Dependence of gas sensing properties in ZnO nanofibers on size and crystallinity of nanograins
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pendence of gas sensing properties in ZnO nanofibers on size and crystallinity of nanograins Sun-Woo Choi, Jae Young Park, and Sang Sub Kima) School of Materials Science and Engineering, Inha University, Incheon 402-751, Republic of Korea (Received 21 February 2011; accepted 13 June 2011)
We demonstrate that the size and crystallinity of grains in individual ZnO nanofibers greatly influence their sensing properties for CO. The sensing properties, including sensitivity, response and recovery times of a sensor fabricated with ZnO nanofibers composed of large grains are much superior to those of a sensor fabricated with nanofibers of small grains. The crystallinity, improved by the longer calcination time, is likely to be responsible for the higher sensitivity in the largegrained nanofibers. The facilitated occupancy and desorption of CO molecules at grain boundaries in the large-grained nanofibers are the most probable causes of the shorter response and recovery times in detecting CO, respectively. This work suggests not only that electrospinning-synthesized ZnO nanofibers hold promise for realizing sensitive and reliable gas sensors but also that the size as well as the crystallinity of the grains existing in individual nanofibers need to be optimized to obtain the best sensing properties.
Potential applications of oxide nanofibers are being widely exploited because of these fibers’ advantages of large surface area and low-cost production.1–3 These are valuable characteristics for sensor and catalyst applications in which surface-controlled reactions are critical.4–6 Such nanofibers were first synthesized a few decades ago and, since then, nanofibers of various metal oxide materials have been prepared and characterized, and their potential applications in many areas have been demonstrated.7–9 Very recently, the growth behavior of nanograins in ZnO nanofibers synthesized by electrospinning has been investigated by the current authors.10 According to the results, individual nanofibers consist of nanograins. The nanograins coalesce and grow under higher calcination temperatures and longer calcination times. The size of the nanograins is likely to determine all of the physical and chemical properties of the nanofibers. One of the important applications of oxide nanofibers is as gas sensors. Therefore, it is interesting to study how the size of nanograins influences the gas sensing properties. In this study, the effects of the size of nanograins in ZnO nanofibers on gas sensing properties for CO were investigated. We found that ZnO nanofibers with large nanograins show sensing properties superior to nanofibers with small nanograins. ZnO nanofibers were synthesized by the electrospinning method. The synthesis procedure and nanofiber a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2011.209 1662
J. Mater. Res., Vol. 26, No. 14, Jul 28, 2011
http://journals.cambridge.org
Downloaded: 28 Jun 2014
microstructures are described in detail in the previous work.10 Two different nanofibers that were calcined fo
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