Detecting nitrogen dioxide

Australian and Chinese researchers have developed a low-cost and reliable method of detecting nitrogen dioxide (NO₂) — an air pollutant that contributes to more than seven million deaths worldwide each year.

Nitrogen dioxide increases the risk of respiratory disorders in children and can severely affect the elderly. The main contributors of the gas are the burning of fossil fuels — particularly in coal-fired power stations and diesel engines, which can impact on the health of people in urban areas. Furthermore, there are still significant challenges for NO₂ sensing at low detection limits — especially in the presence of other interfering gases.

“A lack of public access to effective monitoring tools is a major roadblock to mitigating the harmful effects of this gas — but current sensing systems are either very expensive or have serious difficulty distinguishing it from other gases,” said Professor Kourosh Kalantar-zadeh, from RMIT University’s Centre for Advanced Electronics and Sensors.

Professor Kalantar-zadeh said the negative impact of NO₂ could be prevented by access to personalised, selective, sensitive and reliable monitoring systems that could detect harmful levels of the gas early. With the help of fellow RMIT researchers and colleagues from the Chinese Academy of Sciences, that is exactly what he has created.

“The method we have developed is not only more cost effective, it also works better than the sensors currently used to detect this dangerous gas.”

The team created their sensors by transforming tin disulfide (SnS₂) — a yellowish-brown pigment generally used in varnish for gilding — into flakes just a few atoms thick. The large surface area of these flakes has a high affinity to nitrogen dioxide molecules.

The sensors operate by physically absorbing nitrogen dioxide gas molecules. Not only do they increase the level of sensitivity to accepted EPA standards, but they are said to outperform any other nitrogen dioxide sensing solutions on the market.

“The device shows high sensitivity and superior selectivity to NO₂ at operating temperatures of less than 160°C, which are well below those of chemisorptive and ion conductive NO₂ sensors with much poorer selectivity,” the researchers said in the journal ACS Nano. “At the same time, excellent reversibility of the sensor is demonstrated, which has rarely been observed in other 2D material counterparts.”

“The revolutionary method we’ve developed is a great start to creating a handheld, low-cost and personalised NO₂ sensor that can even be incorporated into smartphones,” Kalantar-zadeh concluded.

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