Last year, the world emitted more than 37 billion metric tons of carbon dioxide, setting a new record high. As a result, sucking CO₂ out of the atmosphere has become an increasingly popular idea. Governments worldwide are banking on this technology, called direct air capture, to help them achieve climate goals and avoid the worst consequences of climate change.

But despite more than a dozen direct air capture facilities being up and running around the globe already, the technology still faces major technological hurdles — including its own high energy use.

In a study published May 1 in the journal ACS Energy Letters, researchers at the University of Colorado Boulder and collaborators revealed that a popular approach many engineers are exploring to reduce those energy costs would, in reality, fail. The team, including scientists at the National Renewable Energy Laboratory in Golden, Colorado and Delft University of Technology in the Netherlands, also proposed an alternative, more sustainable design for capturing CO₂ and converting it to fuels.

“Ideally, we want to take CO₂ out of the air and keep it out of the air,” said first author Hussain Almajed, a Ph.D. student in the Department of Chemical and Biological Engineering. “However, some of this CO₂ can be recycled into useful carbon-containing products, which is why researchers have proposed different ideas of how we can achieve that. Some of these ideas look very simple and elegant on paper, but researchers rarely check whether they are practical and economical in industrial settings.”

Trapping the gas

One of the most common direct air capture approaches is to use air contactors, essentially huge fans that pull air into a chamber filled with a basic liquid. CO₂ is acidic, so it naturally binds to and reacts with the solution to form harmless carbonate (the main ingredient in concrete) or bicarbonate (the ingredient in baking soda).

Stratos, one of the world’s largest direct air capture facilities under construction in Texas, uses this approach.

Once CO₂ is trapped in the carbonate or bicarbonate solutions, engineers must separate it out from the liquid so the liquid can return to the chamber to capture more CO₂.

Meanwhile, the captured carbon can be converted into things like plastics, carbonated drinks and even — with further processing — fuel to power homes and potentially airplanes.

But there is a catch. To release the trapped CO₂, companies need to heat the carbonate and bicarbonate solution to at least 900?C (1,652° F), a temperature solar and wind energy is unable to achieve. This step is usually powered by burning fossil-based fuels like natural gas or pure methane.

“If we have to release CO₂ in order to capture CO₂, it defeats the whole purpose of carbon capture,” said Wilson Smith, a professor in the Department of Chemical and Biological Engineering and a fellow of the Renewable and Sustainable Energy Institute at CU Boulder.

Close the loop

Researchers are actively looking for answers. One idea, commonly known as reactive capture, is to apply electricity to the carbonate and bicarbonate solutions, zapping the CO₂ and basic liquid apart in the chamber. In theory, the recycled liquid can then capture more CO₂, forming a closed-loop system.

“Reactive capture is now the buzzword in the field, and researchers proposed that it could help save energy and costs associated with carbon capture. But no one really assessed whether that’s realistic under industrial conditions,” Almajed said.

To do that, the team calculated the mass and energy outputs of the reactive capture units, based on given inputs, to understand how well the overall system would perform. They found that in an industrial setting, electricity would not be able to regenerate the basic liquid to re-capture more CO₂ from the air.

In fact, after five cycles of carbon capture and regeneration, the basic liquid could barely pull any CO₂ out of the air.

The team also suggested a tweak to the reactive capture process by adding a step called electrodialysis. The process splits additional water into acidic and basic ions, helping to maintain the basic liquid’s ability to absorb more CO₂. Electrodialysis can run on renewable electricity, making it a potentially sustainable way to turn captured CO₂ into useful products.

More importantly, electrodialysis can release CO₂ gas, which engineers can use to strengthen concrete.

“To me, turning CO₂ into rocks has to be one of the leading solutions to keep it out of the air over long periods of time,” Smith said. Concrete production is energy-intensive and responsible for 8% of global carbon emissions.

“This is solving multiple problems with one technology,” he said.

The root of the problem

According to the Intergovernmental Panel on Climate Change (IPCC), a team of scientists convened by the United Nations, carbon dioxide removal “is required to achieve global and national targets of net zero CO₂ and greenhouse gas emissions.”

