Preparation And Gas Sensing Properties Of The Vanadium Oxide Nanotubes

With the development and progress of our socio-economic and the gradual improvement of the living standard of the people, the increasing concern over safety on industrial sites and in homes has generated great interest in reliable gas detection, which promotes the research on the gas sensing materials at the same time. One-dimensional (ID) nanostructure materials have been reported to produce new semiconductor gas sensors for higher surface-to-volume ratio and the nano-size which is likely to produce a complete depletion of carriers inside the materials, for which the one-dimensional nanostructure materials have high sensitivity and fast response time and is suitable for gas sensor. ID vanadium oxides have been reported for their interesting properties such as gas sensing, electrochemical, and optical properties which is due to unique layered structure of the vanadium oxides. The tubular morphology of the vanadium oxide is particularly attractive since it provides access to the three different contact regions:inner and outer surface as well as the tube ends, and these make the ID vanadium oxides nanotube likely to be good sensor materials. So it is great significance and valuable to study the gas sensing properties of the ID vanadium oxides nanotube.Vanadium oxide nanotubes (VONTs) were synthesized via one-step hydrothermal way, and then the vanadium oxides nanotubes coated with metal oxide MOX (M=Fe and Ti) have been prepared by second hydrothermal reaction. Therefore, it is significant to research the preparation, microstructure and gas sensing properties of vanadium oxide nanotubes.1. The VONTs were prepared by hydrothermal treatment using V2O5power, distilled water and dodecylamine/ethanol solution. At the same time, the impact of the PH value of the V2O5nH2O/dodecylamine ethanol suspension (precursor solution) and the hydrothermal reaction time on the formation of the VONTs also have been studied. It revealed that the longer hydrothermal reaction time is conducive to the formation of the VONTs, and the high PH value of the precursor solution will hinder the farmation of the VONTs.The sensitivity to ethanol vapor of the sample with three days of hydrothermal treatment had been studied. The length of the VONTs is2-4μm, and the inner diameter and outer diameter is40-50nm and100-120nm, respectively. The prepared VONTs sensors exhibit excellent sensing sensitivity and superior recovery property in detecting ethanol vapor, the VONTs could be able to detect lppm ethanol with15-50s at80℃. The response to the ethanol vapor and NO2gases confirms that the samples are of p-type behavior at80℃, which is associated with the presence of the protonated amine molecules in the VONTs. The sample changes to n-type behavior at260℃arising from the decomposition of the protonated amine molecules and releasing the electron to the nanotubes. 2. Metal oxide MOX(M=Fe and Ti) surface modified VONTs have been prepared by second hydrothermal reaction.It revealed that the morphology and structure of the vanadium oxide didn’t changed after the second hydrothermal reaction, and the samples coated with metal oxides are still a nanotube structure. And the sensitivity (S) of the samples to the ethanol vapor has been significantly improved by coating the metal oxide on the surface of the vanadium oxide nanotubes, which is proved that the modification to the vanadium oxide nanotubes is successful.