By Patti Koning
It’s every chemist’s dream — arranging and rearranging molecular pieces into controlled structures. Mark Allendorf (8324) and other chemists at Sandia have made that dream a reality through a highly successful Laboratory Directed Research and Development project that has yielded exciting results and a few surprises.
Those molecular tinker toys are metal-organic frameworks or MOFs, a new class of nanoporous materials. “For many years people have tried to make porous materials out of a combination of organic and inorganic pieces but were never able to achieve permanent porosity,” says Mark.
Then came MOFs. These materials, formed from seemingly modest chemical components, have generated big results for Mark and his team. An LDRD project to study MOFs as a discovery platform for confined space chemistry has, in less than three years, resulted in outside funding, two patent applications, six publications with more in submission, and three major findings.
MOFs were discovered in 1999 by Omar Yaghi, who was a professor at the University of Michigan at the time (he has been at UCLA since 2006). MOFs are positively charged metal cations that are linked to anionic organic groups, which are called a coordination bond. Yaghi learned that by properly selecting the structure of the organic component and the coordination geometry of the metal, he could condense them into crystals with specific morphologies that preserve their porosity.
“The first MOF that Yaghi reported was pretty spectacular. It has a surface area more than three times that of industrial-grade molecular sieves, such as zeolites,” says Mark. “It really does look like tinker toys.”
In late 2005, with a little less than $500,000 in annual LDRD funding for three years, Mark, Blake Simmons (8755), Jeffery Greathouse (6316), and several postdocs began brainstorming research avenues to pursue. The problem was not coming up with ideas, but finding the resources to pursue all of their ideas.
“We felt like kids in a candy store, with all of this low-hanging fruit,” Mark adds.
A new class of scintillators
One of the first areas they pursued was a fluorescent framework, which could be used as a sensing mechanism. Postdoc Christina Bauer created two new MOFs, both of which were fluorescent and one of which was porous, a result that Mark says was satisfying in its own right.
Then, at a talk she gave on the new MOFs, Patrick Doty (8772) observed that they contain stilbene, a well-known scintillator. This got him wondering if the new MOFs could be used as a scintillator.
Patrick tested the MOFs and the results were better than anyone had anticipated. They not only scintillated, but they performed so well that they turned out to be the first truly new class of scintillators found in decades.
“What is really exciting is that these structures have scintillation built into the framework, but because they are porous you can add other materials,” says Mark. “For example, you could shift the wavelength of the scintillation light to a more convenient area, making it easier to detect, or add helium-3 (He-3) gas to make radiation detection more efficient.”
Once again, the researchers had that kid-in-a-candy-store feeling, as the new scintillators opened up a whole raft of ideas that would be difficult to pursue with other materials. Earlier this year, the Defense Threat Reduction Agency (DTRA) agreed to fund a Sandia proposal to build a better understanding of the fundamental processes controlling neutron-generated scintillation in MOFs. This is a particularly important research area because neutrons are emitted by fissionable material but are difficult to detect using current materials that can only detect the highest energy or slowest neutrons.
“In less than three years, the original LDRD had already pulled in outside funding, which is pretty unusual,” Mark says.
Microcantilevers springboard chemical detection
Another big result was in chemical detection. Some MOFs can shrink by up to 10 percent when water is added without actually changing their crystal structure.
“For a sensor, if you take a material that changes its dimension when it absorbs something and mate it with another material, the absorption will create a stress at the interface between the two materials,” explains Mark. “You can then detect that stress using a piezo resistance sensor.”
He formed a collaboration with Peter Hesketh, a mechanical engineering professor at Georgia Tech who works on microcantilevers (approximately 40 microns wide by 100-300 microns long) machined using MEMS technology. As Mark explains, the challenge of microcantilevers is making them responsive to specific stimuli. One method is to put organic polymers on top of the microcantilever, but those materials are not porous.
“MOFs are porous and rigid in comparison with an organic polymer. We hypothesized that if we could glue an MOF layer onto the microcantilever surface so that there was no slip, then we would be able to very sensitively detect absorbed molecules,” he says.
After nearly two years of work, the researchers were able to apply a uniform layer of MOFs onto the microcantilever. It then took several months to prove that they had indeed accomplished their task. The small size of microcantilevers means that most analytical techniques don’t work.
