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    A mineral produced by plate tectonics has a global cooling effect, study finds

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    MIT geologists have found that a clay mineral on the seafloor, called smectite, has a surprisingly powerful ability to sequester carbon over millions of years.

    Under a microscope, a single grain of the clay resembles the folds of an accordion. These folds are known to be effective traps for organic carbon.

    Now, the MIT team has shown that the carbon-trapping clays are a product of plate tectonics: When oceanic crust crushes against a continental plate, it can bring rocks to the surface that, over time, can weather into minerals including smectite. Eventually, the clay sediment settles back in the ocean, where the minerals trap bits of dead organisms in their microscopic folds. This keeps the organic carbon from being consumed by microbes and expelled back into the atmosphere as carbon dioxide.

    Over millions of years, smectite can have a global effect, helping to cool the entire planet. Through a series of analyses, the researchers showed that smectite was likely produced after several major tectonic events over the last 500 million years. During each tectonic event, the clays trapped enough carbon to cool the Earth and induce the subsequent ice age.

    The findings are the first to show that plate tectonics can trigger ice ages through the production of carbon-trapping smectite.

    These clays can be found in certain tectonically active regions today, and the scientists believe that smectite continues to sequester carbon, providing a natural, albeit slow-acting, buffer against humans’ climate-warming activities.

    “The influence of these unassuming clay minerals has wide-ranging implications for the habitability of planets,” says Joshua Murray, a graduate student in MIT’s Department of Earth, Atmospheric, and Planetary Sciences. “There may even be a modern application for these clays in offsetting some of the carbon that humanity has placed into the atmosphere.”

    Murray and Oliver Jagoutz, professor of geology at MIT, have published their findings today in Nature Geoscience.

    A clear and present clay

    The new study follows up on the team’s previous work, which showed that each of the Earth’s major ice ages was likely triggered by a tectonic event in the tropics. The researchers found that each of these tectonic events exposed ocean rocks called ophiolites to the atmosphere. They put forth the idea that, when a tectonic collision occurs in a tropical region, ophiolites can undergo certain weathering effects, such as exposure to wind, rain, and chemical interactions, that transform the rocks into various minerals, including clays.

    “Those clay minerals, depending on the kinds you create, influence the climate in different ways,” Murray explains.

    At the time, it was unclear which minerals could come out of this weathering effect, and whether and how these minerals could directly contribute to cooling the planet. So, while it appeared there was a link between plate tectonics and ice ages, the exact mechanism by which one could trigger the other was still in question.

    With the new study, the team looked to see whether their proposed tectonic tropical weathering process would produce carbon-trapping minerals, and in quantities that would be sufficient to trigger a global ice age.

    The team first looked through the geologic literature and compiled data on the ways in which major magmatic minerals weather over time, and on the types of clay minerals this weathering can produce. They then worked these measurements into a weathering simulation of different rock types that are known to be exposed in tectonic collisions.

    “Then we look at what happens to these rock types when they break down due to weathering and the influence of a tropical environment, and what minerals form as a result,” Jagoutz says.

    Next, they plugged each weathered, “end-product” mineral into a simulation of the Earth’s carbon cycle to see what effect a given mineral might have, either in interacting with organic carbon, such as bits of dead organisms, or with inorganic, in the form of carbon dioxide in the atmosphere.

    From these analyses, one mineral had a clear presence and effect: smectite. Not only was the clay a naturally weathered product of tropical tectonics, it was also highly effective at trapping organic carbon. In theory, smectite seemed like a solid connection between tectonics and ice ages.

    But were enough of the clays actually present to trigger the previous four ice ages? Ideally, researchers should confirm this by finding smectite in ancient rock layers dating back to each global cooling period.

    “Unfortunately, as clays are buried by other sediments, they get cooked a bit, so we can’t measure them directly,” Murray says. “But we can look for their fingerprints.”

    A slow build

    The team reasoned that, as smectites are a product of ophiolites, these ocean rocks also bear characteristic elements such as nickel and chromium, which would be preserved in ancient sediments. If smectites were present in the past, nickel and chromium should be as well.

    To test this idea, the team looked through a database containing thousands of oceanic sedimentary rocks that were deposited over the last 500 million years. Over this time period, the Earth experienced four separate ice ages. Looking at rocks around each of these periods, the researchers observed large spikes of nickel and chromium, and inferred from this that smectite must also have been present.

    By their estimates, the clay mineral could have increased the preservation of organic carbon by less than one-tenth of a percent. In absolute terms, this is a miniscule amount. But over millions of years, they calculated that the clay’s accumulated, sequestered carbon was enough to trigger each of the four major ice ages.

    “We found that you really don’t need much of this material to have a huge effect on the climate,” Jagoutz says.

    “These clays also have probably contributed some of the Earth’s cooling in the last 3 to 5 million years, before humans got involved,” Murray adds. “In the absence of humans, these clays are probably making a difference to the climate. It’s just such a slow process.”

