J. Mathias Weber

JILA’s Mathias Weber Named Fellow of the American Physical Society

Steven Burrows — Fri, 10 Oct 2025 15:42:26 +0000

JILA’s Mathias Weber Named Fellow of the American Physical Society Steven Burrows Fri, 10/10/2025 - 09:42

Steven Burrows / JILA Science Communications Manager

Mathias Weber.

JILA and the University of Colorado Boulder are proud to announce that Professor J. Mathias Weber has been elected a Fellow of the American Physical Society (APS), one of the highest honors in the physics community. This prestigious recognition is awarded to no more than 0.5% of APS members annually and celebrates exceptional contributions to the field of physics.

The APS citation highlights Weber’s “fundamental contributions to our understanding of molecular interactions and solvation effects in complex systems, obtained via elegant vibrational/electronic laser photodissociation spectroscopy of molecular and cluster ions in the gas phase.”

As a Fellow of JILA and a professor in ��Ҵ�ý�ƽ�� Department of Chemistry, Weber has long been at the forefront of chemical physics research. His work explores how molecules interact and behave in isolated environments, using advanced spectroscopic techniques to probe the structure and dynamics of ions and clusters. These insights have broad implications, from understanding atmospheric chemistry to designing novel materials.

Weber’s lab specializes in cryogenic ion spectroscopy, a technique that allows scientists to study molecular systems at extremely low temperatures, revealing subtle interactions that are often masked at room temperature. His recent work has shed light on how water molecules interact with aromatic systems, and how ion-receptor complexes behave in biologically relevant environments.

Originally from Germany, Weber earned his doctorate from the University of Kaiserslautern and completed postdoctoral research at Yale University before joining ��Ҵ�ý�ƽ��.

The APS Fellowship adds to a growing list of accolades for Weber, including the NSF CAREER Award and the Emmy-Noether Award from the German Research Foundation.

JILA congratulates Professor Weber on this well-deserved honor and celebrates the continued impact of his research on science and society.

JILA and the University of Colorado Boulder are proud to announce that Professor J. Mathias Weber has been elected a Fellow of the American Physical Society (APS), for fundamental contributions to our understanding of molecular interactions and solvation effects in complex systems, obtained via elegant vibrational/electronic laser photodissociation spectroscopy of molecular and cluster ions in the gas phase.

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Molecular Lock and Key: Decoding the Secrets of Ion Binding

Steven Burrows — Wed, 09 Apr 2025 18:25:48 +0000

Molecular Lock and Key: Decoding the Secrets of Ion Binding Steven Burrows Wed, 04/09/2025 - 12:25

Kenna Hughes-Castleberry / JILA Science Communicator

Understanding how molecules interact with ions is a cornerstone of chemistry, with applications from pollution detection and cleanup to drug delivery. In a series of new studies led by JILA Fellow and University of Colorado Boulder chemistry professor Mathias Weber, researchers explored how a specific ion receptor called octamethyl calix[4]pyrrole (omC4P) binds to different anions, such as fluoride or nitrate. These findings, published in The Journal of the American Chemical Society, The Journal of Physical Chemistry Letters, and The Journal of Physical Chemistry B, provide fundamental insights about molecular binding that could help advance fields such as environmental science and synthetic chemistry.

“The main issue with understanding these interactions is that there is a competition between an ion binding to a certain receptor and that same ion wanting to be surrounded by solvent molecules,” Weber explains. “This competition impacts how effective and specific an ion receptor can be, and we currently don’t understand it sufficiently well to design better ion receptors for applications. This has been a problem for decades, and we can now try to solve it by taking a different perspective.”

Looking at Ion Receptors

The test molecule in question, omC4P, is a prototypical anion receptor that has received much interest for nearly 30 years, a macrocyclic molecule with a cup-like structure designed to capture negatively charged ions (anions). Its rigid yet adaptable cavity contains four NH groups that form hydrogen bonds with incoming ions, making it an ideal system for investigating how different anions interact with molecular hosts.

