Synthesis and fundamental understanding of metal oxide nanostructures for gas-sensing applications

Abstract

Gas sensors are indispensable aspects of our life as it warns us about the dangerous gases in our environment. Semiconducting oxide gas sensors are by far the most popular type of sensors, because of their simple processing and low fabrication cost. The early metal oxide-based sensor materials however often exhibit several undesirable characteristics, such as poor selectivity, sensitivity to moisture, long-term signal drift and, slow response time. Hence, the development of fast-responding gas sensors with high sensitivity and selectivity is highly desirable. The introduction of nanotechnology has attracted large interests in gas-sensing research, largely because nanoscale particles offer a larger high surface area to volume ratio and enhanced functionalities compared to bulk particles. In particular, the synthesis of metal oxide nanostructures with controlled morphology is highly attractive because the properties of nanostructure depend not only on their composition, but also on their structure, phase, shape, size, and size distribution. Many efforts have been carried out to improve the „3S‟: sensitivity, selectivity, and stability of semiconductor gas sensors by utilizing metal oxide nanostructures. However, some challenges still exist in both synthesis and fundamental understanding of the gas-sensing mechanism of nanoscale metal oxides. This thesis aims to explore the use of nanostructures based on n-type semiconducting oxides as gas sensor materials for the detection of VOCs and to develop different ways to enhance the sensitivity of these metal oxide nanostructures through means of structural iii control, surface engineering and introduction of additives such as metal oxides and noble metals. Our research method involves the use of various microscopy, diffraction, and spectroscopy techniques to characterize the achieved metal oxide nanostructures or nanocomposites. To gain a further insights understanding of the metal oxide/gas interactions during the sensing process, it is important to use multi-scale theoretical methods validated by experimental techniques. The findings will benefit the design and construction of gas sensors with desirable properties/performance (sensitivity, selectivity and stability) for potential applications in environmental monitoring and detection.