The results, again, were stunning. The MOF-coated microcantilever responds in less than a second to water vapor, ethanol, and methanol and does so differentially, meaning that the response is unique to the chemical detected. The researchers also found that if they baked out the water, they opened up binding sites in the MOF and turned on sensitivity to carbon dioxide.
“We see resistance changes in these sensors that are very fast and extremely reversible — almost square-wave type behavior,” says Mark. “As far as I know, this is the first time anyone has ever integrated an MOF with a real device. We not only built a sensor, but we also proved it responds reversibly and that it has actual selectivity by controlling the hydration state of the layer.”
The team submitted a patent application and a journal article describing the results is currently being reviewed.
A potential application is for breath analysis. A symptom of pulmonary distress, especially in children, is increased levels of nitric oxide and carbon monoxide in the breath. Mark envisions a device based on an MOF microcantilever that could detect dangerous levels in a doctor’s office or even at home. The team has submitted proposals to pursue this application to the National Institutes of Health.
Jeffery led the third major accomplishment from the original MOF LDRD — development of a computational tool that enables prediction of how MOFs would react when they adsorb gases. As Mark explains, this had been done before but always under the approximation that the framework atoms were fixed at their crystallographic coordinates.
Jeffery wanted to look at reactivity so he invented a flexible force field to allow MOF atoms to move during the simulation and to reproduce the structural changes that result from adsorption of various molecules.
“Our force-field approach has led to new insight into the physical and mechanical properties of MOFs, such as the unusual trend of negative thermal expansion,” he says.
The project team has published several papers, including two in the Journal of the American Chemical Society. The first paper, on water reactivity with MOFs, had 17 citations within the first 18 months of publication.
A bright future
The potential applications for MOFs seem to be limited only by the imagination of the researchers. Research is underway on chemical separations, other gas storage that could include CO2 sequestration, and catalysts. More distant applications include drug delivery devices, since some MOFs react with water and fall apart in aqueous solutions, and personal exposure monitors.
“This is the first time in my 22-year career that I’ve been involved in really hot science,” says Mark. “It’s pretty fun.” -- Patti Koning
By Mike Janes
Sandia has proven to be a leading research authority when it comes to the protection of transportation hubs and large facilities against chemical or biological attack. Projects involving San Francisco International Airport and McAfee Stadium come to mind, among others.
But a terrorist event of this nature, particularly of the biological sort, could be even more catastrophic if it were carried out over a wide area, such as a large city or metropolitan region. That’s one of the main reasons why Sandia’s systems analysts and decontamination and restoration experts have been engaged in a four-year, Department of Homeland Security (DHS) and DoD-funded effort to help authorities deal with the aftermath of a biological attack.
The Interagency Biological Restoration Demonstration (IBRD) is a collaborative program to develop policies, plans, and technologies required to restore large urban areas in the event of a wide-area biological release, with a focus on civilian-military interfaces. This program is initially using the Seattle/Tacoma urban area and local military bases, such as Fort Lewis and McChord Air Force Base, in a case study. Study findings and results could potentially be applied nationally to biological restoration policy and programs.
Sandians at both the New Mexico and California sites are involved in the IBRD effort, along with key partners from Lawrence Livermore and Pacific Northwest national laboratories and oversight from DHS’ Directorate for Science and Technology (S&T) and DoD’s Defense Threat Reduction Agency (DTRA) program offices.
Gaps need to be addressed
“An anthrax attack would obviously present a huge problem for any city,” says systems analyst Lynn Yang (8114), who notes that Seattle and the surrounding Puget Sound region has been the focus of the IBRD team’s initial efforts.
“You’re talking about potentially hundreds of buildings and tens of square miles. Some regions may face a general lack of resources available to fulfill all the restoration demands in a timely fashion,” Lynn says.
Sandia and the rest of the IBRD team have been tackling the problem for about a year now. One of the initial “knowledge gaps” identified by the analysis team was that authorities currently do not know whether a contaminated outdoor area would need to be actively decontaminated, or if natural attenuation from rain and ultraviolet exposure would be sufficient. The team also has made recommendations in planning and decision making. For example, in a wide-area contamination scenario, authorities would greatly benefit from formal, agreed-upon processes to determine what buildings need attention, and in what order.