    “Jagoutz and Murray’s work is a nice demonstration of how important it is to consider all biotic and physical components of the global carbon cycle,” says Lee Kump, a professor of geosciences at Penn State University, who was not involved with the study. “Feedbacks among all these components control atmospheric greenhouse gas concentrations on all time scales, from the annual rise and fall of atmospheric carbon dioxide levels to the swings from icehouse to greenhouse over millions of years.”

    Could smectites be harnessed intentionally to further bring down the world’s carbon emissions? Murray sees some potential, for instance to shore up carbon reservoirs such as regions of permafrost. Warming temperatures are predicted to melt permafrost and expose long-buried organic carbon. If smectites could be applied to these regions, the clays could prevent this exposed carbon from escaping into and further warming the atmosphere.

    “If you want to understand how nature works, you have to understand it on the mineral and grain scale,” Jagoutz says. “And this is also the way forward for us to find solutions for this climatic catastrophe. If you study these natural processes, there’s a good chance you will stumble on something that will be actually useful.”

    This research was funded, in part, by the National Science Foundation. More

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      in Environment

      Bringing the environment to the forefront of engineering

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      In a recent podcast interview with MIT President Sally Kornbluth, Associate Professor Desirée Plata described her childhood pastime of roaming the backyards and businesses of her grandmother’s hometown of Gray, Maine. Through her wanderings, Plata noticed a disturbing pattern.

      “I was 7 or 8 when I caught wind of all the illness,” Plata recalls. “It seemed like in every other house there was somebody who had a neurological disorder or a cancer of some sort.”

      While driving home one night with her mom, Plata made her first environmental hypothesis from the back seat. “I told my mom, ‘I think there’s something in the water or air where these people live.’”

      The conversation happened in the late 1980s. Plata was a little older when she learned her intuition was correct: The Environmental Protection Agency determined that a waste disposal facility had contaminated drinking water in the area while processing more than 1 million gallons of waste between 1965 and 1978.

      “There was a New York Times article on it, but it was sort of buried in a Sunday paper and a lot of folks up in Maine didn’t hear about it,” Plata says.

      What most struck Plata was that Gray was a tight-knit community, and the people who owned the waste disposal facility were friends with everybody. Eventually, some of the owner’s children even got sick.

      “People don’t poison their neighbors on purpose,” Plata says. “A lot of industrial contamination happens either by accident or because the engineers don’t know better. As an environmental scientist and engineer, it’s part of my job to help industrial engineers of any variety design their systems and processes such that they are thinking about what’s going into the environment from the start.”

      The insight led Plata to MIT, first as a PhD student, then as a visiting professor, and today as the newly tenured associate professor of civil and environmental engineering.

      These days Plata’s work is a bit more complex than her early backseat musings. In fact, her efforts extend far beyond research and include mentoring students, entrepreneurship, coalition-building, and coordination across industry, academia, and government. But the work can still be traced back to the childhood insight that environmental optimization needs to be a more tangible and important part of everyone’s thinking.

      “People think sustainability is this nebulous thing they can’t get their hands around,” Plata says. “But there are actually a set of rigorous principles you can use, and each one of those has a metric or a thing you can measure to go with it. MIT is such an innovative place. If we can incorporate environmental objectives into design at a place like MIT, the hope is the world can engage as well.”

      Taking the plunge

      Plata was first introduced to environmental research in high school, but it wasn’t until she attended Union College and got to work in a research lab that she knew it was what she’d do for the rest of her life.

      After graduating from Union, Plata decided to skip a master’s degree and “take the plunge” into the MIT-Woods Hole Oceanographic Institution (WHOI) joint doctoral program.

      “Talk about drinking from a firehose,” Plata says. “Everybody you bump into knows something that can help you solve the very hard problem you’re working on.”

      Plata began the program studying oil spills, and a paper she co-authored helped spur a law that changed the way oil is transported off the coast of Massachusetts. But developments in her personal life made her want to prevent environmental disasters before they happen.

      In her last year at Union, Plata’s aunt was diagnosed with breast cancer — a disease that’s been linked to one of the chemicals dumped in Gray, Maine. While Plata was at MIT, her aunt was receiving treatment at Massachusetts General Hospital down the road, so Plata would work at the lab at night, stay with her aunt during treatments all day, and go home with her on the weekends.

      “As I’m sampling oil, I’m recognizing that nothing I’m doing is going to help women like her escape the illness,” Plata recalls.

      In her third year of the MIT-WHOI program, Plata shifted her research to explore how industrial emissions generated during the creation of materials known as carbon nanotubes could inform how those valuable new materials were forming. The work led to a dramatically more sustainable way to make the materials, which are needed for important environmental applications themselves.

      After earning her PhD, Plata served as a visiting professor at MIT for two years before working in faculty positions at Duke University and Yale University, where she studied green chemistry and green optimization. She returned to MIT as an assistant professor in civil and environmental engineering in 2018.

      Working beyond academia

      While at Yale, Plata started a company, Nth Cycle, which uses electric currents to extract critical minerals like cobalt and nickel from lithium-ion batteries and other electronic waste. The company began commercial production last year.

