Most systems used to detect toxic gases in industrial or domestic settings can be used only once, or at best a few times. Now, researchers at MIT have developed a detector that could provide continuous monitoring for the presence of these gases, at low cost.
The new system combines two existing technologies, bringing them together in a way that preserves the advantages of each while avoiding their limitations. The team used a material called a metal-organic framework, or MOF, which is highly sensitive to tiny traces of gas but whose performance quickly degrades, and combined it with a polymer material that is highly durable and easier to process, but much less sensitive.
The <a href="https://onlinelibrary.wiley.com/doi/10.1002/adma.202312382">results are reported today</a> in the journal Advanced Materials, in a paper by MIT professors Aristide Gumyusenge, <a href="https://chemistry.mit.edu/profile/mircea-dinca/">Mircea Dinca</a>, <a href="https://chemistry.mit.edu/profile/heather-j-kulik/">Heather Kulik</a>, and Jesus del Alamo, graduate student Heejung Roh, and postdocs Dong-Ha Kim, Yeongsu Cho, and Young-Moo Jo.
<img src="https://storage.googleapis.com/labrulez-bucket-strapi-h3hsga3/MIT_MIT_News_courtesy_of_the_researchers_Researchers_develop_a_detector_for_continuously_monitoring_toxic_gases_To_create_their_detector_the_team_used_a_material_called_a_metal_organic_4957059d20.jpg" alt="MIT - MIT News; courtesy of the researchers: To create their detector, the team used a material called a metal-organic framework, or MOF (pictured as the black lattice), which is highly sensitive to tiny traces of gas but whose performance quickly degrades. They combined the MOF with a polymer material, shown as the teal translucent strands, that is highly durable but much less sensitive."/>
Highly porous and with large surface areas, MOFs come in a variety of compositions. Some can be insulators, but the ones used for this work are highly electrically conductive. With their sponge-like form, they are effective at capturing molecules of various gases, and the sizes of their pores can be tailored to make them selective for particular kinds of gases. “If you are using them as a sensor, you can recognize if the gas is there if it has an effect on the resistivity of the MOF,” says Gumyusenge, the paper’s senior author and the Merton C. Flemings Career Development Assistant Professor of Materials Science and Engineering.
The drawback for these materials’ use as detectors for gases is that they readily become saturated, and then can no longer detect and quantify new inputs. “That’s not what you want. You want to be able to detect and reuse,” Gumyusenge says. “So, we decided to use a polymer composite to achieve this reversibility.”
The team used a class of conductive polymers that Gumyusenge and his co-workers had <a href="https://pubs.acs.org/doi/10.1021/acssensors.3c01530">previously shown</a> can respond to gases without permanently binding to them. “The polymer, even though it doesn’t have the high surface area that the MOFs do, will at least provide this recognize-and-release type of phenomenon,” he says.
The team combined the polymers in a liquid solution along with the MOF material in powdered form, and deposited the mixture on a substrate, where they dry into a uniform, thin coating. By combining the polymer, with its quick detection capability, and the more sensitive MOFs, in a one-to-one ratio, he says, “suddenly we get a sensor that has both the high sensitivity we get from the MOF and the reversibility that is enabled by the presence of the polymer.”
The material changes its electrical resistance when molecules of the gas are temporarily trapped in the material. These changes in resistance can be continuously monitored by simply attaching an ohmmeter to track the resistance over time. Gumyusenge and his students demonstrated the composite material’s ability to detect nitrogen dioxide, a toxic gas produced by many kinds of combustion, in a small lab-scale device. After 100 cycles of detection, the material was still maintaining its baseline performance within a margin of about 5 to 10 percent, demonstrating its long-term use potential.
In addition, this material has far greater sensitivity than most presently used detectors for nitrogen dioxide, the team reports. This gas is often detected after the use of <a href="https://www.science.org/doi/10.1126/sciadv.adm8680">stove ovens</a>. And, with this gas recently linked to many asthma cases in the U.S., reliable detection in low concentrations is important. The team demonstrated that this new composite could detect, reversibly, the gas at concentrations as low as 2 parts per million.
While their demonstration was specifically aimed at nitrogen dioxide, Gumyusenge says, “we can definitely tailor the chemistry to target other volatile molecules,” as long as they are small polar analytes, “which tend to be most of the toxic gases.”
