Studies on alcohol sensing mechanism of ZnO based gas sensors

Nanosized ZnO powder was synthesized by using a chemical precipitation method, and loaded with different dopants through impregnation. The as-prepared ZnO powder was characterized by XRD, and TEM. The characterization results show that the as-prepared sample is wurtzite polycrystalline ZnO, the mean grain size is 30-40 nm, and there are three types of adsorbed oxygen (O-2(-), O-2(2-), and O2-) on the surface of the sample. The as-prepared ZnO powder shows excellent gas responses to alcohol and acetaldehyde, but no response to ethene. The sensing mechanism of ZnO was further studied with the help of gas chromatography (GC) associated with a fixed-bed reactor. The studies show that acetaldehyde, carbon dioxide and water are the only oxidation products of C2H5OH over ZnO. The gas response to C2H5OH is strongly dependent on the conversion ratio of CAM to acetaldehyde. In addition, among all the dopants tested, Ru is the optimal dopant which can increase the response to C2H5OH, but cannot increase the conversion ratio of C2H5OH to acetaldehyde. Thus we suggest that the gas sensing mechanism of ZnO to C2H5OH is the mode controlled by chemisorption of negatively charged oxygen, and the sensitizing role of Ru in the ZnO sensor belongs to the electronic sensitization mechanism. (C) 2008 Elsevier B.V. All rights reserved.