Across the world, more than 20 direct air capture plants are in operation with 130 more currently under construction.

But Smith stresses that while carbon capture may have its place, cutting emissions is still the most critical step needed to avoid the worst outcomes of climate change.

“Imagining Earth as a bathtub, with the running water from the faucet being CO₂. The bathtub is getting full and becoming unlivable. Now, we have two options. We can use a little cup to scoop out the water, cup by cup, or we can turn the faucet off,” Smith said.

“Cutting emissions has to be the priority.”

When it comes to muscles and muscle disorders, the importance of a discovery like this cannot be overstated.

The muscle of muscles

The very core function of life — breathing — is controlled by your skeletal muscles, as is regulation of whole-body metabolism and every movement you make:

• And even blinking

In context

Skeletal muscles are formed during embryonic development by the fusion of hundreds of specialized cells called myoblasts. Adult skeletal muscles maintain regenerative capacity, which is attributed to the presence of muscle stem cells, named satellite cells.

After injury, satellite cells undergo several rounds of proliferation followed by their differentiation into myoblasts. These myoblasts once again fuse with each other and to injured myofibers to accomplish muscle regeneration.

In many muscular disorders, this intrinsic capacity of muscles to regenerate is diminished resulting in the loss of muscle mass and function.

The science

UH researchers found that Inositol-requiring enzyme 1, a key signaling protein, is essential for myoblast fusion during muscle formation and growth.

“During muscle regeneration, IRE1 augments the activity of X-box binding protein 1 which in turn stimulates the gene expression of multiple transmembrane proteins required for myoblast fusion,” reports Ashok Kumar, Else and Philip Hargrove Endowed Professor of pharmacy in the Department of Pharmacological and Pharmaceutical Sciences at the UH College of Pharmacy, in EMBO Reports.

According to researchers, increasing the levels of IRE1 or XBP1 in muscle stem cells outside the body, followed by their injection in patients’ muscle tissues will improve muscle repair and reduce the severity of disease.

“We also found that augmenting the levels of IRE1α or XBP1 in myoblasts leads to the formation of myotubes (muscle cells) having an increased diameter,” said Kumar.

That increase in diameter can be significant.

“Size is very important for muscle. Muscle grows only in size, not in number,” said Aniket Joshi, a graduate student in Kumar’s lab and first author on the article. “Muscular people have larger muscle cells. Larger muscles generally work better- can lift more weight, run and walk faster, and improve overall metabolism of the body and prevent various diseases, such as type II diabetes.”

Flexing their muscles

This new research is not the first flex for Kumar’s team. In 2021, research from Kumar’s lab published in the ELife journal described the role of the IRE1α/XBP1 signaling axis in regeneration of healthy skeletal muscle after acute injury and in models of Duchenne Muscular Dystrophy. In this study, they found that IRE1α/XBP1 signaling axis also plays an important cell autonomous role in satellite cells.

Along with Kumar and Joshi, post-doctoral fellow Meiricris Tomaz da Silva and research assistant professor, Anirban Roy conducted the research in Kumar’s lab. Other authors on the article from the University of Houston include Micah Castillo, Preethi Gunaratne, Mingfu Wu, Yu Liu, and a former post-doctoral fellow in Kumar’s lab Tatiana E. Koike along with Takao Iwawaki of Kanazawa Medical University, Japan.

The work is led by Dr. Mengying Liu from Washington and Lee University in collaboration with researchers at Texas A&M University. The team investigated formation of cracks in initially flawless, crack-free samples of a nickel-base alloy (Inconel 725), which is primarily known for its strength and corrosion resistance. There are currently several working hypotheses that attempt to explain hydrogen embrittlement. The results of this study show that one of the more well-known hypotheses — hydrogen enhanced localized plasticity (HELP) — is not applicable in the case of this alloy.

Plasticity, or irreversible deformation, is not uniform throughout a material, but is instead localized to certain points. HELP hypothesizes that cracks initiate at the points with the highest localized plasticity.

“As far as I know, ours is the first study that actually looks in real time to see where cracks initiate — and isn’t at locations of highest localized plasticity,” said co-author Dr. Michael J. Demkowicz, a professor in the Department of Materials Science and Engineering at Texas A&M University and Liu’s PhD advisor. “Our study tracks both the localized plasticity and the crack initiation locations in real time.”