Besides being compatible with a simple hand-held detector or a smoke-alarm type of device, one advantage of the material is that the polymer allows it to be deposited as an extremely thin uniform film, unlike regular MOFs, which are generally in an inefficient powder form. Because the films are so thin, there is little material needed and production material costs could be low; the processing methods could be typical of those used for industrial coating processes. “So, maybe the limiting factor will be scaling up the synthesis of the polymers, which we’ve been synthesizing in small amounts,” Gumyusenge says.
“The next steps will be to evaluate these in real-life settings,” he says. For example, the material could be applied as a coating on chimneys or exhaust pipes to continuously monitor gases through readings from an attached resistance monitoring device. In such settings, he says, “we need tests to check if we truly differentiate it from other potential contaminants that we might have overlooked in the lab setting. Let’s put the sensors out in real-world scenarios and see how they do.”
The work was supported by the MIT Climate and Sustainability Consortium (MCSC), the Abdul Latif Jameel Water and Food Systems Lab (J-WAFS) at MIT, and the U.S. Department of Energy.

Researchers develop a detector for continuously monitoring toxic gases

New research from the group of MIT Professor <a href="https://chemistry.mit.edu/profile/brett-mcguire/">Brett McGuire</a> has revealed the presence of a previously unknown molecule in space. The team’s open-access paper, “<a href="https://iopscience.iop.org/article/10.3847/2041-8213/ad37ff">Rotational Spectrum and First Interstellar Detection of 2-Methoxyethanol Using ALMA Observations of NGC 6334I</a>,” appears in April 12 issue of The Astrophysical Journal Letters.
<a href="https://chemistry.mit.edu/chemistry-news/zachary-fried-wins-lewis-e-snyder-astrochemistry-award/">Zachary T.P. Fried</a>, a <a href="https://chemistry.mit.edu/chemistry-news/graduate-student-spotlight-zachary-fried/">graduate student in the McGuire group</a> and the lead author of the publication, worked to assemble a puzzle comprised of pieces collected from across the globe, extending beyond MIT to France, Florida, Virginia, and Copenhagen, to achieve this exciting discovery.
“Our group tries to understand what molecules are present in regions of space where stars and solar systems will eventually take shape,” explains Fried. “This allows us to piece together how chemistry evolves alongside the process of star and planet formation. We do this by looking at the rotational spectra of molecules, the unique patterns of light they give off as they tumble end-over-end in space. These patterns are fingerprints (barcodes) for molecules. To detect new molecules in space, we first must have an idea of what molecule we want to look for, then we can record its spectrum in the lab here on Earth, and then finally we look for that spectrum in space using telescopes.”
<img src="https://storage.googleapis.com/labrulez-bucket-strapi-h3hsga3/MIT_MIT_News_courtesy_of_the_researchers_Researchers_detect_a_new_molecule_in_space_Scientists_detected_2_Methoxyethanol_in_space_for_the_first_time_using_radiotelescope_observations_3e67581c6d.jpg" alt="MIT News/courtesy of the researchers: Scientists detected 2-Methoxyethanol in space for the first time using radiotelescope observations of the star-forming region NGC 6334I."/>
<h4>Searching for molecules in space</h4>
The McGuire Group has recently <a href="https://iopscience.iop.org/article/10.3847/2041-8213/abe764/meta">begun to utilize machine learning</a> to suggest good target molecules to search for. In 2023, one of these machine learning models suggested the researchers target a molecule known as 2-methoxyethanol.
“There are a number of ‘methoxy’ molecules in space, like dimethyl ether, methoxymethanol, ethyl methyl ether, and methyl formate, but 2-methoxyethanol would be the largest and most complex ever seen,” says Fried. To detect this molecule using radiotelescope observations, the group first needed to measure and analyze its rotational spectrum on Earth. The researchers combined experiments from the University of Lille (Lille, France), the New College of Florida (Sarasota, Florida), and the McGuire lab at MIT to measure this spectrum over a broadband region of frequencies ranging from the microwave to sub-millimeter wave regimes (approximately 8 to 500 gigahertz).
The data gleaned from these measurements permitted a search for the molecule using Atacama Large Millimeter/submillimeter Array (ALMA) observations toward two separate star-forming regions: NGC 6334I and IRAS 16293-2422B. Members of the McGuire group analyzed these telescope observations alongside researchers at the National Radio Astronomy Observatory (Charlottesville, Virginia) and the University of Copenhagen, Denmark.
