Nitric oxide gas sensors with functionalized carbon nanotubes

Nitric oxide (NO) gas sensing with carboxyl functionalized single- and multi-walled carbon nanotubes (SWCNTs and MWCNTs) is demonstrated in this work. Stable solutions of the carboxylated nanotubes were made and then drop-cast on alumina substrates equipped with gold electrodes and also with platinum heater elements. The obtained resistive nanotube sensors were tested in a 2-point setup at different temperatures and NO gas concentrations up to 100 ppm in synthetic air and also in argon buffer. When exposed to NO, the conductivity of the sensors changed up to similar to 40% for SWCNTs and similar to 12% for MWCNTs; however, in the investigated regime, the response was found to be fairly independent on NO concentration. Though all sensors showed practically instantaneous gas response, the time needed for saturation (few tens of minutes) was found to be concentration dependent. 0 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.