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Posts Tagged ‘MOF’

Tuesday, November 4, 2014 @ 01:11 PM gHale

There is a new technique under development that could improve the efficiencies of photovoltaic materials and help make solar electricity cost-competitive with other sources of energy.

The work builds on Sandia National Laboratories’ success with metal-organic framework (MOF) materials by combining them with dye-sensitized solar cells (DSSC).

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“A lot of people are working with DSSCs, but we think our expertise with MOFs gives us a tool that others don’t have,” said Sandia’s Erik Spoerke, a materials scientist with a focus on solar cell exploration.

Sandia earned a $1.2 million award through U.S. Department of Energy’s SunShot Next Generation Photovoltaic Technologies III program, which sponsors projects that apply promising and proven basic materials science at the materials properties level to demonstrate photovoltaic conversion improvements to address or exceed SunShot goals.

The SunShot Initiative is a collaborative national effort that drives innovation with the aim of making solar energy fully cost-competitive with traditional energy sources before the end of the decade. Through SunShot, the Energy Department supports efforts by private companies, universities and national laboratories to drive down the cost of solar electricity to 6 cents per kilowatt-hour.

Dye-sensitized solar cells, invented in the 1980s, use dyes designed to efficiently absorb light in the solar spectrum. The dye ends up mated with a semiconductor, typically titanium dioxide, that facilitates conversion of the energy in the optically excited dye into usable electrical current.

DSSCs are a significant advancement in photovoltaic technology since they separate the various processes of generating current from a solar cell. Michael Grätzel, a professor at the École Polytechnique Fédérale de Lausanne in Switzerland, won the 2010 Millennium Technology Prize for inventing the first high-efficiency DSSC.

“If you don’t have everything in the DSSC dependent on everything else, it’s a lot easier to optimize your photovoltaic device in the most flexible and effective way,” said Sandia senior scientist Mark Allendorf. DSSCs can capture more of the sun’s energy than silicon-based solar cells by using varied or multiple dyes and also can use different molecular systems, Allendorf said.

“It becomes almost modular in terms of the cell’s components, all of which contribute to making electricity out of sunlight more efficiently,” Spoerke said.

Though a source of optimism for the solar research community, DSSCs possess certain challenges the Sandia research team thinks they can overcome by combining them with MOFs.

Allendorf said researchers hope to use the ordered structure and versatile chemistry of MOFs to help the dyes in DSSCs absorb more solar light, which he said is a fundamental limit on their efficiency.

“Our hypothesis is that we can put a thin layer of MOF on top of the titanium dioxide, thus enabling us to order the dye in exactly the way we want it,” Allendorf said. That should avoid the efficiency-decreasing problem of dye aggregation, since the dye would then lock into the MOF’s crystalline structure, he added.

MOFs are highly-ordered materials that also offer high levels of porosity, said Allendorf, a MOF expert and 29-year veteran of Sandia. He called the materials “Tinkertoys for chemists” because of the ease with which new structures can end up envisioned and assembled.

Allendorf said the unique porosity of MOFs will allow researchers to add a second dye, placed into the pores of the MOF, that will cover additional parts of the solar spectrum not covered with the initial dye. Finally, he and Spoerke feel MOFs can help improve the overall electron charge and flow of the solar cell, which currently faces instability issues.

“Essentially, we believe MOFs can help to more effectively organize the electronic and nano-structure of the molecules in the solar cell,” Spoerke said. “This can go a long way toward improving the efficiency and stability of these assembled devices.”

The technique is important in that it offers a pathway for highly controlled materials chemistry with potentially low-cost manufacturing of the DSSC/MOF process, Spoerke said.

“With the combination of MOFs,” Spoerke said, “dye-sensitized solar cells and atomic layer deposition, we think we can figure out how to control all of the key cell interfaces and material elements in a way that’s never been done before.”

Friday, May 24, 2013 @ 04:05 PM gHale

A newly synthesized material might provide an improved method for separating the highest-octane components of gasoline.

The material is a metal-organic framework (MOF) which is like a sponge with microscopic holes, said creator Jeffrey Long, professor of chemistry at the University of California, Berkeley.

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The innumerable interior walls of the MOF form triangular channels that selectively trap only the lower-octane components based on their shape, separating them easily from the higher-octane molecules in a way that could prove far less expensive than the industry’s current method. The Long laboratory and UC Berkeley applied for a patent on the MOF, known by its chemical formula, Fe2(bdp)3.
High-octane gasolines, the ultra or premium blends at fueling stations, are more expensive than regular unleaded gasoline due to the difficulty of separating out the right type of molecules from petroleum.

