Development of zinc oxide nanorods for hydrogen gas optical sensor

Abstract

Hydrogen (H2) gas is widely used as a clean fuel in various applications. The properties of H2 gas such as colourless, odourless and highly explosive gas require a practical and robust sensor to minimize the risk of explosion due to its volatile properties. The need to monitor H2 leakage detection at early stage to avoid accident is very important as it has a wide range of flammability in air (4-75%) by volume. H2 gas sensor was developed using etched-optical fiber coated with Zinc Oxide (ZnO). Single mode fiber has been used and it was etched by using hydrofluoric acid (HF) to enhance the evanescent field of the light propagates in the fiber core. The etched fiber was coated with ZnO nanorods via hydrothermal process by using seeding and growth solution. The sensing layer was characterized through Scanning Electron Microscopy (SEM), Energy Dispersive X-Ray (EDX) and X-Ray Diffraction (XRD) to verify the properties of ZnO. The sensing layer thickness is measured to approximately 1.5 micrometer. It is reported that the structural of nanorods can be controlled in terms of density, diameter, and length through a different growth duration which these parameters are important to the sensing mechanism of gas sensor. In this thesis, the developed sensor operating temperature was found to be 150°C that produces 6.36 dBm increase in response towards the 1% concentration of H2 in synthetic air. It is shown that the etching-optical fiber has increasing in the light-intensity output power with the increment of H2 concentration at 150 °C operating temperature. The sensor response and recovery times are 7 min and 3 min respectively for 0.25% of H2 concentrations at 150 °C. The etching optical fiber coated with semiconductor material has given significant impact on the optical-based application gas sensor. This work successfully contributes to the enhancement of sensitivity in a development of optical gas sensor compare to other previous work.