Select gas absorption in carbon nanotubes loading a resonant cavity to sense airborne toxin gases

A gas-sensing probe has been investigated that involves the use of microwave resonant circuitry to detect frequency shifts/Q-changes in a resonant microwave cavity caused by absorption of chemical/biological agents onto carbon nano-tubes (CNTs). Tests were made with single walled (SWNTs) to determine maximum selectivity of the probe. The ultimate goal is to accumulate a battery of test data for selected gases to establish a comprehensive inventory of potential gases that can be sensed with the apparatus. Additionally, it is anticipated that this work will result in a significant simplification of the design of the probe as well as the determination of an optimum frequency for probing with the cavity. Data presented in this work is offered as a demonstration of the feasibility of the instrument to detect non-toxic gases. As development continues, the device should be able to detect a wider range of gases including airborne toxins. Particle induced X-ray emission (PIXE) was used to characterize the impurities within the SWNTS to better understand the nature of the coupling of the microwave with the nanostructured material and ultimately to determine how impurities affect the sensitivity of the probe. (c) 2005 Elsevier B.V. All rights reserved.