What makes omC4P especially interesting is its specificity. Because its binding pocket has a particular size and shape, simple anions like fluoride or chloride fit quite snugly. However, when larger or more complex anions enter, like nitrate or formate, their shapes can disrupt the pocket structure, and the ions stick out into the surrounding solvent . At the same time, some ions bind strongly to omC4P even though they are relatively large, because they bind tightly to the NH groups.

Understanding these variations in binding is crucial for designing selective receptors. If a receptor can differentiate between closely related anions, it could help significantly in advancing applications such as water purification, medical diagnostics, or industrial sensing.

“These studies help us figure out what makes a receptor highly selective,” elaborates JILA graduate student Lane Terry, the papers’ first author. “If we can fine-tune its structure, we can create targeted ion sensors for real-world applications.”

The many different molecules trying to fill the binding site of octamethyl calix[4]pyrrole (omC4P). Image credit: Steven Burrows / JILA

First Step: Simple Halides

The team’s first study, published in The Journal of the American Chemical Society, focused on halide ions—fluoride, chloride, and bromide—with simple spherical shapes.

“We started with halides because they are the simplest—they act as just a single point charge,” Terry explains.

To analyze how these anions interacted with omC4P, researchers used cryogenic ion vibrational spectroscopy (CIVS) to take a molecular “snapshot” showing the interactions happening in the sample. CIVS is a technique that investigates ionized molecules cooled to low temperatures, which reduces their movement and isolates their vibrations. Ions are then bombarded with infrared photons, causing the ions to absorb specific wavelengths based on how their atoms are arranged and how they vibrate. This, in combination with quantum chemical calculations, allows researchers to measure how the receptor interacts with different ions without interference from external factors like solvent molecules.

After multiple CIVS measurements, the team verified their measurements with those predicted by Density Functional Theory (DFT), a computational method that calculates the molecular structure of complexes to predict how they interact.

“DFT helps us compare our experimental data with theoretical models,” Terry explains, “so we can confirm what we’re seeing and refine our understanding of ion binding.”

Through this process, the team discovered that fluoride formed the strongest hydrogen bonds, remaining tightly bound even in solution, whereas chloride and bromide showed weaker ion-receptor interactions due to weaker proton affinities and thus, more susceptible to solvent interaction.

“This is important because most of these ion receptors are used in aqueous environments,” Terry notes. “Meaning that fluoride’s binding will be more stable with these ion receptors than the other halides.”

Adding Complexity: Nitrate’s Unique Binding

Building on this foundation, the team then explored the nitrate anion binding to omC4P, detailed in The Journal of Physical Chemistry Letters. Unlike halides, nitrate is polyatomic, meaning it has multiple atoms, in this case, arranged in a Y-shape.

Using the CIVS plus DFT method, the researchers found that nitrate prefers a binding mode where only one of its three oxygen atoms interacts with the omC4P’s NH groups. This was a surprising result, as one might expect two oxygen atoms to bind symmetrically.

“Even though nitrate has multiple possible configurations, it strongly favors just one,” Terry says. “The ion shape and charge distribution make a big difference, especially when in an aqueous environment.”

The Most Complex Case: Formate and Isomerism

The final study, published in The Journal of Physical Chemistry B, tackled the most intricate binding behavior yet—formate (HCOO⁻), a small but more asymmetric anion binding to the omC4P. Unlike nitrate, formate was observed to have multiple binding configurations—a process known as isomerism—to the ion receptor.

"Formate actually isomerizes at a low enough energy that we detect multiple isomers, even at cryogenic temperatures,” Terry explains.

The researchers observed that the formate shifted between different configurations, unlike nitrate, which settled into one stable structure. Interestingly, the most stable formate configuration was not symmetrical at all, defying conventional expectations. While highly symmetrical structures often allow for predictable, in contrast, asymmetry can lead to unexpected behaviors that influence selectivity and stability in ion receptors.

After analyzing these findings, the team is now investigating modified omC4P with added structural “walls” to deepen the binding cavity and alter ion interactions, which will add further complexity to their experiment.