      Plata also works extensively with government and industry, serving on a Massachusetts committee that published a roadmap to decarbonizing the state by 2050 and advising companies both formally and informally. (She estimates she gets a call every two weeks from a new company working on a sustainability problem.)

      “It’s undeniable that industry has an enormous impact on the environment,” Plata says. “Some like to think the government can wave a magic wand and make some regulation and we won’t be in this situation, but that’s not the case. There are technical challenges that need to be solved and businesses play an incredibly important role as agents of change.”

      Plata’s research at MIT, meanwhile, is focused increasingly on methane. Last year she helped create the MIT Methane Network, which she directs.

      Plata’s research has explored ways to convert methane into less harmful carbon dioxide and other fuels in places like dairy farms and coal plants. This past summer she took a team of students to dairy barns to conduct field tests.

      “If you could take methane from coal mining out of the air globally, it’s equivalent to taking all of the combustion engine vehicles off the road, even accounting for the small generation of CO2 that we have [as the result of our process],” Plata says. “If you can fix the problem at dairy farms, it’s like all the combustion engine vehicle emissions times three. It’s a hugely impactful number.”

      Taking action

      When Plata was in fourth grade, her teacher had students pick up trash around a nearby bay. She’s since done the exercise with other fourth graders.

      “You ask them what they think they’ll find, and they say, ‘Nothing. I didn’t see any trash on the way to school today,’ but when you ask them to look, everybody fills their bag by the end of the trip, and you start to realize how much fugitive emissions of waste exists, and then you start to start thinking about all of the chemical contamination that you can’t see,” Plata says.

      One of Plata’s chief research goals can be summed up with that exercise: getting people to appreciate the importance of environmental criteria and motivating them to take action.

      “Today, I see people looking for these silver bullet solutions to solve environmental problems,” Plata says. “That’s not how we got into this mess, and it’s not how we’re going to get out of it. The problem is really distributed, so what we really need is the sum of a lot of small actions to change the system.” More

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      in Energy

      Study suggests energy-efficient route to capturing and converting CO2

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      In the race to draw down greenhouse gas emissions around the world, scientists at MIT are looking to carbon-capture technologies to decarbonize the most stubborn industrial emitters.

      Steel, cement, and chemical manufacturing are especially difficult industries to decarbonize, as carbon and fossil fuels are inherent ingredients in their production. Technologies that can capture carbon emissions and convert them into forms that feed back into the production process could help to reduce the overall emissions from these “hard-to-abate” sectors.

      But thus far, experimental technologies that capture and convert carbon dioxide do so as two separate processes, that themselves require a huge amount of energy to run. The MIT team is looking to combine the two processes into one integrated and far more energy-efficient system that could potentially run on renewable energy to both capture and convert carbon dioxide from concentrated, industrial sources.

      In a study appearing today in ACS Catalysis, the researchers reveal the hidden functioning of how carbon dioxide can be both captured and converted through a single electrochemical process. The process involves using an electrode to attract carbon dioxide released from a sorbent, and to convert it into a reduced, reusable form.

      Others have reported similar demonstrations, but the mechanisms driving the electrochemical reaction have remained unclear. The MIT team carried out extensive experiments to determine that driver, and found that, in the end, it came down to the partial pressure of carbon dioxide. In other words, the more pure carbon dioxide that makes contact with the electrode, the more efficiently the electrode can capture and convert the molecule.

      Knowledge of this main driver, or “active species,” can help scientists tune and optimize similar electrochemical systems to efficiently capture and convert carbon dioxide in an integrated process.

      The study’s results imply that, while these electrochemical systems would probably not work for very dilute environments (for instance, to capture and convert carbon emissions directly from the air), they would be well-suited to the highly concentrated emissions generated by industrial processes, particularly those that have no obvious renewable alternative.

      “We can and should switch to renewables for electricity production. But deeply decarbonizing industries like cement or steel production is challenging and will take a longer time,” says study author Betar Gallant, the Class of 1922 Career Development Associate Professor at MIT. “Even if we get rid of all our power plants, we need some solutions to deal with the emissions from other industries in the shorter term, before we can fully decarbonize them. That’s where we see a sweet spot, where something like this system could fit.”

      The study’s MIT co-authors are lead author and postdoc Graham Leverick and graduate student Elizabeth Bernhardt, along with Aisyah Illyani Ismail, Jun Hui Law, Arif Arifutzzaman, and Mohamed Kheireddine Aroua of Sunway University in Malaysia.

      Breaking bonds

      Carbon-capture technologies are designed to capture emissions, or “flue gas,” from the smokestacks of power plants and manufacturing facilities. This is done primarily using large retrofits to funnel emissions into chambers filled with a “capture” solution — a mix of amines, or ammonia-based compounds, that chemically bind with carbon dioxide, producing a stable form that can be separated out from the rest of the flue gas.

      High temperatures are then applied, typically in the form of fossil-fuel-generated steam, to release the captured carbon dioxide from its amine bond. In its pure form, the gas can then be pumped into storage tanks or underground, mineralized, or further converted into chemicals or fuels.