Tracking crack initiation in real time is crucial. When examining a sample after a crack has appeared, the hydrogen has already escaped from the material, making it impossible to understand the mechanism that led to the damage.

“Hydrogen easily escapes from metals, so you can’t figure out what it does to embrittle a metal by examining specimens after they’ve been tested. You have to look while you’re testing,” said Demkowicz.

This study helps to lay the groundwork for better predictions of hydrogen embrittlement. In the future, hydrogen may replace fossil fuels as a clean energy source. If this change occurs, all of the infrastructure currently used to store and use fossil fuels would become susceptible to hydrogen embrittlement. Predicting embrittlement is crucial for preventing unexpected failures, making a future hydrogen economy possible.

The experiments for this study, as well as the preliminary data analysis, were conducted at Texas A&M, with Liu providing further data analysis and manuscript preparation at Washington and Lee. This paper is co-authored by Liu, Demkowicz and Texas A&M doctoral student Lai Jiang.

University of Illinois Urbana-Champaign chemical and biomolecular engineering professor Simon Rogers and graduate student Krutarth Kamani specialize in determining how soft materials yield to stress and have shown how solid and liquid physical states can exist together in the same material. This area is of high interest due to its importance to industrial, environmental and biomedical applications.

Along the way, the team identified a communication breakdown among the scientists who work in this area, causing a bottleneck between a theoretical understanding of soft material behavior and real-world applications.

When soft materials — natural or synthetic — deform under pressure, they eventually reach a critical point where they either return to their original form or undergo permanent deformation, like stretching or breaking a piece of elastic. This process is known as yielding. A gradual yielding transition is termed ductile behavior, while an abrupt one is referred to as brittle behavior, the researchers said.

“At a recent conference, we realized that all of us who study soft materials from all over Europe and North America couldn’t agree what the connection is between brittle and ductile behavior nor how to define it.”

In the study, published in the Proceedings of the National Academy of Sciences, instead of viewing soft material behavior as one or the other — brittle or ductile — Rogers’ team considers a spectrum of yielding behaviors. This allowed the team to build a continuum model, which led to them uncovering the brittility factor. This factor is critical in determining how and why soft materials fail.

Essentially, brittility affects how a material deforms permanently under stress. The team’s model indicates that the higher the brittility factor, the less a soft material will deform permanently before yielding.

As in the team’s past studies, the model was developed and tested using data from numerous experiments that subjected various soft materials to stress while measuring the individual strain responses using a device called a rheometer.

“We didn’t expect this study to explain as much as it does,” said Rogers, who is also an affiliate at the Beckman Institute for Advanced Science and Technology at the U. of. I. “What we ended up with was a way to bring a whole bunch of soft material behaviors together under the same physics umbrella. Previously, they’d been studied independently or maybe all been applied simultaneously, but never thought of as being physically or mathematically connected.”

This finding will allow researchers to explain precisely why some materials are more resistant to rapid yielding than others, a question that has eluded researchers for decades.

“This single parameter amazingly connects so many puzzling observations researchers have come across over the years,” Kamani said.

“This work marks the point at which we are approaching the crest of the hill in understanding soft materials behavior,” Rogers said. “We’ve always felt like each step takes us higher, but with no end in sight. Now we can see the top of the hill, and we are closer to the top and free to move forward in whatever direction we would like.”

The National Science Foundation supported this research.

Although adaptive radar systems have been around since World War II, they’ve hit a fundamental performance wall in the past couple of decades. But with the help of modern AI approaches and lessons learned from computer vision, researchers at Duke University have broken through that wall, and they want to bring everyone else in the field along with them.

In a new paper published July 16 in the journal IET Radar, Sonar & Navigation, Duke engineers show that using convolutional neural networks (CNNs) — a type of AI that revolutionized computer vision — can greatly enhance modern adaptive radar systems. And in a move that parallels the impetus of the computer vision boom, they have released a large dataset of digital landscapes for other AI researchers to build on their work.