Without such processes, a city hit by an anthrax attack might attempt to clean up buildings and infrastructure in an inefficient manner. Sandia analysts have recommended that decision prioritization for cleanup should be informed by many factors, including the overall objective for restoration (e.g., maximum reoccupation in minimum amount of time), an understanding of what infrastructure is critical, and other local considerations.
To address the wide-area dilemma, Sandia has further recommended to its sponsors that they improve the technologies available to “scope” the problem more rapidly following an event.
Wayne Einfeld (6327), along with others in Sandia’s systems analysis group in California, is leading a study that is making specific recommendations to the program sponsors as to which technologies should be considered for development and what capabilities would be most beneficial. “As is usually the case, federal resources are limited, so program managers must carefully choose where to invest in technology development and application to make the biggest impact in the restoration process,” says Wayne. The analysis team is using a variety of analytical tools to provide quantitative justification for the various development options.
The IBRD team at Sandia, led by principal investigator Mark Tucker (6327), is also involved in technology development. Mark has a long history in restoration technology, having led the development of the Labs’ well-known decontamination formulation that has since been commercialized and widely used in both military and domestic applications.
Managing contaminated waste
One piece of technology that’s already been used to a large degree, Mark says, is the Sandia-developed Analyzer for Wide-Area Restoration Effectiveness, or AWARE. Currently in spreadsheet format, AWARE is a tool that looks across the full spectrum of restoration activities and analyzes each phase in terms of resources and timelines. It explores the answers to questions such as, how many teams are required to take samples in a given location. If a certain technology is introduced, does it improve or speed up the process?
Another area of focus for IBRD, Lynn says, has been how best to manage the equipment and other items in contaminated zones. Given the quantity and variation of items, including cars, furniture, and other pieces of personal property and goods that may be present, policies need to be developed that help decide what items should be disposed of (versus decontaminated). Other issues faced by decision makers include which technologies will be used to decontaminate the various categories of items and the approved protocols for transporting and handling contaminated solid waste.
Mark, Lynn, Wayne, and the other IBRD team members, including Julie Fruetel (8125), David Franco (8125), Donna Edwards (8114), Bob Knowlton (6327), Rita Betty (6327), and John Brockmann (1532), now into their second year of the program, continue to write plans, develop technology recommendations, and develop new technologies and methods for the program sponsors. Independent working groups will be considering inputs from Sandia’s investigations as well as other interagency concerns to help DoD and DHS select technologies to pursue further under the IBRD program. — Mike Janes
By Mike Janes
Algae is one of several potential fuel sources being looked at to help solve the global energy crisis. It is attractive on several fronts: It’s easy to produce, it can be grown in regions that aren’t used for food, and it doesn’t need to compete with the same water used in crop irrigation. Most important, algae is rich in oils that can be used in biodiesel production.
“Biofuels derived from algae present an opportunity to dramatically impact US energy needs for transportation,” says Grant Heffelfinger (8330), who leads Sandia’s biofuels program.
It turns out, though, that for every advantage, there are disadvantages. For starters, understanding and characterizing the finicky mixture of oils, proteins, and hydrocarbons found in various species of microalgae is an enormous challenge. Second, the extraction of oils from the algae and their subsequent conversion into biodiesel fuels in an economically feasible way represent additional barriers.
Those challenges, however, are in the crosshairs of Sandia researchers involved in a Laboratory Directed Research and Development (LDRD) effort titled “Microalgal Biodiesel, Feedstock Improvement by Metabolic Engineering.” Led by molecular biologist Todd Lane (8321) and using advanced molecular biology techniques largely unavailable in years past, the effort’s aim is to create more effective harvesting, extraction, and conversion techniques for algae and the fuel-friendly oils they produce.
Algae, Todd says, yields the same kind of oils produced by certain vegetables and plants used for biodiesel conversion (as well as animal fats). The chemical composition of these oils includes triacylglyceride, or TAG, which is the key to the conversion to biofuel.
But algae only produces TAGs under very specific environmental conditions, or triggers, a scientific challenge that Todd and his colleagues are addressing.
“Algae only produce TAGs when they need to, basically as a storage defense mechanism, much like humans store fat,” says Todd. “We’re trying to trick the algae into thinking it’s continually experiencing starvation conditions so it will produce oils without interruption.” Once that hurdle is overcome, he says, “you’ve then opened the door to many possible growth and recovery techniques.”
