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Thin Coating Detects, Monitors Toxic Gases

THURSDAY, MAY 30, 2024

A new material produced by a team from the Massachusetts Institute of Technology could be used as a thin coating to analyze air quality in industrial or home settings.

The results were recently published in the journal Advanced Materials. Authors include MIT professors Aristide Gumyusenge, Mircea Dinca, Heather Kulik and Jesus del Alamo; graduate student Heejung Roh; and postdocs Dong-Ha Kim, Yeongsu Cho and Young-Moo Jo.

About the Material

According to MIT, the new system combines a metal-organic framework, or MOF, which is sensitive to traces of gas but whose performance quickly degrades, and a polymer material that is durable and easier to process, but much less sensitive.

While some MOFs can act as insulators, the researchers used a highly electrically conductive MOF for their work. These are reportedly effective at capturing gas molecules with their sponge-like form, and the pore sizes can be tailored to be selective for particular kinds of gas.

“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,” said Gumyusenge, the paper’s senior author and the Merton C. Flemings Career Development Assistant Professor of Materials Science and Engineering.

However, the team notes that 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 said. “So, we decided to use a polymer composite to achieve this reversibility.”

The researchers used a class of conductive polymers that Gumyusenge and his co-workers had previously found 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 explained.

The polymers were combined in a liquid solution with the MOF material in powder form before depositing the mixture on the substrate. Afterwards, it dried into a uniform, thin coating.

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By combining the polymer and the more sensitive MOFs in a one-to-one ratio, Gumyusenge said, “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 reportedly changes its electrical resistance when molecules of the gas are temporarily trapped in the material. These changes in resistance can be continuously monitored by attaching an ohmmeter to track the resistance over time.

The team then 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 reportedly was still maintaining its baseline performance within a margin of about 5-10%.

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Additionally, the material was found to have “far greater sensitivity” than most presently used detectors for nitrogen dioxide. The team reports that this new composite could detect, reversibly, the gas at concentrations as low as 2 parts per million.

While testing was aimed at nitrogen dioxide, Gumyusenge said that the team “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.”

Another advantage of the material, the researchers add, is that the polymer allows it to be deposited as an extremely thin uniform film unlike regular MOFs. Because of its thin property, little material is needed to keep production material costs low and processing methods could be typical of those used for industrial coating processes.

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“So, maybe the limiting factor will be scaling up the synthesis of the polymers, which we’ve been synthesizing in small amounts,” Gumyusenge noted.

The next steps in the research will be to evaluate the material in real-life setting, Gumyusenge said. 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.

“We need tests to check if we truly differentiate it from other potential contaminants that we might have overlooked in the lab setting,” he continued. “Let’s put the sensors out in real-world scenarios and see how they do.”

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The work was supported by the MIT Climate and Sustainability Consortium, the Abdul Latif Jameel Water and Food Systems Lab at MIT and the U.S. Department of Energy.


Tagged categories: Air quality; Coating chemistry; Coating Materials; Coatings; Colleges and Universities; Emissions; Gas detectors; Health & Safety; Health and safety; Polymers; Research and development


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