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

Although ZnO is studied intensively as a sensing material, there are limited reports available on aluminum-doped ZnO (AZO) as a NOx sensor. This paper reports selective NOx 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 NOx at lower operating temperature. It is also observed that as compared to gases such as SOx, HCl, LPG, H2S, H2, ammonia, alcohol and acetone it selectively detects NOx due to Al-doping. The amount of Al in ZnO during synthesis is varied between 1 and 10 wt%. Our sensor senses NOx 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 NOx involving oxygen ion adsorption and desorption on the surface of sensor has been suggested.