Sandia has been looking at two microalgal organisms, Phaeodactylum tricornutum and Thalassiosira pseudonana, the genomes of which were recently sequenced by DOE’s Joint Genome Institute in northern California. The LDRD project’s intent, says Todd, is to take advantage of the new genetic information to better understand the processes involved in the formation of oils, then eventually to manipulate those processes to produce larger quantities of those oils.
Characterizing the oils, says Todd, involves both proteomic analysis (where the organisms are taken apart and the proteins separated onto gels) and transcriptional analysis (looking at the genes that are expressed even before the organism transitions into starvation conditions). Todd calls this important work the “molecular fingerprinting” of the oils contained in the algae, with the hope that researchers can soon use the information to engineer larger quantities of oil.
The LDRD team has recently completed a significant milestone where it compared the different metabolic routes of oil production in multiple strains of algae by tracking their accumulation as a function of time and environment. The results have produced new insight into the mechanisms of nutrient starvation in algae, and will serve as the basis for engineering the algae into robust oil producers. These findings were presented at an international conference on phycology (the scientific study of algae), and the team has just submitted a paper to the Journal of Applied Phycology that summarizes their conclusions.
Extraction: squeezing the oil out
There are several tried and true methods for extracting oils from algae, including mechanical, chemical, thermochemical, plasma, and microwave techniques. Most traditional methods are not considered to be long-term solutions. The mechanical approach, for example — which involves pressing algae to squeeze out the oil, much like the process for producing olive oils from olives — is highly power intensive and not scalable.
Sandia, Todd says, is mostly focused on the chemical approach, whereby solvents with a biological affinity toward oils are used, acting somewhat like a chemical sponge to “pull” the oils from the algae. This approach, which Sandia believes may be scalable, is fraught with its own obstacles, most notably the fact that the most effective solvents aren’t particularly good for the environment.
But a closed and highly controlled facility, similar to an oil refinery, might be able to handle the operation at an industrial level. “Refineries already produce these kinds of chemicals,” says Todd, “and we’d also be taking advantage of existing chemical engineering and systems engineering infrastructure.” Using the same technology by which hydrocarbons are distilled and separated to separate oils from algae and create “bio crude,” he says, would be a logical and easier way to move toward algae-based transportation fuels.
Another focus of the microalgal LDRD project is the “dewatering,” or drying, of the algae, an important consideration since this step — necessary for the conversion into fuel — is highly energy intensive and thus estimated to represent nearly 50 percent of the current processing cost. Sandia is also examining ways by which algae can be grown and harvested in the first place.
“Algae is easy enough to grow, but it’s expensive to do in a way that’s robust and scalable,” says Todd.
Two years into the three-year microalgal LDRD project, Todd says he and his colleagues have already come to a vastly better understanding of the starvation process that is so critical for the efficient production of oils derived from algae. These results will help build the genomic and biotechnology toolboxes that will be required for the optimization of algal oil production at the massive commercial scales required to meet the transportation fuel demands of the US.
“The simple goal with this project is to improve the yield of oil in these organisms (P. tricornutum and T. pseudonana), then go back and analyze what we’ve done and see if we can apply it to other organisms,” says Todd. Such an achievement, he says, could then be applied to other, more commercially viable organisms, adding considerably to the scientific knowledge base necessary for long-term algae-to-biofuels production. — Mike Janes
By Patti Koning
A new tool under development by Sandia researchers promises to transform the way nuclear reactors are monitored. The antineutrino detector, a joint project by Sandia and Lawrence Livermore National Laboratory (LLNL), has already proven it can perform continuous and independent monitoring of the operational status and thermal power of reactors.
Antineutrinos are the antiparticles of neutrinos — fast-moving elementary particles produced in nuclear decay with minuscule mass that pass through ordinary matter undisturbed. They are difficult to detect, but the sheer number a nuclear reactor emits is so large that a cubic-meter scale detector can record hundreds or even thousands per day.
In simple terms, the antineutrino detector tracks the rate of antineutrinos emanating from a reactor and provides direct measurement of the operational status (on/off) of the reactor, measures the reactor’s thermal power, and places a direct constraint on the fissile inventory of the reactor throughout its life cycle.
“You can’t fake the signal,” says Lorraine Sadler (8132), one of the Sandia researchers leading the effort. “The only source that produces a strong antineutrino signal is a nuclear reactor.”
