Graphene-based gas sensor
doi:10.1038/nindia.2012.75 Published online 18 May 2012
Researchers have designed a new type of sensor that can detect minute traces of nitrogen dioxide, a polluting gas. The sensor, made from a nanocomposite of graphene and tungsten oxide, will be very useful in reducing the amount of nitrogen dioxide produced by industry.
Graphene has a larger surface area than carbon nanotubes, thus offering additional improvements. The surface of graphene is also extremely sensitive to the attachment or detachment of gas molecules.
To explore the gas-sensing potential of graphene, the researchers first synthesized graphene oxide and then reduced it to graphene. They added different amounts of graphene (0.2, 0.5 and 1.0 wt%) to tungsten oxide, yielding three different nanocomposite samples. Next, they smeared layers of five different samples — graphene only, pure tungsten oxide and the three nanocomposites — on an alumina sensor substrate.
The researchers studied the gas-sensing properties of each layer at temperatures in the range of 200–300°C. At room temperature, they carried out gas-sensing measurements for different concentrations (1, 5, 10 and 20 ppm) of nitrogen dioxide in air.
The sensor based on tungsten oxide–graphene (0.2 wt%) exhibited a good response even at gas concentrations below 5 ppm. The sensor response rose further with an increase in the amount of graphene (0.5 wt%). At room temperature, the tungsten oxide–graphene sensor's response to nitrogen dioxide was nearly three times higher than that of a pure tungsten oxide layer.
The researchers say that a graphene concentration of 0.5 wt% in the nanocomposite layer is optimum for gas-sensing applications.
The authors of this work are from: Physics of Energy Harvesting, Sophisticated and Analytical Instruments, and Apex Level Standards and Industrial Metrology, National Physical Laboratory, New Delhi, India.