Low temperature synthesis and NO_x sensing properties of nanostructured Al-doped ZnO

Abstract

Although ZnO is studied intensively as a sensing material, there are limited reports available on aluminum-doped ZnO (AZO) as a NO_x sensor. This paper reports selective NO_x sensing characteristics of Al-doped ZnO synthesized in the form of porous pellets sintered at 350 °C. The salient feature of our experimental results is that our sensor can detect small concentrations of NO_x at lower operating temperature. It is also observed that as compared to gases such as SO_x, HCl, LPG, H₂S, H₂, ammonia, alcohol and acetone it selectively detects NO_x due to Al-doping. The amount of Al in ZnO during synthesis is varied between 1 and 10 wt%. Our sensor senses NO_x concentration as low as 20 ppm at 100 °C with a %response of 11 and a %response of 740 at 300 °C for 1 wt% Al. Of all the compositions with Al-doping, 1 wt% is found to give best results. Sensing experiments carried out at 350 °C, however, do not show any significant improvement in the gas sensing properties. The phase contents and lattice parameters were determined by XRD and the average particle size was obtained using Scherrer formula. A probable mechanism for sensing NO_x involving oxygen ion adsorption and desorption on the surface of sensor has been suggested.