Petroleum includes several slightly different versions of the same molecule that have identical molecular formulae but varying shapes: Called isomers. Creating premium fuel requires a refinery to boil the mixture at precise temperatures to separate the isomers with the most chemical energy. The trouble is, four of these isomers — two of which are high octane, the other two far lower — have only slightly different boiling points, making the overall process challenging and costly.

The new MOF, however, could allow refineries to sidestep this problem by essentially trapping the lowest-octane isomers while letting the others pass through. The lowest-octane isomers are more linear and can nestle closer to the MOF walls, so when a mixture of isomers passes through the MOF, the less desired isomers stick to its surface — like the way a wet piece of paper sticks to a wall.

Matthew Hudson and his colleagues at the National Institute of Standards and Technology (NIST) Center for Neutron Research (NCNR) used neutron powder diffraction, a technique for determining molecular structure, to explore why the MOF has the right shape to selectively separate the isomers. Their research validated the team’s model of how the MOF adsorbs the low-octane isomers.

“It’s easier to separate the isomers with higher octane ratings this way rather than with the standard method, making it more efficient,” said Hudson, a postdoctoral fellow at the NCNR.

“And based on the lower temperatures needed, it’s also far less energy-intensive, meaning it should be less expensive.” Hudson said while industrial scientists will need to work out how to apply the discovery in refineries, the new MOF appears to be robust enough in harsh conditions to see use repeatedly a great many times, potentially reducing the necessary investment by a petroleum company.

Thursday, April 18, 2013 @ 06:04 PM gHale

Natural gas storage is one hurdle facing adoption of the energy source to becoming commercially viable.

One chemist, chemist Hongcai Joe Zhou, from Texas A&M wants to solve that issue which could bode well for sectors ranging from energy and economics to global relations and preservation.

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“We should invest in this for security reasons so we don’t have to rely on countries that may not be our allies for petroleum and for environmental reasons, since a large part of air pollution comes from the transportation sector,” Zhou said. “Government policy can help. However, the ultimate determining factor is that it has to be commercially viable. If it’s too expensive, few will use it.”

Natural gas tanks for passenger vehicles, for instance, currently are large and clunky, and no one wants to buy an ugly car, Zhou said. A key technical hurdle is making the natural gas, which is less dense than petroleum because it’s in the gaseous state, fit in roughly the same space that a conventional petroleum gas tank occupies, he said.

With the help of a $3 million Department of Energy grant, Zhou and his team are collaborating with automobile giant General Motors (GM), Lawrence Berkeley National Laboratory (LBNL) and Research Triangle Institute (RTI) to figure out how to take such a fuel tank from concept to reality.

Creating the necessary infrastructure to store and pump natural gas into vehicles would be costly, so Zhou said the solution is to use the existing natural gas infrastructure that runs through the homes and garages of millions of Americans for household uses, such as heating, cooling and cooking. The problem is natural gas from those lines comes out at such a low pressure that it needs to be compressed to get it to the pressure it needs to be stored at in the fuel tank, a costly process. The trick: Build a fuel tank that can store low-pressure natural gas, which is why Zhou is using his expertise in inorganic chemistry.

Zhou and his Texas A&M research group are working to adapt porous material to store a larger amount of the gas in the fuel tank and then let it out when needed. The key is to find the right kind of adsorbent, a type of substance that attaches atoms, ions or molecules to its surface. Zhou specializes in porous polymer networks (PPN) and metal-organic frameworks (MOF), which are crystalline frameworks consisting of metal ions along with ions or molecules that bind to the metal ions or organic ligands. Pores inside the MOF can work for gas storage.

“This is high-risk, high-reward research,” Zhou said. “It’s going to take some time to overcome some of the technical challenges.”

Friday, March 30, 2012 @ 12:03 PM gHale

A newly created material has the ability to separate closely related components of natural gas from one another, a task that currently demands a great deal of energy to accomplish. The material could end up improving the efficiency of the distillation process.

The material is a new type of metal-organic framework (MOF), a class of materials whose high surface area and tunable properties make them promising for applications as varied as gas storage, catalysis and drug delivery.

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This iron-based MOF, which the research team refers to as Fe-MOF-74, started in the lab of Jeffrey Long, a professor of chemistry at the University of California Berkeley, and analyzed by the team at the National Institute of Standards and Technology (NIST) and the Australian Nuclear Science and Technology Organization’s Bragg Institute.

Natural gas taken straight from the ground consists of a complex mixture of molecules called hydrocarbons, only some of which see use in any specific product such as fuel or plastic.

Separating the lighter types of hydrocarbon from one another — propane and ethylene, for example — is difficult because their weights are so similar. Currently, the most effective separation method involves chilling light hydrocarbons down to the point where they all liquefy, sometimes as low as 100 degrees below zero Celsius, and waiting until the heavier liquids settle below the lighter ones.