Beyond Fundamentals:

While these studies focus on fundamental chemistry, their implications extend far beyond the lab. Environmental monitoring, drug delivery, and chemical sensing all rely on understanding ion interactions at the molecular level.
Terry says, “We work closely with organic chemists who design these molecules. Our findings help them build better ion receptors with improved selectivity.”

Whether detecting contaminants in water or designing better drug carriers, their discoveries bring us one step closer to harnessing chemistry for the greater good.

This research was supported by the National Science Foundation, the JILA Physics Frontier Center, the University of Colorado Boulder, and Colorado State University.

Understanding how molecules interact with ions is a cornerstone of chemistry, with applications from pollution detection and cleanup to drug delivery. In a series of new studies led by JILA Fellow and University of Colorado Boulder chemistry professor Mathias Weber, researchers explored how a specific ion receptor called octamethyl calix[4]pyrrole (omC4P) binds to different anions, such as fluoride or nitrate. These findings provide fundamental insights about molecular binding that could help advance fields such as environmental science and synthetic chemistry.

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How to Bind with Metals and Water: A New Study on EDTA

Steven Burrows — Thu, 27 Jul 2023 17:30:53 +0000

How to Bind with Metals and Water: A New Study on EDTA Steven Burrows Thu, 07/27/2023 - 11:30

Kenna Hughes-Castleberry / JILA Science Communicator

The near-universal ability of EDTA to accommodate metal cations comes from its molecular flexibility, which allows it to respond to the chemical nature of the metal ion it binds. Image credit: Steven Burrows / JILA

Metal ions can be found in almost every environment, including wastewater, chemical waste and electronic recycling waste. Properly recovering and recycling valuable metals from various sources is crucial for sustainable resource management and contributes to environmental cleanup. Because of the scarcity of some of these metals, such as rare earth elements or nickel, scientists are working to find ways to remove these ions from the waste and recycle the metals. One method used to remove these metals is to bind them to other molecules known as chelators or chelating agents. Chelators have multiple molecular groups that combine to form binding sites with a natural affinity for binding metal ions, making them a natural choice to extract metals from toxic waste. Ethylenediaminetetraacetic acid, or EDTA, is a chelator commonly used in metal removal and many other applications, including medicine. “EDTA is used to treat heavy-metal poisoning,” JILA graduate student Lane Terry explained. “So, if you have lead poisoning, you can take EDTA, which binds to the lead and then safely passes through your system. It's also used as a food preservative. So EDTA is everywhere. It's in one of my topical creams, etc.” EDTA is also commonly used in various laboratories, including many within JILA.

To understand how EDTA binds to these metal ions and water molecules, Madison Foreman, a former JILA graduate student in the Weber group, now a postdoctoral researcher at the University of California, Berkeley, Terry, and their supervisor, JILA Fellow J. Mathias Weber, studied the geometry of the EDTA binding site using a unique method that helped to isolate the molecules and their bound ions, allowing for more in-depth analyses of the binding interactions. They published a series of three papers on this topic. In their first paper, published in the Journal of Physical Chemistry A, they found that the size of the metal ion changes where it sits in the EDTA binding site, which affects other binding interactions, especially with water.

Binding to Metal Ions

EDTA is a chemical commonly found in a chemistry or biology laboratory. “EDTA is employed in many different contexts,” explained Weber. “Whenever you want to get rid of a metal ion in a solution, you throw EDTA into the solution. EDTA will bind to pretty much any metal ion across the periodic table. That's what makes it so widely used in chemistry and biochemistry.” Because of this, EDTA as a model system can reveal more about similar binding behaviors in proteins, including some found in the human body. “People are using it as a model for the binding sites of metal ions in proteins,” said Weber.

However, actually observing the mechanics of EDTA binding is rather tricky. “So, to see exactly what’s going on, you must isolate your target complex from other species,” explained Weber. “That's why we bring these ions into the gas phase, where we can control the number of solvent molecules they interact with, first without any solvent, then selectively start adding solvent one molecule at a time to see what changes.” To do this, the EDTA ions were coaxed into a gas phase. “We then cool them in a cryogenic ion trap to about 50 Kelvin,” Foreman added. “After that, we attach weakly bound nitrogen molecules, which act as messengers telling us later that a photon has been absorbed. We only let those [tagged EDTA] molecules into the second half of the experiment. So there's nothing else, and we have only one sort of ion.”

