Nitrogen dioxide is toxic to humans when inhaled. Unfortunately, our noses get anaesthetised when exposed to low levels of nitrogen dioxide. This prevents us from sensing the otherwise acrid gas, creating a possibility for overexposure with harmful effects on health. This may lead to poisoning of the lung, which in some cases might prove to be fatal.
Nitrogen dioxide is a reddish-brown gas found where fossil fuels are utilised as an energy source. The elevated temperatures during combustion cause the nitrogen in the atmosphere to react with oxygen to form nitrogen dioxide. Since we use fossil fuels every single day, nitrogen dioxide detectors are vital for monitoring the levels of the gas in the ambient air.
Recently, nanoscale materials such as carbon nanotubes and graphene have been found to be very suitable for sensing applications, because of their large surface to volume ratio. Graphene-based gas sensors can even detect gaseous species down to single molecular level.
Graphene is a thin layer of pure carbon, where the atoms are bound together in a honeycomb like pattern. Three dimensional graphene networks have been found to be easy to fabricate and are known to have really commendable sensor performances. They are also available at a lower manufacturing cost than other material fabricated at the nanoscale.
A team of researchers lead by Dr. Abha Misra from the Indian Institute of Science with expertise in the fields of nano-science, instrumentation, material science, and physics have developed this three-dimensional graphene microstructure to be used as sensors for detecting nitrogen dioxide. They have devised an extremely light foam by freeze-drying to achieve even 0.2wt% of graphene oxide in air.
“The graphene based sensors works on the principle that charge transfer takes place between graphene foams and adsorbed gas molecules. This changes the resistance of the foams and hence their electrical conductivity. By measuring these changes in electrical conductivity and correlating them with the levels of ambient nitrogen dioxide, a system to monitor the gas levels can be set up” mentions Anwesha Mukherjee, a contributing student.
“We show a much better response of ultralight graphene foams for NO2 sensing as compared to available results in the literature,” adds Swetha Jayanthi, one of the authors. This nanoscale graphene based foam boasts a change in sensitivity of 20% for a 100 ppm (parts per million) increase in the concentration of the gas, over its best contender which is reported to have a sensitivity of 12.5% for 200 ppm concentration increase.
“These ultralight and highly sensitive three-dimensional structures can essentially pave the way for future highly efficient sensing systems,” remark the researchers proudly in their manuscript, having set up new standards for nitrogen dioxide detection.
About the Authors:
Swetha Jayanthi is a PhD scholar at the Centre for Nano Science and Engineering. Anwesha Mukherjee is a PhD scholar at the Department of Instrumentation and Applied Physics. Prof. Kaushik Chatterjee is from the Department of Materials Engineering. Prof. A.K. Sood and Prof. Abha Misra are from the Department of Physics. They are all affiliated to the Indian Institute of Science.
Their paper is going to be published in January 2016 and is available in advance online:
http://www.sciencedirect.com/science/article/pii/S0925400515302197
Contact: abha@isu.iisc.ernet.in (Abha Misra)