“Ultimately, we observed 25 rotational lines of 2-methoxyethanol that lined up with the molecular signal observed toward NGC 6334I (the barcode matched!), thus resulting in a secure detection of 2-methoxyethanol in this source,” says Fried. “This allowed us to then derive physical parameters of the molecule toward NGC 6334I, such as its abundance and excitation temperature. It also enabled an investigation of the possible chemical formation pathways from known interstellar precursors.”
<h4>Looking forward</h4>
Molecular discoveries like this one help the researchers to better understand the development of molecular complexity in space during the star formation process. 2-methoxyethanol, which contains 13 atoms, is quite large for interstellar standards — as of 2021, <a href="https://iopscience.iop.org/article/10.3847/1538-4365/ac2a48/meta">only six species larger than 13 atoms were detected outside the solar system</a>, many by McGuire’s group, and all of them existing as ringed structures.
“Continued observations of large molecules and subsequent derivations of their abundances allows us to advance our knowledge of how efficiently large molecules can form and by which specific reactions they may be produced,” says Fried. “Additionally, since we detected this molecule in NGC 6334I but not in IRAS 16293-2422B, we were presented with a unique opportunity to look into how the differing physical conditions of these two sources may be affecting the chemistry that can occur.”

Researchers detect a new molecule in space

<div>Perovskites, a broad class of compounds with a particular kind of crystal structure, have long been seen as a promising alternative or supplement to today’s silicon or cadmium telluride solar panels. They could be far more lightweight and inexpensive, and could be coated onto virtually any substrate, including paper or flexible plastic that could be rolled up for easy transport.In their efficiency at converting sunlight to electricity, perovskites are becoming comparable to silicon, whose manufacture still requires long, complex, and energy-intensive processes. One big remaining drawback is longevity: They tend to break down in a matter of months to years, while silicon solar panels can last more than two decades. And their efficiency over large module areas still lags behind silicon. Now, a team of researchers at MIT and several other institutions has revealed ways to optimize efficiency and better control degradation, by engineering the nanoscale structure of perovskite devices.The study reveals new insights on how to make high-efficiency perovskite solar cells, and also provides new directions for engineers working to bring these solar cells to the commercial marketplace. The work is <a target="_blank" rel="noopener noreferrer" href="https://www.nature.com/articles/s41560-024-01470-5">described today in the journal Nature Energy</a>, in a paper by Dane deQuilettes, a recent MIT postdoc who is now co-founder and chief science officer of the MIT spinout Optigon, along with MIT professors Vladimir Bulovic and <a target="_blank" rel="noopener noreferrer" href="https://chemistry.mit.edu/profile/moungi-bawendi/">Moungi Bawendi</a>, and 10 others at MIT and in Washington state, the U.K., and Korea.“Ten years ago, if you had asked us what would be the ultimate solution to the rapid development of solar technologies, the answer would have been something that works as well as silicon but whose manufacturing is much simpler,” Bulovic says. “And before we knew it, the field of perovskite photovoltaics appeared. They were as efficient as silicon, and they were as easy to paint on as it is to paint on a piece of paper. The result was tremendous excitement in the field.”Nonetheless, “there are some significant technical challenges of handling and managing this material in ways we’ve never done before,” he says. But the promise is so great that many hundreds of researchers around the world have been working on this technology. The new study looks at a very small but key detail: how to “passivate” the material’s surface, changing its properties in such a way that the perovskite no longer degrades so rapidly or loses efficiency.<img src="https://storage.googleapis.com/labrulez-bucket-strapi-h3hsga3/MIT_Courtesy_of_the_researchers_Study_unlocks_nanoscale_secrets_for_designing_next_generation_solar_cells_A_team_of_MIT_researchers_and_several_other_institutions_has_revealed_ways_to_226e99db52.jpg" alt="MIT / Courtesy of the researchers: Study unlocks nanoscale secrets for designing next-generation solar cells - A team of MIT researchers and several other institutions has revealed ways to." srcset="https://storage.googleapis.com/labrulez-bucket-strapi-h3hsga3/thumbnail_MIT_Courtesy_of_the_researchers_Study_unlocks_nanoscale_secrets_for_designing_next_generation_solar_cells_A_team_of_MIT_researchers_and_several_other_institutions_has_revealed_ways_to_226e99db52.jpg 234w," sizes="100vw" width="1536" height="1024">“The key is identifying the chemistry of the interfaces, the place where the perovskite meets other materials,” Bulovic says, referring to the places where different materials are stacked next to perovskite in order to facilitate the flow of current through the device.Engineers have developed methods for passivation, for example by using a solution that creates a thin passivating coating. But they’ve lacked a detailed understanding of how this process works — which is essential to make further progress in finding better coatings. The new study “addressed the ability to passivate those interfaces and elucidate the physics and science behind why this passivation