      “Carbon capture is a mature technology, in that the chemistry has been known for about 100 years, but it requires really large installations, and is quite expensive and energy-intensive to run,” Gallant notes. “What we want are technologies that are more modular and flexible and can be adapted to more diverse sources of carbon dioxide. Electrochemical systems can help to address that.”

      Her group at MIT is developing an electrochemical system that both recovers the captured carbon dioxide and converts it into a reduced, usable product. Such an integrated system, rather than a decoupled one, she says, could be entirely powered with renewable electricity rather than fossil-fuel-derived steam.

      Their concept centers on an electrode that would fit into existing chambers of carbon-capture solutions. When a voltage is applied to the electrode, electrons flow onto the reactive form of carbon dioxide and convert it to a product using protons supplied from water. This makes the sorbent available to bind more carbon dioxide, rather than using steam to do the same.

      Gallant previously demonstrated this electrochemical process could work to capture and convert carbon dioxide into a solid carbonate form.

      “We showed that this electrochemical process was feasible in very early concepts,” she says. “Since then, there have been other studies focused on using this process to attempt to produce useful chemicals and fuels. But there’s been inconsistent explanations of how these reactions work, under the hood.”

      Solo CO2

      In the new study, the MIT team took a magnifying glass under the hood to tease out the specific reactions driving the electrochemical process. In the lab, they generated amine solutions that resemble the industrial capture solutions used to extract carbon dioxide from flue gas. They methodically altered various properties of each solution, such as the pH, concentration, and type of amine, then ran each solution past an electrode made from silver — a metal that is widely used in electrolysis studies and known to efficiently convert carbon dioxide to carbon monoxide. They then measured the concentration of carbon monoxide that was converted at the end of the reaction, and compared this number against that of every other solution they tested, to see which parameter had the most influence on how much carbon monoxide was produced.

      In the end, they found that what mattered most was not the type of amine used to initially capture carbon dioxide, as many have suspected. Instead, it was the concentration of solo, free-floating carbon dioxide molecules, which avoided bonding with amines but were nevertheless present in the solution. This “solo-CO2” determined the concentration of carbon monoxide that was ultimately produced.

      “We found that it’s easier to react this ‘solo’ CO2, as compared to CO2 that has been captured by the amine,” Leverick offers. “This tells future researchers that this process could be feasible for industrial streams, where high concentrations of carbon dioxide could efficiently be captured and converted into useful chemicals and fuels.”

      “This is not a removal technology, and it’s important to state that,” Gallant stresses. “The value that it does bring is that it allows us to recycle carbon dioxide some number of times while sustaining existing industrial processes, for fewer associated emissions. Ultimately, my dream is that electrochemical systems can be used to facilitate mineralization, and permanent storage of CO2 — a true removal technology. That’s a longer-term vision. And a lot of the science we’re starting to understand is a first step toward designing those processes.”

      This research is supported by Sunway University in Malaysia. More

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      in Energy

      MIT engineers create an energy-storing supercapacitor from ancient materials

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      Two of humanity’s most ubiquitous historical materials, cement and carbon black (which resembles very fine charcoal), may form the basis for a novel, low-cost energy storage system, according to a new study. The technology could facilitate the use of renewable energy sources such as solar, wind, and tidal power by allowing energy networks to remain stable despite fluctuations in renewable energy supply.

      The two materials, the researchers found, can be combined with water to make a supercapacitor — an alternative to batteries — that could provide storage of electrical energy. As an example, the MIT researchers who developed the system say that their supercapacitor could eventually be incorporated into the concrete foundation of a house, where it could store a full day’s worth of energy while adding little (or no) to the cost of the foundation and still providing the needed structural strength. The researchers also envision a concrete roadway that could provide contactless recharging for electric cars as they travel over that road.

      The simple but innovative technology is described this week in the journal PNAS, in a paper by MIT professors Franz-Josef Ulm, Admir Masic, and Yang-Shao Horn, and four others at MIT and at the Wyss Institute for Biologically Inspired Engineering.

      Capacitors are in principle very simple devices, consisting of two electrically conductive plates immersed in an electrolyte and separated by a membrane. When a voltage is applied across the capacitor, positively charged ions from the electrolyte accumulate on the negatively charged plate, while the positively charged plate accumulates negatively charged ions. Since the membrane in between the plates blocks charged ions from migrating across, this separation of charges creates an electric field between the plates, and the capacitor becomes charged. The two plates can maintain this pair of charges for a long time and then deliver them very quickly when needed. Supercapacitors are simply capacitors that can store exceptionally large charges.

