Title: Effect of chemical oxidation on the gas sensing properties of multi-walled carbon nanotubes

Authors: Min Xu, Zhuo Sun, Qun Chen, Beng Kang Tay

Addresses: Department of Physics and Shanghai Key Laboratory of Magnetic Resonance, East China Normal University, No. 3663 North Zhongshan Road, Shanghai, 200062, PR China. ' Department of Physics and Shanghai Key Laboratory of Magnetic Resonance, East China Normal University, No. 3663 North Zhongshan Road, Shanghai, 200062, PR China. ' Department of Physics and Shanghai Key Laboratory of Magnetic Resonance, East China Normal University, No. 3663 North Zhongshan Road, Shanghai, 200062, PR China. ' School of Electrical and Electronic Engineering, Nanyang Technological University, 639798, Singapore

Abstract: The effect of chemical oxidation on the gas sensing properties of multi-walled carbon nanotubes (MWNT) is presented in this paper. The MWNT were chemically oxidised in a mixture of concentrated sulphuric and nitric acids. The oxidation time was varied from 4 h to 12 h. X-ray photoelectron spectroscopy was used to study the effect on the chemical composition of the nanotube surface. The results show that 8 h oxidation may be the favourite condition to introduce enough functional groups with inherent properties of MWNT being retained as much as possible. The different MWNT samples were deposited onto gas sensor substrates by drop coating method. The gas sensing properties of samples with different oxidation time for NO₂ and NH₃ were investigated at different concentration and temperature. The MWNT oxidised for 8 h showed the best gas sensing performance. As obtained MWNT did not show responsiveness below 30 ppm NO₂ while chemically oxidised MWNT can credibly detect NO₂ as low as 5 ppm at room temperature. Meanwhile, there was almost no response when as obtained MWNT in presence of 1000 ppm NH₃, while the oxidised MWNT showed quite good responsiveness at room temperature. Temperature dependant experiments showed that with the operation temperature increasing, the sensitivity increased obviously and the recovery process speeded up as well.

Keywords: multi-walled carbon nanotubes; chemical oxidation; oxidation time; gas sensors; nitrogen dioxide; ammonia; temperature; nanotechnology.

DOI: 10.1504/IJNT.2009.025311

International Journal of Nanotechnology, 2009 Vol.6 No.7/8, pp.735 - 744

Published online: 18 May 2009 *

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