These tagged ion clusters were then bombarded with light from a tunable laser, which helped detect the target clusters. “We hit that nitrogen-tagged EDTA complex with a photon, which ejects the nitrogen tag,” added Foreman. “So now we have these two fragments flying along, the complex ion and the nitrogen, as well as some amount of undissociated cluster that still has the nitrogen on it.” Thanks to this nitrogen eviction, the researchers can detect that light was absorbed. “After this, we do a second mass spectrometry step to distinguish the undissociated parent ions from the fragment ions,” Weber clarified. “We selectively only measure the intensity of those fragment ions as we tune our laser. That’s how we measure a photo-dissociation spectrum which is the analog of the infrared absorption spectrum of that complex.”

The infrared absorption spectrum of these complexes is something physicists and chemists often refer to, but because multiple atoms and molecules tend to contaminate a sample, this spectrum can be hard to isolate. With their gas-phase method, Weber and his team were able to create an analogous process to the infrared absorption measurements and understand more about the molecular behavior of EDTA. “Now, we can analyze the absorption features from that infrared spectrum to tell us something about the molecular structure,” added Weber. “So encoded in this infrared spectrum is how the EDTA molecule interacts with that metal ion, how its functional groups are oriented, and how that orientation changes as you attach water to it or bring it into solution.”

Binding to Water Molecules

As there is usually water around EDTA and proteins, as in the human body, Weber and his team were curious to understand how EDTA’s behavior changes when interacting with water. “These binding sites in proteins bind to metal ions like calcium or magnesium with similar functional groups as those in EDTA,” Weber explained. “And in proteins, the interaction between the metal ion and the protein binding pocket often does not allow lots of water molecules around it. Instead, it allows one or two in the vicinity. So, one could argue that the behavior of EDTA in the gas phase is actually a good model for trying to understand how these binding sites work.”

In one experiment, published in the Journal of Physical Chemistry Letters, the researchers added water to the metal-EDTA complex one molecule at a time to see how small amounts of water affected the EDTA. “Here you start with just the EDTA metal complex, and then you add one water molecule and see where it binds and how it deforms the metal-EDTA complex as a whole,” Weber added. “Then you can add the second water molecule and see how it influences the complex. In our research, we contrasted it with full solvation, full hydration.”

Studying how EDTA binds metals while in the presence of water can also help researchers better understand the binding processes happening within the human body. “One of the main proteins that EDTA is used to emulate is calmodulin, as its binding pockets are kind of similar,” Foreman explained. “Calmodulin is part of a larger class of proteins. They're all over the body serving all sorts of different functions. But the primary function of calmodulin is as a calcium mediator, so it reacts to the presence of calcium and signals other proteins to perform their functions. This can have effects on everything from hormones to muscle contraction.” Because calmodulin usually binds more to calcium than magnesium in water, the researchers wanted to see if EDTA mimicked this behavior in solution. “When we then look at EDTA, in solution, we see a similar trend in binding affinity, [where EDTA] would prefer to bind calcium than magnesium,” stated Foreman. “So then, by looking at it in the gas phase, or with just a few water molecules, we can see that the structure of the EDTA metal complex does change between magnesium and calcium. And that gives us a hint as to why these proteins might be more selective to some ions than others.”

Recycling Metal Ions

Weber and his team first studied how the molecule binds to alkaline earth metals (such as magnesium, calcium, strontium, or barium) to understand EDTA's interaction with different metal ions. In a second paper, published in 2023 in the Journal of Physical Chemistry A, the researchers found geometric differences in bindings between transition metals, like manganese, cobalt, and nickel, and alkaline earth metals, like calcium or magnesium. “The alkaline earth ions are simple ions. They present a spherically symmetric charge distribution to the outside world,” Weber elaborated. “So they're really round. The transition metals we published in the paper, their electronic structure brings directionality to their bonding with other molecules; they do not look like a spherically symmetric charge distribution. I usually phrase this where the alkaline earth metals are round and the transition metals are spiky. Their electronic structure produces “arms” or “spikes” in a structural template that allows other molecules to bind to them in a very structured way.”