      The amount of power a capacitor can store depends on the total surface area of its conductive plates. The key to the new supercapacitors developed by this team comes from a method of producing a cement-based material with an extremely high internal surface area due to a dense, interconnected network of conductive material within its bulk volume. The researchers achieved this by introducing carbon black — which is highly conductive — into a concrete mixture along with cement powder and water, and letting it cure. The water naturally forms a branching network of openings within the structure as it reacts with cement, and the carbon migrates into these spaces to make wire-like structures within the hardened cement. These structures have a fractal-like structure, with larger branches sprouting smaller branches, and those sprouting even smaller branchlets, and so on, ending up with an extremely large surface area within the confines of a relatively small volume. The material is then soaked in a standard electrolyte material, such as potassium chloride, a kind of salt, which provides the charged particles that accumulate on the carbon structures. Two electrodes made of this material, separated by a thin space or an insulating layer, form a very powerful supercapacitor, the researchers found.

      The two plates of the capacitor function just like the two poles of a rechargeable battery of equivalent voltage: When connected to a source of electricity, as with a battery, energy gets stored in the plates, and then when connected to a load, the electrical current flows back out to provide power.

      “The material is fascinating,” Masic says, “because you have the most-used manmade material in the world, cement, that is combined with carbon black, that is a well-known historical material — the Dead Sea Scrolls were written with it. You have these at least two-millennia-old materials that when you combine them in a specific manner you come up with a conductive nanocomposite, and that’s when things get really interesting.”

      As the mixture sets and cures, he says, “The water is systematically consumed through cement hydration reactions, and this hydration fundamentally affects nanoparticles of carbon because they are hydrophobic (water repelling).” As the mixture evolves, “the carbon black is self-assembling into a connected conductive wire,” he says. The process is easily reproducible, with materials that are inexpensive and readily available anywhere in the world. And the amount of carbon needed is very small — as little as 3 percent by volume of the mix — to achieve a percolated carbon network, Masic says.

      Supercapacitors made of this material have great potential to aid in the world’s transition to renewable energy, Ulm says. The principal sources of emissions-free energy, wind, solar, and tidal power, all produce their output at variable times that often do not correspond to the peaks in electricity usage, so ways of storing that power are essential. “There is a huge need for big energy storage,” he says, and existing batteries are too expensive and mostly rely on materials such as lithium, whose supply is limited, so cheaper alternatives are badly needed. “That’s where our technology is extremely promising, because cement is ubiquitous,” Ulm says.

      The team calculated that a block of nanocarbon-black-doped concrete that is 45 cubic meters (or yards) in size — equivalent to a cube about 3.5 meters across — would have enough capacity to store about 10 kilowatt-hours of energy, which is considered the average daily electricity usage for a household. Since the concrete would retain its strength, a house with a foundation made of this material could store a day’s worth of energy produced by solar panels or windmills and allow it to be used whenever it’s needed. And, supercapacitors can be charged and discharged much more rapidly than batteries.

      After a series of tests used to determine the most effective ratios of cement, carbon black, and water, the team demonstrated the process by making small supercapacitors, about the size of some button-cell batteries, about 1 centimeter across and 1 millimeter thick, that could each be charged to 1 volt, comparable to a 1-volt battery. They then connected three of these to demonstrate their ability to light up a 3-volt light-emitting diode (LED). Having proved the principle, they now plan to build a series of larger versions, starting with ones about the size of a typical 12-volt car battery, then working up to a 45-cubic-meter version to demonstrate its ability to store a house-worth of power.

      There is a tradeoff between the storage capacity of the material and its structural strength, they found. By adding more carbon black, the resulting supercapacitor can store more energy, but the concrete is slightly weaker, and this could be useful for applications where the concrete is not playing a structural role or where the full strength-potential of concrete is not required. For applications such as a foundation, or structural elements of the base of a wind turbine, the “sweet spot” is around 10 percent carbon black in the mix, they found.

      Another potential application for carbon-cement supercapacitors is for building concrete roadways that could store energy produced by solar panels alongside the road and then deliver that energy to electric vehicles traveling along the road using the same kind of technology used for wirelessly rechargeable phones. A related type of car-recharging system is already being developed by companies in Germany and the Netherlands, but using standard batteries for storage.

      Initial uses of the technology might be for isolated homes or buildings or shelters far from grid power, which could be powered by solar panels attached to the cement supercapacitors, the researchers say.

      Ulm says that the system is very scalable, as the energy-storage capacity is a direct function of the volume of the electrodes. “You can go from 1-millimeter-thick electrodes to 1-meter-thick electrodes, and by doing so basically you can scale the energy storage capacity from lighting an LED for a few seconds, to powering a whole house,” he says.

      Depending on the properties desired for a given application, the system could be tuned by adjusting the mixture. For a vehicle-charging road, very fast charging and discharging rates would be needed, while for powering a home “you have the whole day to charge it up,” so slower-charging material could be used, Ulm says.

      “So, it’s really a multifunctional material,” he adds. Besides its ability to store energy in the form of supercapacitors, the same kind of concrete mixture can be used as a heating system, by simply applying electricity to the carbon-laced concrete.

      Ulm sees this as “a new way of looking toward the future of concrete as part of the energy transition.”

