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UBC Theses and Dissertations

Development, fabrication, and evaluation of UV-LED activated metal oxide semiconductor gas sensors for formaldehyde monitoring Ghorbani, Ghazal


Monitoring volatile organic compounds (VOCs) is necessary for indoor and outdoor environments due to their harmful effects on human health. Photo-activated metal oxide semiconductor (MOS) gas sensors have recently received significant attention for their detection of VOCs at room temperature due to their high sensitivity and low power consumption. However, these gas sensors suffer from several key drawbacks, including slow response time, inadequate recognition range and poor stability. In this study, photo-activated MOS gas sensors were developed to overcome some of the limitations of existing VOC gas sensors. Efforts were made to establish a suitable MOS for measuring formaldehyde as a model VOC and to enhance its stability throughout the sensing process. Using zinc oxide (ZnO) nanowires (NWs) as the sensing material showed restructuring caused by exposure to different concentrations of formaldehyde in the presence of UV radiation when its morphology and structure were analyzed. The sensing material, indium (Ⅲ) oxide (In₂O₃), also exhibited agglomerated nanoparticles (NPs). UV radiation in the presence of formaldehyde was found to play a critical role in sensing material restructuring and in its response inconsistency and instability. The elimination of UV radiation in the early stages of the response (e.g., first 5 min) avoided agglomeration of the sensing layer. Short-time UV exposure exhibited the potential to be applied in practical gas-sensing applications. Furthermore, a thin layer of Nafion was coated on the sensing layer to protect the structure of the UV-activated NPs from agglomeration. Sensor sensitivity was further improved by increasing the UV irradiance and decreasing the Nafion concentration. A 0.5 wt.% Nafion-coated In₂O₃ NP sensor showed a relatively high transient response of 0.15 when it was exposed to 25 ppm of formaldehyde under 2.56 mW/cm² irradiance. The gas sensor response slope within the first 1–5 minutes of the response curve was found to be a very good indicator of a 10 ̶ 50 ppm concentration of formaldehyde while avoiding agglomeration of the sensing material. The findings of this study can be incorporated into the development of UV-LED-activated gas sensors for which stable and fast response measurements of VOCs are required.

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Attribution-NonCommercial-NoDerivatives 4.0 International