Understanding how EDTA binds to various metals can give Weber and other scientists insight into using molecules that are similar to EDTA in wider applications, such as metal recycling. “Imagine nickel, cobalt, or rare earth metals, everything that you need for things from electric vehicles to batteries to your cell phone,” stated Weber. “These metals need to be removed from electronics waste during recycling; then they need to be purified. One way to do that is to grab them with something [like EDTA] …Lane gathered background information on using chelators for rare earth metal recycling. She actually wrote a proposal on that process. And there are other, very different kinds of ion receptors, too.” They’re hopeful that their results can help other scientists and engineers improve current metal chelation applications.

To understand how EDTA binds to metal ions and water molecules, Madison Foreman, a former JILA graduate student in the Weber group, now a postdoctoral researcher at the University of California, Berkeley, Terry, and their supervisor, JILA Fellow J. Mathias Weber, studied the geometry of the EDTA binding site using a unique method that helped to isolate the molecules and their bound ions, allowing for more in-depth analyses of the binding interactions. They published a series of three papers on this topic. In their first paper, published in the Journal of Physical Chemistry A, they found that the size of the metal ion changes where it sits in the EDTA binding site, which affects other binding interactions, especially with water.

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The Rules of Photon Thunderdome: For upconversion photoluminescence, four photons enter, one photon leaves

Steven Burrows — Mon, 05 Oct 2020 16:45:14 +0000

The Rules of Photon Thunderdome: For upconversion photoluminescence, four photons enter, one photon leaves Steven Burrows Mon, 10/05/2020 - 10:45

Rebecca Jacobson / JILA Science Communicator

Two triplet-state ions eliminate each other to create an excited singlet which fluoresces. Image credit: Steven Burrows / JILA

When it comes to photoluminescence, the rules for most materials are simple: shine a photon on the material, and one photon comes out. Other materials take some coaxing—shine two photons in and get a shorter wavelength photon out in a process called upconversion photoluminescence, or UCPL.

Many organic materials require a chemical sensitizer to get that upconversion photoluminescence—except for rubrene. This orange-tinted organic crystal can perform this upconversion photoluminescence process without an added sensitizer.

“The mystery was: why does this work for pure rubrene?” JILA Fellow Mathias Weber asked.

To answer this question, the Weber Group needed to learn the rules and the players for UCPL within the crystal. In their recently published study in the Journal of Physical Chemistry Letters, they found that this process plays out like “photon Thunderdome,” which could help scientists and engineers create new light sources and new technology that can harness the non-visible spectrum of light.

Photon Thunderdome

From earlier research, it was clear that UCPL is caused by a process called triplet-triplet annihilation, in which two particles with parallel spins combine, but at first it was not clear how the light was initially absorbed. Regular rubrene molecules don’t absorb near-infrared light.

Another weird behavior found in earlier research has to do with the number of incoming photons required to get one photon out. For simple photoluminescence, one needs one photon to go for one photon to go out. For triplet-triplet annihilation, two photons need to go in for one to come out. In rubrene, UCPL takes four photons.

Weber grinned as he summarized this as a molecular version of Thunderdome: “Two photons enter, one photon leaves. In rubrene, the rule of Thunderdome is four photons enter, one photon leaves.”

To get to the bottom of how UCPL in rubrene works, the Weber Group needed to learn exactly which wavelength of light caused this reaction, and what inside the crystal started the process. They scanned the wavelength of invisible near-infrared light they shone on a rubrene crystal, tuning their laser until they saw a flash of yellow light—a sign of UCPL. These near-infrared wavelengths told them what exactly started the UCPL process—positively-charged ions (called cations) and negatively-charged ions (called anions), probably on the crystal’s surface.

Two photons kick one cation and one anion into excited states. The cation and anion interact, combining their charges, and creating a rubrene molecule in its singlet ground state, and one in a triplet state. Another two photons achieve the same outcome with another pair of ions. The two triplets then combine, producing an excited singlet. That excited singlet fluoresces, and scientists see a blip of yellow light.