      The research team also included postdocs Nicolas Chanut and Damian Stefaniuk at MIT’s Department of Civil and Environmental Engineering, James Weaver at the Wyss Institute, and Yunguang Zhu in MIT’s Department of Mechanical Engineering. The work was supported by the MIT Concrete Sustainability Hub, with sponsorship by the Concrete Advancement Foundation. More

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      in Energy

      Shrinky Dinks, nail polish, and smelly bacteria

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      In a lab on the fourth floor of MIT’s Building 56, a group of Massachusetts high school students gathered around a device that measures conductivity.

      Vincent Nguyen, 15, from Saugus, thought of the times the material on their sample electrode flaked off the moment they took it out of the oven. Or how the electrode would fold weirdly onto itself. The big fails were kind of funny, but discouraging. The students had worked for a month, experimenting with different materials, and 17-year-old Brianna Tong of Malden wondered if they’d finally gotten it right: Would their electrode work well enough to power a microbial fuel cell?

      The students secured their electrode with alligator clips, someone hit start, and the teens watched anxiously as the device searched for even the faintest electrical current.

      Capturing electrons from bacteria

      Last July, Tong, Nguyen, and six other students from Malden Catholic High School commuted between the lab of MIT chemical engineer Ariel L. Furst and their school’s chemistry lab. Their goal was to fashion electrodes for low-cost microbial fuel cells — miniature bioreactors that generate small amounts of electricity by capturing electrons transferred from living microbes. These devices can double as electrochemical sensors.

      Furst, the Paul M. Cook Career Development Professor of Chemical Engineering, uses a mix of electrochemistry, microbial engineering, and materials science to address challenges in human health and clean energy. “The goal of all of our projects is to increase sustainability, clean energy, and health equity globally,” she says.

      Electrochemical sensors are powerful, sensitive detection and measurement tools. Typically, their electrodes need to be built in precisely engineered environments. “Thinking about ways of making devices without needing a cleanroom is important for coming up with inexpensive devices that can be deployed in low-resource settings under non-ideal conditions,” Furst says.

      For 17-year-old Angelina Ang of Everett, the project illuminated the significance of “coming together to problem-solve for a healthier and more sustainable earth,” she says. “It made me realize that we hold the answers to fix our dying planet.”

      With the help of a children’s toy called Shrinky Dinks, carbon-based materials, nail polish, and a certain smelly bacterium, the students got — literally — a trial-by-fire introduction to the scientific method. At one point, one of their experimental electrodes burst into flames. Other results were more promising.

      The students took advantage of the electrical properties of a bacterium — Shewanella oneidensis — that’s been called nature’s microscopic power plant. As part of their metabolism, Shewanella oneidensis generate electricity by oxidizing organic matter. In essence, they spit out electrons. Put enough together, and you get a few milliamps.

      To build bacteria-friendly electrodes, one of the first things the students did was culture Shewanella. They learned how to pour a growth medium into petri dishes where the reddish, normally lake-living bacteria could multiply. The microbes, Furst notes, are a little stinky, like cabbage. “But we think they’re really cool,” she says.

      With the right engineering, Shewanella can produce electric current when they detect toxins in water or soil. They could be used for bioremediation of wastewater. Low-cost versions could be useful for areas with limited or no access to reliable electricity and clean water.

      Next-generation chemists

      The Malden Catholic-MIT program resulted from a fluke encounter between Furst and a Malden Catholic parent.

      Mary-Margaret O’Donnell-Zablocki, then a medicinal chemist at a Kendall Square biotech startup, met Furst through a mutual friend. She asked Furst if she’d consider hosting high school chemistry students in her lab for the summer.

      Furst was intrigued. She traces her own passion for science to a program she’d happened upon between her junior and senior years in high school in St. Louis. The daughter of a software engineer and a businesswoman, Furst was casting around for potential career interests when she came across a summer program that enlisted scientists in academia and private research to introduce high school students and teachers to aspects of the scientific enterprise.

      “That’s when I realized that research is not like a lab class where there’s an expected outcome,” Furst recalls. “It’s so much cooler than that.”

      Using startup funding from an MIT Energy Initiative seed grant, Furst developed a curriculum with Malden Catholic chemistry teacher Seamus McGuire, and students were invited to apply. In addition to Tong, Ang, and Nguyen, participants included Chengxiang Lou, 18, from China; Christian Ogata, 14, of Wakefield; Kenneth Ramirez, 17, of Everett; Isaac Toscano, 17, of Medford; and MaryKatherine Zablocki, 15, of Revere and Wakefield. O’Donnell-Zablocki was surprised — and pleased — when her daughter applied to the program and was accepted.

      Furst notes that women are still underrepresented in chemical engineering. She was particularly excited to mentor young women through the program.

      A conductive ink

      The students were charged with identifying materials that had high conductivity, low resistance, were a bit soluble, and — with the help of a compatible “glue” — were able to stick to a substrate.

      Furst showed the Malden Catholic crew Shrinky Dinks — a common polymer popularized in the 1970s as a craft material that, when heated in a toaster oven, shrinks to a third of its size and becomes thicker and more rigid. Electrodes based on Shrinky Dinks would cost pennies, making it an ideal, inexpensive material for microbial fuel cells that could monitor, for instance, soil health in low- and middle-income countries.

