DEVELOPMENT AND CHARACTERIZATION OF METAL OXIDE NANOMATERIALS FOR HYDROGEN SULFIDE SENSOR

Abstract

Recently, many studies have demonstrated that metal oxide nanomaterials are excellent candidates for hydrogen sulfide resistive sensors. However, sensors based on metal oxide nanostructures suffer from several limitations such as i) requiring high operation temperature, ii) exhibiting a slow response and recovery time, iii) having a poor selectivity or sensitivity toward a specific gas, and iv) most importantly, they are not reliable on the long term. This study aims to overcome the mentioned drawbacks by using silver-loaded metal oxide-based nanomaterials to build gas sensors. For this purpose, nanomaterials with different dimensions (nanowires, nanoparticles, etc.) and dimensions will be employed to create the gas sensors. The performance of the sensors was evaluated towards toxic gases such as hydrogen sulfide. The nano porosity of the nanomaterials is expected to improve the sensing performance because of the increase in the specific surface area, allowing more gas molecules to adsorb on the surface of the materials. Silver and silver loaded tungsten oxide were used as a model system for two main reasons: i) it was reported to exhibit an enhanced sensitivity toward hydrogen sulfide and ii) due to the simplicity of the fabrication of the silver loaded metal oxide nanomaterials at low temperature and over a large-scale area. Two materials were synthesized, characterized, and tested for their gas response to H2S. The first is nanoporous silver oxide nanowires deposited by ultrasonic spraying and oxidized by oxygen plasma. Thin-film characterization is carried out using X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM), x-ray photoemission spectroscopy (XPS), and UV-Vis spectroscopy techniques. The obtained results indicate the formation of mixed mesoporous Ag2O and AgO NW thin films. Furthermore, it is confirmed that the crystalline size of the silver oxide is almost the same. The Ag2O phase of silver oxide appears after 300 seconds of oxidation under the same conditions, while the optical transparency of the thin film decreases as plasma etching time increases. The sheet resistance of the final film is influenced by the oxidation time and the periodicity of the plasma application. The gas testing showed low results or response to hydrogen sulfide. The second material is tungsten oxide, considered superior sensing material for hydrogen sulfide detection in the ambient environment. In this study, silver doped Tungsten oxide with various metal loading was prepared by microwave-assisted chemical route. The nanoparticle thin film was deposited on sensing electrodes to explore their gas and electrical properties. The morphology, crystal structure, and chemical state were examined using XRD, SEM, TEM, EDS, and XPS. The sensing properties of the sample were tested at different temperatures varying from room temperature to 200ºC. The Ag/WO3 showed enhanced H2S sensing abilities at very low temperatures (close to room temperature) and concentrations as low as 10 ppm compared to bare WO3. The results showed that Ag/WO3 sensors offer enhanced low-temperature sensing with reasonable response time, low operating power, and simple fabrication can be promising sensors for H2S sensing that can be utilized as wearable devices and in the industrial setting. To further study the material abilities, it was tested at very low concentrations of H2S with a unique experimental setup, the sensing properties, including sensitivity, selectivity, and stability, were investigated under different conditions. The material showed a response at as low as 0.25 ppm of gas concentration, with a high response reaching 80%. Moreover, it is selective for H2S against Ethanol, ammonia, and acetone. The sample's sensing characteristics were evaluated at various temperatures ranging from room temperature to 150oC and found that the response at RT is approximate to the optimum temperature response at (150oC). Also, the sensor was tested under humid conditions and showed sufficient response at room temperature. The research shows that Ag/WO3 sensors provide a high response at very low concentrations of H2S. Also, it enhanced sensing at low temperatures and in humid conditions sensing with a reasonable reaction time. These results allow for facile production of low operating power and portable gas sensing devices for industrial use in multi ambient conditions.

Date of Award	2022
Original language	American English
Awarding Institution	HBKU College of Science and Engineering