Room Temperature Gas Sensing Using Pure and Modified Metal Oxide Nanowires

Abstract

Recently, various quasi 1D metal oxide semiconductor nanostructures (nanorods, nanowires, nanotubes, nanobelts) of various binary oxides have been found to be excellent materials for gas sensing. However, some of the sensitive gas sensors can work only at elevated temperatures. The sensing performance can be further improved when these oxides are doped with noble metal nanoparticles and form hetero-junction with other oxides, especially different types of metal oxide. These modifications can substantially change the surface properties as well as electronic properties due to their enhancement of the depletion layer at the metal nanoparticle-metal oxide nanowire and homo/hetero-interfaces. The objective of this dissertation study is to investigate the sensing performance of WO3, ZnO, NiO and TiO2 nanowires towards various air pollutant gases such as NH3, NO2, H2S and CO at room temperature. The sensing performance of pure metal oxide nanowires are further improved by doping these nanowires with noble metal nanoparticles and through the formation of n-p hetero-junction of two dissimilar oxides. Based on this study, it was found that pure ZnO and NiO nanowires show a high sensitivity and the best selectivity performance towards the ppm level NO2 (1 ppm) with respect to other interfering gases. On the other hand, both WO3/Ag and WO3-NiO gas sensors show enhanced sensing and highly selective performance towards H2S (~10ppm) at room temperature. Additionally, sensor response and recovery become faster with WO3/Ag than pure WO3 nanowires. The plausible reasons for such improvements with these surface modifications are discussed. This study provides a scientific foundation to engineer practical room-temperature gas sensors with enhanced performance.