Nanofibers and nanoporous metal oxides for gas sensing applications
Creators: name: Ab Kadir, Rosmalini
Publisher: name: RMIT University
Year: 2024
Subjects: classificationCode: 400899
subject: Electrical engineering not elsewhere classified
classificationCode: 400908
subject: Microelectronics
classificationCode: 400909
subject: Photonic and electro-optical devices, sensors and systems (excl. communications)

description: Air pollution is one of the greatest problems that the world facing is facing today. The World Health Organization (WHO) has provided air quality guidelines, which represent the most widely agreed and up-to-date assessments of air pollutants on human health, recommending stringent thresholds for air quality. This consequently signifies the need to develop gas sensors with the specifications that meet WHO targets. Additionally, gas sensors are also used in variety of other applications such as in many industrial surveillance and processes, automotive, aviation and food industries, medical analysis and diagnostics as well as homeland security and defense. It has been demonstrated that the key factors for developing efficient semiconducting gas sensors is to make use of selected metal oxides after engineering their morphologies and crystallographies. It is well-known that nanostructured metal oxides are generally superior in performance due to their high specific surface area. Hence, searching for the right nanostructured metal oxides with high specific surface area and controllable structures for effective gas sensing is an important research goal nowadays.<br><br>Many studies, however, have focused on creating nanofibers and nanopores as these morphologies are recognized to be amongst the most efficient for gas sensing applications. Due to the aforementioned justifications, the author of this PhD thesis became involved in the investigation of three different metal oxide nanofibers and nanopores metal oxides, which are tin oxide (SnO2) nanofibers, niobium oxide (Nb2O5) and tungsten trioxide (WO3) nanopores in both nanoporous and nanofibrious structures. There are many different types of gas sensors including those based on conductometric, Schottky and optical templates. In this research, the PhD candidate explored these three templates and investigated their performances when nanofibers and nanopores SnO2, Nb2O5 and WO3 sensitive layers are incorporated with them. To develop the nanostructured sensing films, the author chose electrospinning and anodization synthesis methods which are the most compatible for forming nanofibrious and nanoporous structures.<br><br>In the first stage, the PhD candidate demonstrated hydrogen (H2) gas sensors based on hollow and ﬁlled well-aligned electrospun SnO2 nanoﬁbers, operating at a low temperature of 150 °C.In the second stage of this research, the PhD candidate developed nanoporous Nb2O5 Schottky diode based ethanol (C2H5OH), H2 and methane (CH4) sensors. The sensing behaviours were studied in terms of the Schottky barrier height variations and properties of the metal catalysts. In the third stage, the PhD candidate focused on developing nanoporous Nb2O5 optical based H2 sensors. The compact nanoporous networks with high active surface areas demonstrated excellent absorbance changes at 100 °C with the response factor of 12.1 %. In the last stage, the PhD candidate explored Schottky diode based C2H5OH and H2 gas sensors fabricated via anodization of tungsten (W) foil to form nanoporous WO3 films. In summary, the PhD candidate believes that the studies carried out in the process of this research provided an in-depth vision regarding the fabrication and performance of nanofibers and nanoporous metal oxide based gas sensors.