“Classical radar methods are very good, but they aren’t good enough to meet industry demands for products such as autonomous vehicles,” said Shyam Venkatasubramanian, a graduate research assistant working in the lab of Vahid Tarokh, the Rhodes Family Professor of Electrical and Computer Engineering at Duke. “We’re working to bring AI into the adaptive radar space to tackle problems like object detection, localization and tracking that industry needs solved.”

At its most basic level, radar is not difficult to understand. A pulse of high-frequency radio waves is broadcast, and an antenna gathers data from any waves that bounce back. As technology has advanced, however, so too have the concepts used by modern radar systems. With the ability to shape and direct signals, process multiple contacts at once, and filter out background noise, the technology has come a long way in the past century.

But radar has come just about as far as it can using these techniques alone. Adaptive radar systems still struggle to accurately localize and track moving objects, especially in complex environments like mountainous terrain.

To move adaptive radar into the age of AI, Venkatasubramanian and Tarokh were inspired by the history of computer vision. In 2010, researchers at Stanford University released an enormous image database consisting of over 14 million annotated images called ImageNet. Researchers around the world used ImageNet to test and compare new AI approaches that became industry standard.

In the new paper, Venkatasubramanian and his collaborators show that using the same AI approaches greatly improves the performance of current adaptive radar systems.

“Our research parallels the research of the earliest users of AI in computer vision and the creators of ImageNet, but within adaptive radar,” Venkatasubramanian said. “Our proposed AI takes as input processed radar data and outputs a prediction of the target’s location through a simple architecture that can be thought of as paralleling the predecessor of most modern computer vision architectures.”

While the group has yet to test their methods in the field, they benchmarked their AI’s performance on a modeling and simulation tool called RFView®, which gains its accuracy by incorporating the Earth’s topography and terrain into its modeling toolbox. Then, continuing in the footsteps of computer vision, they created 100 airborne radar scenarios based on landscapes from across the contiguous United States and released it as an open-source asset called “RASPNet.”

This is a valuable asset, as only a handful of teams have access to RFView®. The researchers, however, received special permission from the creators of RFView® to build the dataset — which contains more than 16 terabytes of data built over the course of several months — and make it publicly available.

“I am delighted that this groundbreaking work has been published, and particularly that the associated data is being made available in the RASPNet repository,” said Hugh Griffiths, Fellow Royal Academy of Engineering, Fellow IEEE, Fellow IET, OBE, and the THALES/Royal Academy Chair of RF Sensors at University College London, who was not involved with the work. “This will undoubtedly stimulate further work in this important area, and ensure that the results can readily be compared with each other.”

The scenarios included were handpicked by radar and machine learning experts and have a wide range of geographical complexity. On the easiest side for adaptive radar systems to handle is the Bonneville Salt Flats, while the hardest is Mount Rainier. Venkatasubramanian and his group hope that others will take their ideas and dataset and build even better AI approaches.

For example, in a previous paper, Venkatasubramanian showed that an AI tailored to a specific geographical location could achieve up to a seven-fold improvement in localizing objects over classical methods. If an AI could select a scenario on which it had already been trained that is similar to its current environment, it should substantially improve in performance.

“We think this will have a really big impact on the adaptive radar community,” Venkatasubramanian said. “As we move forward and continue adding capabilities to the dataset, we want to provide the community with everything it needs to push the field forward into using AI.”

This work was supported by the Air Force Office of Scientific Research (FA9550-21-1-0235, 20RYCORO51, 20RYCOR052).

The research group of corresponding author Laure Kayser, assistant professor in the Department of Materials Science and Engineering in UD’s College of Engineering with a joint appointment in the Department of Chemistry and Biochemistry in the College of Arts and Sciences, regularly works with PEDOT:PSS, a polymer that has both electronic and ionic conductivity, and was interested in finding ways to synthesize this material from plastic waste.

After connecting with Argonne chemist David Kaphan during an event hosted by UD’s research office, the research teams at UD and Argonne began evaluating the hypothesis that PEDOT:PSS could be made by sulfonating polystyrene, a synthetic plastic found in many types of disposable containers and packing materials.