works as well as it does,” Bulovic says.The team used some of the most powerful instruments available at laboratories around the world to observe the interfaces between the perovskite layer and other materials, and how they develop, in unprecedented detail. This close examination of the passivation coating process and its effects resulted in “the clearest roadmap as of yet of what we can do to fine-tune the energy alignment at the interfaces of perovskites and neighboring materials,” and thus improve their overall performance, Bulovic says.While the bulk of a perovskite material is in the form of a perfectly ordered crystalline lattice of atoms, this order breaks down at the surface. There may be extra atoms sticking out or vacancies where atoms are missing, and these defects cause losses in the material’s efficiency. That’s where the need for passivation comes in.“This paper is essentially revealing a guidebook for how to tune surfaces, where a lot of these defects are, to make sure that energy is not lost at surfaces,” deQuilettes says. “It’s a really big discovery for the field,” he says. “This is the first paper that demonstrates how to systematically control and engineer surface fields in perovskites.”The common passivation method is to bathe the surface in a solution of a salt called hexylammonium bromide, a technique developed at MIT several years ago by Jason Jungwan Yoo PhD ’20, who is a co-author of this paper, that led to multiple new world-record efficiencies. By doing that “you form a very thin layer on top of your defective surface, and that thin layer actually passivates a lot of the defects really well,” deQuilettes says. “And then the bromine, which is part of the salt, actually penetrates into the three-dimensional layer in a controllable way.” That penetration helps to prevent electrons from losing energy to defects at the surface.These two effects, produced by a single processing step, produces the two beneficial changes simultaneously. “It’s really beautiful because usually you need to do that in two steps,” deQuilettes says.The passivation reduces the energy loss of electrons at the surface after they have been knocked loose by sunlight. These losses reduce the overall efficiency of the conversion of sunlight to electricity, so reducing the losses boosts the net efficiency of the cells.That could rapidly lead to improvements in the materials’ efficiency in converting sunlight to electricity, he says. The recent efficiency records for a single perovskite layer, several of them set at MIT, have ranged from about 24 to 26 percent, while the maximum theoretical efficiency that could be reached is about 30 percent, according to deQuilettes.An increase of a few percent may not sound like much, but in the solar photovoltaic industry such improvements are highly sought after. “In the silicon photovoltaic industry, if you’re gaining half of a percent in efficiency, that’s worth hundreds of millions of dollars on the global market,” he says. A recent shift in silicon cell design, essentially adding a thin passivating layer and changing the doping profile, provides an efficiency gain of about half of a percent. As a result, “the whole industry is shifting and rapidly trying to push to get there.” The overall efficiency of silicon solar cells has only seen very small incremental improvements for the last 30 years, he says.The record efficiencies for perovskites have mostly been set in controlled laboratory settings with small postage-stamp-size samples of the material. “Translating a record efficiency to commercial scale takes a long time,” deQuilettes says. “Another big hope is that with this understanding, people will be able to better engineer large areas to have these passivating effects.”There are hundreds of different kinds of passivating salts and many different kinds of perovskites, so the basic understanding of the passivation process provided by this new work could help guide researchers to find even better combinations of materials, the researchers suggest. “There are so many different ways you could engineer the materials,” he says.“I think we are on the doorstep of the first practical demonstrations of perovskites in the commercial applications,” Bulovic says. “And those first applications will be a far cry from what we’ll be able to do a few years from now.” He adds that perovskites “should not be seen as a displacement of silicon photovoltaics. It should be seen as an augmentation — yet another way to bring about more rapid deployment of solar electricity.”“A lot of progress has been made in the last two years on finding surface treatments that improve perovskite solar cells,” says Michael McGehee, a professor of chemical engineering at the University of Colorado who was not associated with this research. “A lot of the research has been empirical with the mechanisms behind the improvements not being fully understood. This detailed study shows that treatments can not only passivate defects, but can also create a surface field that repels carriers that should be collected at the other side of the device. This understanding might help further improve the interfaces.”The team included researchers at the Korea Research Institute of Chemical Technology, Cambridge University, the University of Washington in Seattle, and Sungkyunkwan University in Korea. The work was supported by the Tata Trust, the MIT Institute for Soldier Nanotechnologies, the U.S. Department of Energy, and the U.S. National Science Foundation.</div>

Study unlocks nanoscale secrets for designing next-generation solar cells

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