Electrical and VOC sensing properties of anatase and rutile TiO2 nanotubes

The dc electrical and volatile organic compound (VOC) sensing properties of TiO2 nanotubes in both anatase and rutile phases were investigated. TiO2 nanotube arrays were obtained in aqueous HF (0.5 wt.%) electrolytes by anodizing of Ti thin films that deposited on quartz substrates using thermal evaporation. Anodization was performed at 10 V in aqueous HF at 0 degrees C. Then the fabricated TiO2 nanotubes were annealed at 300 degrees C and at 700 degrees C under dry air for 5 h to obtain anatase and rutile phases, respectively. The TiO2 nanotubes were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM) as structural, and UV-vis spectrophotometer as optical. The current voltage characteristics of the nanotubes under dry air flow revealed that the conductivity of the sample with anatase phase was higher than that of the sample with rutile phase. The VOCs sensing properties of the nanotubes were investigated at 200 degrees C. It was found that the sensor response of anatase was higher than that of rutile for almost all VOC gases. On the other hand, the sensitivities of two sensors are the highest for isopropyl alcohol. (C) 2014 Elsevier B.V. All rights reserved.