Now that the Weber Group knew that they needed a cation and an anion to get the process going, they could model it. In modeling the process, they were able to explain its other peculiar quality.

“The process needs four photons, so the output varies with the fourth power of the intensity of the incoming light. If you double the intensity of the incoming light, your output is sixteen times higher than before, and our model can account for that,” Weber said.

The ability to sustain UCPL is an interesting material property, because the photons released in upconverted photoluminescence have a higher energy than the photons that went in, Weber pointed out. In photovoltaics, upconversion can be used to convert low-energy photons that cannot directly generate electricity into higher-energy photons that can. Although pure rubrene doesn’t do this very efficiently, understanding this process could lead to better solar cells.

UCPL could also be used in relatively simple sensors in future quantum technology. For example, the process could be used to test the quality of novel light sources that produce “entangled light”, such as photon pairs rather than one photon at a time.

This study was published on August 10, 2020 in the Journal of Physical Chemistry Letters and was supported by the National Science Foundation’s Physics Frontier Center grant and the American Chemical Society Petroleum Research Fund.

The Weber Group has found what causes rubrene to generate upconversion photoluminescence. By exploring new routes to triplet formation and triplet-triplet annihilation, they learn how organic materials can take lower-energy photons and generate higher energy output, which could have implications for photovoltaics and new electronics.

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Leah Dodson Wins 2017 Miller Prize

Steven Burrows — Tue, 18 Jul 2017 21:00:12 +0000

Leah Dodson Wins 2017 Miller Prize Steven Burrows Tue, 07/18/2017 - 15:00

Julie Phillips / Science Communicator

Leah Dodson won the Miller Prize at the 72nd International Symposium on Molecular Spectroscopy, held June 19–23 in Urbana, Illinois. Dodson is an NRC postdoc whose official advisor is Jun Ye, but who primarily works on molecular spectroscopy in the Mathias Weber lab. Her award-winning talk was entitled “Oxalate Formation in Titanium––Carbon Dioxide Anionic Clusters Studied by Infrared Photodissociation Spectroscopy.”

“Leah gave a nice polished presentation with good organization and clarity,” said Ben McCall, Chair of the International Symposium on Molecular Spectroscopy, in a letter to Weber announcing the award. “She clearly outlined the rationale, the experiment, and the results. She was engaged, excited about her project, and good at thinking on the spot.”

Dodson’s project featured in her talk was the investigation of catalysts in model systems. Specifically, she studied the possible use of titanium dioxide (TiO₂) as a catalyst to break carbon-oxygen (C–O) bonds in carbon dioxide (CO₂) produced in a factory. Breaking C–O bonds in CO₂ is a key step in turning this greenhouse gas back into usable fuel––and keeping it out of the atmosphere. Dodson’s experiment worked surprisingly well. In the experiment, TiO₂ anions effectively broke CO₂molecules, forming metal carbonyl in the process. This experiment was the basis for her symposium talk, which resulted in the Miller Prize.

As a Miller Prize winner, Dodson has been invited to present a 15-min talk in one of the plenary sessions in the June 2018 symposium. Dodson will also serve as a judge in the 2018 Miller Prize competition. In addition, she and her coauthors have been invited to submit an article based on her talk at this year’s symposium to the Journal of Molecular Spectroscopy.

Leah Dodson won the Miller Prize at the 72nd International Symposium on Molecular Spectroscopy, held June 19–23 in Urbana, Illinois

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Recreating Fuels from Waste Gas

Steven Burrows — Mon, 21 Nov 2016 19:25:58 +0000

Recreating Fuels from Waste Gas Steven Burrows Mon, 11/21/2016 - 12:25

Julie Phillips / Science Communicator

Laser light knocks both neutral and charged bismuth atoms off a disk of bismuth metal. The negatively charged atoms then bind to a carbon dioxide (CO₂) molecule, and an electron is transferred to the CO₂ molecule from the metal. However, as more and more CO₂ molecules are added, two CO₂ molecules will bind to a single metal atom and form a carbon-carbon bond, creating an oxalate molecule, which steals more negative charge from the bismuth atom. Image credit: Steven Burrows / JILA

Graduate student Mike Thompson of the Weber group wants to understand the basic science of taking carbon dioxide (CO₂) produced by burning fossil fuels and converting it back into useful fuels. People could then use these fuels to generate electricity, heat homes and office buildings, power automobiles and trains, fly airplanes, and drive the industrial processes of modern life.

