant material in the way needed to tap biomass as a major new source of “biofuels” produced not from corn and other food sources, but from grass, wood chips and crop wastes, scientists reported today at the 242nd National Meeting & Exposition of the American Chemical Society (ACS).

“Who would have guessed that ‘panda poop’ might help solve one of the major hurdles to producing biofuels, which is optimizing the breakdown of the raw plant materials used to make the fuels?” said study co-author Ashli Brown, Ph.D. “We hope our research will help expand the use of biofuels in the future and help cut dependency on foreign oil. We also hope it will reinforce the importance of wildlife conservation.”

Brown pointed out that bacteria from the giant panda are particularly promising for breaking down the super-tough plant material known as lignocellulose in switch grass, corn stalks and wood chips. That advance could speed the development of so-called cellulosic biofuels made from these tough plant materials in a way that doesn’t rely on precious food crops such as corn, soybeans and sugar now used for making biofuels, she noted.

Scientists have long known that giant pandas — like termites and cattle — have bacteria in their digestive systems to break down the cellulose in plants into nutrients. Bamboo constitutes about 99 percent of the giant panda’s diet in the wild. An adult may eat 20-40 pounds of bamboo daily — leaves stems, shoots and all. Until the energy crunch fostered interest in biofuels, however, scientists never thought to parse out exactly what microbes in the giant panda gastrointestinal system were involved in digestion.

Brown and colleagues, including graduate student Candace Williams, collected and analyzed the fresh feces of a pair of male and female pandas at the Memphis Zoo for over a year. They identified several types of digestive bacteria in the panda feces, including some that are similar to those found in termites, which are renowned for their ability to digest wood.

“Our studies suggest that bacteria species in the panda intestine may be more efficient at breaking down plant materials than termite bacteria and may do so in a way that is better for biofuel manufacturing purposes,” said Brown, who is with Mississippi State University.

Based on other studies, Brown estimated that under certain conditions these panda gut bacteria can convert about 95 percent of plant biomass into simple sugars. The bacteria contain enzymes — highly active substances that speed up chemical reactions — so powerful that they can eliminate the need for high heat, harsh acids and high pressures currently used in biofuel production processes, she said. Those processes also tend to be time- and energy-intensive, as well as expensive. Panda bacteria could therefore provide a faster, cleaner and less costly way to make biofuels.

Brown is currently trying to identify every intestinal bacterium in the giant panda in order to isolate the most powerful digestive enzymes for biofuel production and other purposes. She noted that scientists could use well-established genetic engineering technology to put the genes that produce those enzymes into yeasts. The yeasts then would produce the enzymes and could be grown on a commercial scale to provide large amounts of enzymes for a biofuel industry.

“The discovery also teaches a lesson about the importance of biodiversity and preserving endangered animals,” Brown said, noting that less than 2,500 giant pandas remain in the wild and about 200 are in captivity. “Animals and plants are a major source of medicines and other products that people depend on. When we lose them to extinction, we may lose potential sources of these products.”

The U.S. Department of Energy, The Memphis Zoological Society, the Mississippi Corn Promotion Board, and the Southeastern Research Center at Mississippi State provided funding for this study.

Provided by American Chemical Society (news : web)