Toxic Gas Sensor Monitors Nitrogen Dioxide With High Sensitivity, Uses Nanobranch Material To Improve Detection Limit

The emission of toxic gases has been on the rise in the past decades due to industrial developments. Being major air pollutants, these gases such as nitrogen dioxide must be monitored to protect human health.

Challenges in Monitoring Toxic Gases

In the past decades, the rapid growth of industry and road transportation has led to the increased emissions of toxic gases in the atmosphere. These gases lead to air pollution which damages the brain and impairs a person's cognitive ability. In particular, nitrogen dioxide causes respiratory diseases and environmental damages such as acid rain.

Nitrogen dioxide is a toxic gas produced by the high-temperature combustion of fossil fuels and is emitted through automobile exhaust or factory smoke. In the US, the Environmental Protection Agency has set the national ambient air quality standards (NAAQS) for nitrogen dioxide at a level of 53 parts per billion. This means that highly sensitive sensors are needed to accurately detect toxic gases at extremely low concentrations.

Most laboratories and factories adopt semiconductor-type sensors for monitoring nitrogen dioxide. However, such types of devices have low response sensitivity which makes them unable to detect toxic gases that may even be perceptible to the human nose. Increasing their sensitivity will mean consumption of a lot of energy since they need to operate at high temperatures.

Novel Toxic Gas Sensor

To address this challenge, experts from Korea Research Institute of Standards and Science (KRISS) developed a toxic gas detector with the highest sensitivity in the world. Their findings are discussed in the paper "MOCVD of Hierarchical C-MoS2 Nanobranches for ppt-Level NO2 Detection".

This device is a next-generation semiconductor-type toxic gas sensor made from advanced materials with improved performance and usability. With its remarkable sensitivity to chemical reactions, the newly-developed sensor can detect nitrogen dioxide 60 times greater than previously reported semiconductor-type sensors. Additionally, it only consumes minimal power at room temperature, while its optimal semiconductor manufacturing process allows large-area synthesis at low temperatures.

The key to this advanced capability lies in the molybdenum disulfide nanobranch material designed by KRISS. While conventional molybdenum disulfide has 2D flat structure, the novel material was synthesized in a 3D structure that resembles tree branches.

The experimental demonstration of the KRISS Semiconductor Integrated Metrology Team revealed that the toxic gas sensor can detect nitrogen dioxide in the air at concentrations as low as 5 parts per billion. Since the calculated detection limit of the sensor is 1.58 parts per trillion, this marks the highest level of sensitivity in the world.

This novel technology can be applied to various fields such as electrolysis catalyst research and detection of residual gases from semiconductor manufacturing processes. It also has the ability to adjust the carbon content in the raw material during the stage of material synthesis.

This enables the sensor to detect gases other than nitrogen dioxide, like the residual gases emitted during the semiconductor manufacturing process. Moreover, the remarkable chemical reactivity of the sensor can be utilized to improve the performance of electrolysis catalysts for hydrogen production.