“A good percentage of the energy needed for separation goes to the cooling process,” said Wendy Queen, a postdoctoral fellow at the NIST Center for Neutron Research. “A material that can selectively adsorb light hydrocarbons could offer significant energy savings, making separation more economical.”

Through a microscope, Fe-MOF-74 looks like a collection of narrow tubes packed together like drinking straws in a box. Each tube consists of organic materials and six long strips of iron, which run lengthwise along the tube.

The team’s analysis shows different light hydrocarbons have varied levels of attraction to the tubes’ iron, a finding that researchers can exploit for separation. By passing a mixed-hydrocarbon gas through a series of filters made of the tubes, researchers can remove the hydrocarbon with the strongest affinity in the first filter layer, the next strongest in the second layer, and so on.

“It works well at 45 degrees Celsius, which is closer to the temperature of hydrocarbons at some points in the distillation process,” Queen said. “The upshot is that if we can bring the MOF to market as a filtration device, the energy-intensive cooling step potentially can be eliminated. We are now trying out metals other than iron in the MOF in case we can find one that works even better.”

Wednesday, September 8, 2010 @ 06:09 PM gHale

Sugar, salt, and a little alcohol led to the discovery of a new class of nanostructures that could aid in gas storage and food and medical technologies.
The porous crystals are the first known all-natural metal-organic frameworks (MOFs) that are simple to make, said researchers at Northwestern University. Most other MOFs consist of petroleum-based ingredients, but the Northwestern MOFs you can pop into your mouth and eat, and the researchers have.
“They taste kind of bitter, like a Saltine cracker, starchy and bland,” said Ronald A. Smaldone, a postdoctoral fellow at Northwestern and first co-author of a paper entitled, “Metal-Organic Frameworks from Edible Natural Products.” “But the beauty is that all the starting materials are nontoxic, biorenewable and widely available, offering a green approach to storing hydrogen to power vehicles.”
“With our accidental discovery, chemistry in the kitchen has taken on a whole new meaning,” said Sir Fraser Stoddart, Board of Trustees Professor of Chemistry in the Weinberg College of Arts and Sciences at Northwestern. The applications of this discovery cover cleaner air to healthier living, and it all comes from a product you can wash down the sink.
Metal-organic frameworks consist of well-ordered, lattice-like crystals. The nodes of the lattices are metals (such as copper, zinc, nickel or cobalt), and organic molecules connect the nodes. Within their very roomy pores, MOFs can effectively store gases such as hydrogen or carbon dioxide, making the nanostructures of special interest to engineers as well as scientists.
“Using natural products as building blocks provides a new direction for an old technology,” said Jeremiah J. Gassensmith, a postdoctoral fellow in Stoddart’s lab and an author of the paper.
“The metal-organic framework technology has been around since 1999 and relies on chemicals that come from crude oil,” said Ross S. Forgan, also a postdoctoral fellow in Stoddart’s lab and co-first author of the paper. “Our main constituent is a starch molecule that is a leftover from corn production.”
For their edible MOFs, the researchers use not ordinary table sugar but gamma-cyclodextrin, an eight-membered sugar ring produced from biorenewable cornstarch. The salts can be potassium chloride, a common salt substitute, or potassium benzoate, a commercial food preservative, and the alcohol is the grain spirit Everclear.
With these ingredients in hand, the researchers actually had set out to make new molecular architectures based on gamma-cyclodextrin. Their work produced crystals. Upon examining the crystals’ structures using X-rays, the researchers discovered they had created metal-organic frameworks.
“Symmetry is very important in metal-organic frameworks,” Stoddart said. “The problem is that natural building blocks are generally not symmetrical, which seems to prevent them from crystallizing as highly ordered, porous frameworks.”
It turns out gamma-cyclodextrin solves the problem: it comprises eight asymmetrical glucose residues arranged in a ring, which is itself symmetrical. The gamma-cyclodextrin and potassium salt dissolve in water and then crystallize by vapor diffusion with alcohol.
The resulting arrangement crystals consisting of cubes made from six gamma-cyclodextrin molecules linked in three-dimensions by potassium ions was previously unknown. The research team believes the strategy of marrying symmetry with asymmetry will carry over to other materials.
The cubes form a porous framework with easily accessible pores, perfect for capturing gases and small molecules. The pore volume encompasses 54 percent of the solid body.
“We achieved this level of porosity quickly and using simple ingredients,” Smaldone said. “Creating metal-organic frameworks using petroleum-based materials, on the other hand, can be expensive and very time consuming.”
“It is both uplifting and humbling to come to terms with the fact that a piece of serendipity could have far-reaching consequences for energy storage and environmental remediation on the one hand and food quality control and health care on the other,” Stoddart said.

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