Carbon nanotube (CNT) gas sensors for emissions from fossil fuel burning

Fossil fuels endow wide applications in industrial, transportation, and power generation sectors. However, smoke released by burning fossil fuels contains toxic gases, which pollutes the environment and severely affects human health. Carbon nanotubes (CNTs) are potential material for gas sensors due to their high structural porosity and high specific surface area. Defects present on the CNT sidewalls and end caps facilitate adsorption of gas molecules. The chemical procedures adopted to purify and disperse carbon nanotubes create various chemical groups on their surface, which further enhance the adsorption of gas molecules and thus improve the sensitivity of CNTs. Present review focuses on CNT chemiresistive gas sensing mechanisms, which make them suitable for the development of next generation sensor technology. The resistance of carbon nanotubes decreases when oxidizing gas molecules adsorb on their surface, whereas, adsorption of reducing gas molecules results in increasing the resistance of CNTs. Sensing ability of carbon nanotubes for the gases namely, NO, NO2, CO, CO2 and SO2, released on burning of fossil fuels is reviewed. This review provides basic understanding of sensing mechanisms, creation of adsorption sites by chemical processes and charge transfer between adsorbed gas molecules and surface of CNTs. In addition, useful current update on research and development of CNT gas sensors is provided.