Rwandan scientist leads MIT team in creating high-tech detectors for toxic gases

Researchers from the Massachusetts Institute of Technology (MIT), led by Rwandan professor Aristide Gumyusenge, have developed a detector that can provide continuous monitoring for the presence of toxic gases at home or in industrial environments at a low cost.

The new system combines two existing technologies and brings them together in a way that preserves the benefits of each and avoids their limitations.

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The team used a material called a metal-organic framework (MOF), which is very sensitive to small traces of gas but whose performance degrades quickly, and combined it with a polymer material that is very durable and easier to process, but much less sensitive. .

MOFs are highly porous, have a large surface area and are available in various compositions. Some may be insulators, but the ones used for this work are highly electrically conductive.

With their spongy shape, they are effective at trapping molecules of different gases, and the sizes of their pores can be adjusted to make them selective for certain types of gases.

Rwandan professor Aristide Gumyusenge, team leader of researchers who developed that new system. Politeness

“Using them as a sensor, you can recognize whether the gas is present if it has an effect on the resistance of the MOF,” said Gumyusenge, senior author of the paper.

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During the development of the sensors, the team faced a number of challenges, including the fact that MOF materials easily become saturated with gases and subsequently become unable to detect and quantify new inputs.

“That’s not what you want. You want to be able to detect and reuse. That’s why we decided to use a polymer composite to achieve this reversibility,” he noted.

The team used a class of conducting polymers that Gumyusenge and his colleagues had previously shown can react with gases without permanently bonding to them.

“The polymer, even if it doesn’t have the large surface area that the MOFs have, will at least provide this ‘recognition and release’ phenomenon,” he added.

They combined the polymers in a liquid solution along with the powdered MOF material and applied the mixture to a substrate, where it dried to form a uniform, thin coating.

By combining the polymer, with its fast sensing ability, and the more sensitive MOFs in a one-to-one ratio, he said, “Suddenly we get a sensor that has both the high sensitivity we get from the MOF and the reversibility that is made possible by the presence of the polymer.”

The material changes its electrical resistance when molecules of the gas are temporarily trapped in the material. These resistance changes can be monitored continuously by simply connecting an ohmmeter to monitor resistance over time.

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Gumyusenge and his students demonstrated the composite material’s ability to detect nitrogen dioxide, a toxic gas produced by many types of combustion, in a small laboratory-scale device. After 100 detection cycles, the material still retained its baseline performance within a range of approximately 5 to 10 percent, demonstrating its long-term use potential.

In addition, the material has much greater sensitivity than most currently used detectors for nitrogen dioxide, the team reports. This gas is often detected after the use of stoves.

And because this gas has recently been linked to many asthma cases in the US, reliable detection at low concentrations is important. The team showed that this new composite could reversibly detect the gas at concentrations as low as two parts per million.

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Although their demonstration focused specifically on nitrogen dioxide, Gumyusenge said, “We can certainly tune the chemistry to other volatile molecules,” as long as they are small polar analytes, “which tend to make up most of the toxic gases.”

In addition to being compatible with a simple handheld detector or a smoke detector type device, an 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 be inefficient. powder form.

Because the films are so thin, little material is required and production material costs can be low; the processing methods could be typical of those used for industrial coating processes.

“So perhaps the limiting factor will be scaling up the synthesis of the polymers, which we synthesized in small quantities,” Gumyusenge said. “The next steps will be to evaluate these in practice,” he added.

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