David Reyna (8132), Sandia’s principal investigator on the project, describes neutrinos as annoying because they rarely interact with ordinary matter and can’t be shielded. “But this fact means you can sit outside the reactor itself, where the neutrinos are still flowing unobstructed, so it is a pure monitor of what exactly is happening inside without doing secondary measurements of temperature and back calculating,” he adds.
Joining David and Lorraine on the project are Adam Bernstein, the LLNL principal investigator, and his colleagues Nathaniel Bowden, Steven Dazeley and Robert Svoboda, along with professor Todd Palmer and graduate student Alex Misner at Oregon State University. Other Sandia contributors are Jim Brennan (8321), who performed the mechanical design of the detectors and assisted with assembly; John Steele (8227), who played a major role in the design of the electronics readout for the detector system, particularly the field-programmable gate-array (FPGA)-based trigger; Stan Mrowka (8132), who helped implement much of the software for the electronic readout; Kevin Krenz (8132), who designed and fabricated the gadolinium neutron absorbers in the recent plastic detector; and Jason Zaha (8132), who assisted with the design and fabrication of the electronic readout.
The antineutrino detector addresses a critical issue as more countries begin seeking nuclear power — that nuclear reactors and nuclear weapons use very similar fuels. The best-known and most challenging role of the International Atomic Energy Agency (IAEA) is verifying that nuclear states comply with their commitments under the Nuclear Non-Proliferation Treaty and other nonproliferation agreements, to use nuclear material and facilities only for peaceful purposes.
While IAEA nuclear weapons inspectors are “physicists, chemists, and engineers with decades of experience in nuclear weapons research and development, nuclear material safeguards, and intrusive international inspection,” according to IAEA Director General Mohamed El Baradei, they still face a daunting task. Today, monitoring occurs infrequently, usually every 18 months, and depends on administrative information provided by operators within nuclear facilities.
“The antineutrino detector provides a completely independent way of verifying what is happening inside a nuclear reactor,” says Lorraine. “This type of monitoring could make nuclear power a viable option to emerging societies.”
This spring researchers from Sandia and LLNL wrapped up a field test of the detector at the San Onofre Nuclear Generating Station, located midway between Los Angeles and San Diego. The antineutrino detector was placed in the tendon gallery of the reactor, outside the containment dome and about 25 meters from the core.
“The test was completely unobtrusive to the power plant, which is very important from the operators’ perspective,” says Lorraine. “Besides our direct contacts at the plant, other employees were even shocked when we told them we were still there.”
Once the detector is in place, the agency doing the monitoring, most likely the IAEA, can acquire data without any intervention or support from the reactor operator. While this test was a complete success, less than half of the reactors worldwide have a tendon gallery design. Work is already underway on detectors that can operate above ground.
“Above ground is a whole different monster,” says Lorraine. “Underground you are shielded from cosmic background, but above ground without the earth’s shielding, your background noise increases by orders of magnitude.”
The researchers currently are working on two separate projects. The first replaces half of the original underground detector, made from a liquid scintillator, with a plastic scintillator. A liquid scintillator poses some safety hazards, so if the same results can be achieved using a plastic scintillator, the technology would be ultimately easier to deploy.
A second set of experiments focuses on above-ground deployment by exploring two avenues: segmenting the existing detector materials to better distinguish external background from signal events, and a new high-sensitivity germanium-based detector technology that would be 1,000 times more sensitive to neutrino interactions by looking for a different signature.
“I’m confident we can get the same results above ground, but the technology hasn’t been tested yet,” says David.
The target application for the antineutrino detector is cooperative monitoring, but there is also a potential for far field monitoring. The current focus, says David, is on making the detector smaller and less invasive while maintaining consistent performance.
The antineutrino detector will likely be tested in more reactors soon. David says he is talking to the Columbia Generating Station in Washington and the Advanced Test Reactor at Idaho National Laboratory. Internationally, testing could occur in Canada and Brazil.
David and Lorraine, in collaboration with physics professor Juan Collar at the University of Chicago, are also investigating a new physical process called coherent neutrino-nucleus scattering for detecting antineutrinos that could potentially lead to large sensitivity gains in their antineutrino detector. This summer they have begun an experiment at San Onofre to verify this new antineutrino detection technique.They say they’re pleased with the results so far and excited about the potential of the antineutrino detector. Plus, adds Lorraine, its nice to know that neutrinos have a purpose. — Patti Koning