However, the conversion of CO₂ into useful fuels is a challenging problem in chemistry and chemical engineering. It takes energy to turn CO₂ into carbon monoxide (CO) and CO into natural gas (methane) and liquid fuels such as gasoline. The good news is that methods using electrochemical cells to transform CO₂ into CO could easily be powered by renewable energy from intermittent resources such as the Sun and the wind. Instead of adding more and more CO₂ from fossil fuels to the atmosphere, people could recycle CO₂from burning fossil fuels using electrochemical cells and alleviate the progression of global warming.

The trick is figuring out how to lower the amount of energy needed for turning CO₂ into CO. Without chemical tricks, the energy cost turns out to be way too high to be economical yet. The trick that’s needed is to use a catalyst. A catalyst is a metal or other substance that accelerates a chemical reaction without being affected.

Fortunately, electrodes made of metals such as gold, silver, or bismuth can catalyze the transformation of CO₂ to CO. Bismuth has advantages over other metals, including (1) working as well, if not better, than gold, (2) being readily available in large quantities because it is a by-product of lead mining, and (3) costing nearly 350 times less than gold per gram. Because of these advantages, bismuth metal is under consideration for CO₂conversion, but the molecular details of the process are not well understood. To gain a deeper insight into the process, the group recently began investigating the use of bismuth metal in CO₂ conversion catalysis on the molecular level.

The first step was acquiring a disk of bismuth that could be used to produce bismuth atoms. A trip to see Hans Green in JILA’s instrument shop resulted in the discovery of some 20-year-old, high-purity bismuth shot (1–2 cm pieces of pure metal). Green added the shot to a tailor-made disk-shaped aluminum mold and heated it up on a hot plate. After the disk cooled, Green machined it to provide a smooth surface to make it possible for the laser beam to blow off atoms one by one.

The second step was to begin a study of the chemistry of CO₂ conversion by looking at how to transfer an extra electron to a CO₂molecule. This step costs a lot of energy unless a catalyst is used.

“We study how a few CO₂ molecules bind to a single charged bismuth atom,” Thompson explained. “The reason we do this is that actual electrochemical cells are very complex systems, so we’re trying to simplify the system as much as possible so we can get at the heart of the interaction.”

What Thompson and his colleagues learned from studying their bismuth-CO₂ cluster model system was that a CO₂ molecule docked onto a negatively charged bismuth atom through the carbon atom. The chemical bond between the bismuth atom and the CO₂then allows an electron to spend about 65% of its time on the CO₂ molecule. By the time the researchers positioned approximately four CO₂ molecules around the bismuth–CO₂molecule, the extra electron was almost completely transferred to the attached CO₂molecule.

But when a fifth CO₂ molecule was added, suddenly two CO₂ molecules bound to the metal atom. The two CO₂ molecules also formed a carbon–carbon bond with each other, forming a molecule called oxalate. This is similar to processes in a real electrochemical cell, where oxalate can also be formed. This is a significant finding because it shows that the Weber group’s cluster model can be used to learn something about processes in electrochemical cells. And, with some additional work, there’s a good chance this model system will also produce CO!

The researchers responsible for this intriguing work include graduate student Michael Thompson, Fellow Mathias Weber, and group collaborator Jacob Ramsay (University of Aarhus, Denmark).

Graduate student Mike Thompson of the Weber group wants to understand the basic science of taking carbon dioxide (CO2) produced by burning fossil fuels and converting it back into useful fuels. People could then use these fuels to generate electricity, heat homes and office buildings, power automobiles and trains, fly airplanes, and drive the industrial processes of modern life.

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