      “Right now, monitoring soil health is problematic,” Furst says. “You have to collect a sample and bring it back to the lab to analyze in expensive equipment. But if we have these little devices that cost a couple of bucks each, we can monitor soil health remotely.”

      After a crash course in conductive carbon-based inks and solvent glues, the students went off to Malden Catholic to figure out what materials they wanted to try.

      Tong rattled them off: carbon nanotubes, carbon nanofibers, graphite powder, activated carbon. Potential solvents to help glue the carbon to the Shrinky Dinks included nail polish, corn syrup, and embossing ink, to name a few. They tested and retested. When they hit a dead end, they revised their hypotheses.

      They tried using a 3D printed stencil to daub the ink-glue mixture onto the Shrinky Dinks. They hand-painted them. They tried printing stickers. They worked with little squeegees. They tried scooping and dragging the material. Some of their electro-materials either flaked off or wouldn’t stick in the heating process.

      “Embossing ink never dried after baking the Shrinky Dink,” Ogata recalls. “In fact, it’s probably still liquid! And corn syrup had a tendency to boil. Seeing activated carbon ignite or corn syrup boiling in the convection oven was quite the spectacle.”

      “After the electrode was out of the oven and cooled down, we would check the conductivity,” says Tong, who plans to pursue a career in science. “If we saw there was a high conductivity, we got excited and thought those materials worked.”

      The moment of truth came in Furst’s MIT lab, where the students had access to more sophisticated testing equipment. Would their electrodes conduct electricity?

      Many of them didn’t. Tong says, “At first, we were sad, but then Dr. Furst told us that this is what science is, testing repeatedly and sometimes not getting the results we wanted.” Lou agrees. “If we just copy the data left by other scholars and don’t collect and figure it out by ourselves, then it is difficult to be a qualified researcher,” he says.

      Some of the students plan to continue the project one afternoon a week at MIT and as an independent study at Malden Catholic. The long-term goal is to create a field-based soil sensor that employs a bacterium like Shewanella.

      By chance, the students’ very first electrode — made of graphite powder ink and nail polish glue — generated the most current. One of the team’s biggest surprises was how much better black nail polish worked than clear nail polish. It turns out black nail polish contains iron-based pigment — a conductor. The unexpected win took some of the sting out of the failures.

      “They learned a very hard lesson: Your results might be awesome, and things are exciting, but then nothing else might work. And that’s totally fine,” Furst says.

      This article appears in the Winter 2023 issue of Energy Futures, the magazine of the MIT Energy Initiative. More

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      in Environment

      Nanotube sensors are capable of detecting and distinguishing gibberellin plant hormones

      by

      Researchers from the Disruptive and Sustainable Technologies for Agricultural Precision (DiSTAP) interdisciplinary research group of the Singapore-MIT Alliance for Research and Technology (SMART), MIT’s research enterprise in Singapore, and their collaborators from Temasek Life Sciences Laboratory have developed the first-ever nanosensor that can detect and distinguish gibberellins (GAs), a class of hormones in plants that are important for growth. The novel nanosensors are nondestructive, unlike conventional collection methods, and have been successfully tested in living plants. Applied in the field for early-stage plant stress monitoring, the sensors could prove transformative for agriculture and plant biotechnology, giving farmers interested in high-tech precision agriculture and crop management a valuable tool to optimize yield.

      The researchers designed near-infrared fluorescent carbon nanotube sensors that are capable of detecting and distinguishing two plant hormones, GA3 and GA4. Belonging to a class of plant hormones known as gibberellins, GA3 and GA4 are diterpenoid phytohormones produced by plants that play an important role in modulating diverse processes involved in plant growth and development. GAs are thought to have played a role in the driving forces behind the “green revolution” of the 1960s, which was in turn credited with averting famine and saving the lives of many worldwide. The continued study of gibberellins could lead to further breakthroughs in agricultural science and have implications for food security.

      Climate change, global warming, and rising sea levels cause farming soil to get contaminated by saltwater, raising soil salinity. In turn, high soil salinity is known to negatively regulate GA biosynthesis and promote GA metabolism, resulting in the reduction of GA content in plants. The new nanosensors developed by the SMART researchers allow for the study of GA dynamics in living plants under salinity stress at a very early stage, potentially enabling farmers to make early interventions when eventually applied in the field. This forms the basis of early-stage stress detection.

      Currently, methods to detect GA3 and GA4 typically require mass spectroscopy-based analysis, a time-consuming and destructive process. In contrast, the new sensors developed by the researchers are highly selective for the respective GAs and offer real-time, in vivo monitoring of changes in GA levels across a broad range of plant species.

      Described in a paper titled “Near-Infrared Fluorescent Carbon Nanotube Sensors for the Plant Hormone Family Gibberellins” published in the journal Nano Letters, the research represents a breakthrough for early-stage plant stress detection and holds tremendous potential to advance plant biotechnology and agriculture. This paper builds on previous research by the team at SMART DiSTAP on single-walled carbon nanotube-based nanosensors using the corona phase molecular recognition (CoPhMoRe) platform.

