Jan 31, 2013
Hybrid nanostructures detect 1 ppm carbon monoxide
Carbon monoxide (CO) is a toxic and flammable gas that can cause serious damage if inhaled or allowed to explode. To avoid potential harm, it is crucial to monitor and detect the concentration of CO in air in a highly sensitive and responsive manner. However, the detection of CO at room temperature has remained challenging, mainly due to the reduced reactivity of CO at low temperatures. Hybrid nanostructures based on SWNTs are promising for detecting low-concentration CO at ambient conditions thanks to the extremely high surface-to-volume ratio and unique electrical properties of the SWNTs, and synergetic effects that occur within SWNT-nanoparticle hybrids.
Presenting their results in the journal Nanotechnology, researchers at the University of Wisconsin-Milwaukee in the US have recently demonstrated a platform that can detect CO with high sensitivity at room temperature. The sensing device was constructed with SWNTs that were assembled on gold interdigitated electrodes via dielectrophoresis. Hybrid structures were then formed by decorating the SWNTs with SnO2 nanoparticles through an electrostatic force directed assembly (ESFDA) process using a mini-arc reactor.
In the study, the sensitivity of the device was defined as the ratio of the resistance change in the target gas to the sensor resistance in dry air. The highest sensitivity obtained by the team was ~0.27. Interestingly, this value was boosted to ~0.67 after subjecting the sensor to an electrical breakdown (high current treatment). The detection limit of the group’s sensors was determined to be ~1 ppm at room temperature.
Modeling the system
In addition to the experimental work, the scientists also proposed a theoretical model to explore the relationship between the sensitivity of the device and the concentration of the target gas. Their analysis builds on the empirical power-law model that is widely used in the gas sensing community. The approach links sensitivity to fundamental quantities such as the amount of charge transferred per adsorbed gas molecule, the adsorption energy, and the target gas concentration.
The proposed model can help to interpret sensing data and is also a useful design tool.
More information can be found in the journal Nanotechnology.
About the author
Yang Zhang is a postdoctoral research associate in the group of Prof. Junhong Chen in the Department of Mechanical Engineering at the University of Wisconsin-Milwaukee, Wisconsin, US. He is currently exploring novel gas sensing systems based on carbon materials, and understanding the physics behind these systems.