Carbon monoxide is one of the most dangerous pollutants resulting from incomplete oxidation of carbon in combustion. According to the air quality standard, CO is required to have a concentration lower than 10 ppm. However, conventional gas sensor based on metal oxide thin film has serious limitation due to their poor sensitivity and high operating temperature. Recently, single-walled carbon nanotube (SWNT) network is reported to be a promising excellent gas sensor to detect oxidizing gases under room-temperature operation [1]. In this study, in order to develop an ultrasensitive CO sensor, SWNT network was functionalized with Pt nanoparticles and used as sensing material. An alumina substrate which is a platform of a conventional metal oxide thin-film sensor was used as a substrate for a growth of SWNT network. The SWNTs were grown by Fe/Al catalyst-assisted chemical vapor deposition [2]. Pt modified SWNT (Pt-SWNT) was fabricated by electron-beam evaporation of 0.5-2 nm of Pt over the SWNT network. Transmission electron microscope observation revealed that the metal deposition led to Pt particles decorating the side wall of the SWNT. CO was detected down to 1 ppm under room-temperature operation with a fast response. The sensor was recovered by using a heater set at the bottom of the substrate. The sensor response of Pt-SWNT to H2 was also investigated. Upon exposure to H2 with a high gas concentration of 5,000 ppm, the conductance of the Pt-SWNT exhibited a small change compared with that to CO with 100 ppm, implying a relatively good selectivity. These results show that surpassing performance of the conventional gas sensor, the Pt-SWNT acts as ultrasensitive CO detector down to 1 ppm with fast response under room-temperature operation [3]. This work was partly supported by a Grant-in-Aids for Scientific Research from the Japan Society for the Promotion of Science, and Kochi Industrial Promotion Center. One of the authors (W.W.) acknowledges the support from the Japan Society for the Promotion of Science.
[1] W. Wongwiriyapan et al., Jpn. J. Appl. Phys. 44(2005) L482.
[2] W. Wongwiriyapan et al., Jpn. J. Appl. Phys. 44, (2005) 8227.
[3] K. Ihokura et al., The Stannic Oxide Gas Sensor: Principles and Applications (CRC Press, Boca Raton, 1994). |