      Based on the CoPhMoRe concept introduced by the lab of MIT Professor Professor Michael Strano, the novel sensors are able to detect GA kinetics in the roots of a variety of model and non-model plant species, including Arabidopsis, lettuce, and basil, as well as GA accumulation during lateral root emergence, highlighting the importance of GA in root system architecture. This was made possible by the researchers’ related development of a new coupled Raman/near infrared fluorimeter that enables self-referencing of nanosensor near infrared fluorescence with its Raman G-band, a new hardware innovation that removes the need for a separate reference nanosensor and greatly simplifies the instrumentation requirements by using a single optical channel to measure hormone concentration.

      Using the reversible GA nanosensors, the researchers detected increased endogenous GA levels in mutant plants producing greater amounts of GA20ox1, a key enzyme in GA biosynthesis, as well as decreased GA levels in plants under salinity stress. When exposed to salinity stress, researchers also found that lettuce growth was severely stunted — an indication that only became apparent after 10 days. In contrast, the GA nanosensors reported decreased GA levels after just six hours, demonstrating their efficacy as a much earlier indicator of salinity stress.

      “Our CoPhMoRe technique allows us to create nanoparticles that act like natural antibodies in that they can recognize and lock onto specific molecules. But they tend to be far more stable than alternatives. We have used this method to successfully create nanosensors for plant signals such as hydrogen peroxide and heavy-metal pollutants like arsenic in plants and soil,” says Strano, the Carbon P. Dubbs Professor of Chemical Engineering at MIT who is co-corresponding author and DiSTAP co-lead principal investigator. “The method works to create sensors for organic molecules like synthetic auxin — an important plant hormone — as we have shown. This latest breakthrough now extends this success to a plant hormone family called gibberellins — an exceedingly difficult one to recognize.”

      Strano adds: “The resulting technology offers a rapid, real-time, and in vivo method to monitor changes in GA levels in virtually any plant, and can replace current sensing methods which are laborious, destructive, species-specific, and much less efficient.”

      Mervin Chun-Yi Ang, associate scientific director at DiSTAP and co-first author of the paper, says, “More than simply a breakthrough in plant stress detection, we have also demonstrated a hardware innovation in the form of a new coupled Raman/NIR fluorimeter that enabled self-referencing of SWNT sensor fluorescence with its Raman G-band, representing a major advance in the translation of our nanosensing tool sets to the field. In the near future, our sensors can be combined with low-cost electronics, portable optodes, or microneedle interfaces for industrial use, transforming how the industry screens for and mitigates plant stress in food crops and potentially improving growth and yield.”

      The new sensors could yet have a variety of industrial applications and use cases. Daisuke Urano, a Temasek Life Sciences Laboratory principal investigator, National University of Singapore (NUS) adjunct assistant professor, and co-corresponding author of the paper, explains, “GAs are known to regulate a wide range of plant development processes, from shoot, root, and flower development, to seed germination and plant stress responses. With the commercialization of GAs, these plant hormones are also sold to growers and farmers as plant growth regulators to promote plant growth and seed germination. Our novel GA nanosensors could be applied in the field for early-stage plant stress monitoring, and also be used by growers and farmers to track the uptake or metabolism of GA in their crops.”

      The design and development of the nanosensors, creation and validation of the coupled Raman/near infrared fluorimeter and related image/data processing algorithms, as well as statistical analysis of readouts from plant sensors for this study were performed by SMART and MIT. The Temasek Life Sciences Laboratory was responsible for the design, execution, and analysis of plant-related studies, including validation of nanosensors in living plants.

      This research was carried out by SMART and supported by the National Research Foundation of Singapore under its Campus for Research Excellence And Technological Enterprise (CREATE) program. The DiSTAP program, led by Strano and Singapore co-lead principal investigator Professor Chua Nam Hai, addresses deep problems in food production in Singapore and the world by developing a suite of impactful and novel analytical, genetic, and biomaterial technologies. The goal is to fundamentally change how plant biosynthetic pathways are discovered, monitored, engineered, and ultimately translated to meet the global demand for food and nutrients. Scientists from MIT, Temasek Life Sciences Laboratory, Nanyang Technological University (NTU) and NUS are collaboratively developing new tools for the continuous measurement of important plant metabolites and hormones for novel discovery, deeper understanding and control of plant biosynthetic pathways in ways not yet possible, especially in the context of green leafy vegetables; leveraging these new techniques to engineer plants with highly desirable properties for global food security, including high yield density production, and drought and pathogen resistance, and applying these technologies to improve urban farming.

      SMART was established by MIT and the National Research Foundation of Singapore in 2007. SMART serves as an intellectual and innovation hub for research interactions between MIT and Singapore, undertaking cutting-edge research projects in areas of interest to both Singapore and MIT. SMART currently comprises an Innovation Center and five interdisciplinary research groups: Antimicrobial Resistance, Critical Analytics for Manufacturing Personalized-Medicine, DiSTAP, Future Urban Mobility, and Low Energy Electronic Systems. More