Sulfonation is a common chemical reaction where a hydrogen atom is replaced by sulfonic acid; the process is used to create a variety of products such as dyes, drugs and ion exchange resins. These reactions can either be “hard” (with higher conversion efficiency but that require caustic reagents) or “soft” (a less efficient method but one that uses milder materials).

In this paper, the researchers wanted to find something in the middle: “A reagent that is efficient enough to get really high degrees of functionalization but that doesn’t mess up your polymer chain,” Kayser explained.

The researchers first turned to a method described in a previous study for sulfonating small molecules, one that showed promising results in terms of efficiency and yield, using 1,3-Disulfonic acid imidazolium chloride ([Dsim]Cl). But adding functional groups onto a polymer is more challenging than for a small molecule, the researchers explained, because not only are unwanted byproducts harder to separate, any small errors in the polymer chain can change its overall properties.

To address this challenge, the researchers embarked on many months of trial and error to find the optimal conditions that minimized side reactions, said Kelsey Koutsoukos, a materials science doctoral candidate and second author of this paper.

“We screened different organic solvents, different molar ratios of the sulfonating agent, and evaluated different temperatures and times to see which conditions were the best for achieving high degrees of sulfonation,” he said.

The researchers were able to find reaction conditions that resulted in high polymer sulfonation, minimal defects and high efficiency, all while using a mild sulfonating agent. And because the researchers were able to use polystyrene, specifically waste Styrofoam, as a starting material, their method also represents an efficient way to convert plastic waste into PEDOT:PSS.

Once the researchers had PEDOT:PSS in hand, they were able to compare how their waste-derived polymer performed compared to commercially available PEDOT:PSS.

“In this paper, we looked at two devices — an organic electronic transistor and a solar cell,” said Chun-Yuan Lo, a chemistry doctoral candidate and the paper’s first author. “The performance of both types of conductive polymers was comparable, and shows that our method is a very eco-friendly approach for converting polystyrene waste into high-value electronic materials.”

Specific analyses conducted at UD included X-ray photoelectron spectroscopy (XPS) at the surface analysis facility, film thickness analysis at the UD Nanofabrication Facility, and solar cell evaluation at the Institute of Energy Conversion. Argonne’s advanced spectroscopy equipment, such as carbon NMR, was used for detailed polymer characterization. Additional support was provided by materials science and engineering professor Robert Opila for solar cell analysis and by David C. Martin, the Karl W. and Renate Böer Chaired Professor of Materials Science and Engineering, for the electronic device performance analyses.

One unexpected finding related to the chemistry, the researchers added, is the ability to use stoichiometric ratios during the reaction.

“Typically, for sulfonation of polystyrene, you have to use an excess of really harsh reagents. Here, being able to use a stoichiometric ratio means that we can minimize the amount of waste being generated,” Koutsoukos said.

This finding is something the Kayser group will be looking into further as a way to “fine-tune” the degree of sulfonation. So far, they’ve found that by varying the ratio of starting materials, they can change the degree of sulfonation on the polymer. Along with studying how this degree of sulfonation impacts the electrical properties of PEDOT:PSS, the team is interested in seeing how this fine-tuning capability can be used for other applications, such as fuel cells or water filtration devices, where the degree of sulfonation greatly impacts a material’s properties.

“For the electronic devices community, the key takeaway is that you can make electronic materials from trash, and they perform just as well as what you would purchase commercially,” Kayser said. “For the more traditional polymer scientists, the fact that you can very efficiently and precisely control the degree of sulfonation is going to be of interest to a lot of different communities and applications.”

The researchers also see great potential for how this research can contribute to ongoing global sustainability efforts by providing a new way to convert waste products into value-added materials.

“Many scientists and researchers are working hard on upcycling and recycling efforts, either by chemical or mechanical means, and our study provides another example of how we can address this challenge,” Lo said.

The complete list of co-authors includes Chun-Yuan Lo, Kelsey Koutsoukos, Dan My Nguyen, Yuhang Wu, David Angel Trujillo, Tulaja Shrestha, Ethan Mackey, Vidhika Damani, Robert Opila, David Martin, and Laure Kayser from the University of Delaware and Tabitha Miller, Uddhav Kanbur, and David Kaphan from Argonne National Laboratory.