الفهرس | Only 14 pages are availabe for public view |
Abstract H2S gas is considered a silent killer which causes sudden death in fields where this gas occurs naturally. Although H2S gas sensors are applied, they are generally in the rigid form and hardly meet the requirements of flexible electronic devices, also suffer from high power consumption, and relatively long response time. Therefore, the fated risks of H2S gas and the demand for a higher performance and lower power consumption sensors urge the search of new materials which are capable of fulfilling all these demands. The main objectives of this thesis are: Designing and fabricating chemiresistive H2S gas sensors based on metal oxide (MOx) nanomaterials; CuO, SnO2 nanoparticles (NPs) and their nanocomposites (NCs) doped with the conductive polymer Polypyrrole (Ppy) by synthesizing the pure metal oxide nanoparticles CuO and SnO2 via the Co-precipitation method as an initial step followed by the doping process for the preparation of polymer / metal oxides nanocomposites as H2S gas sensing materials through insitu-polymerization approach. 1- Ppy / CuO NC 2- Ppy/ SnO2 NC 3- Ppy/CuO-SnO2 NC 4- Ppy/CuSnO3 NC The structures of all synthesized materials have been verified by; Fouriertransform infrared spectroscopy (FTIR), X-ray diffraction (XRD) , High resolution electron microscopy (HRTEM), Scanning electron microscopy (SEM) , Dynamic light scattering (DLS) , thermo gravimetric analysis (TGA), and gel permeation chromatography (GPC), which all agreed with assigned structures. The thesis involves detecting the sensing materials responses towards different concentrations target gas H2S concentrations. The testing process divided into two methods: 1- The conductometric Interdigited electrode based method which is depending on coating the interdigited electrode by the prepared sensing materials and measuring its response throughout electrical resistance changes by Keithley electrometer. 2- The MEMS based method referring to the best performance gas response material from the first method. It was shown that the best response to the different concentrations of H2S gas was the Ppy/CuO-SnO2 nanocomposite by 68% followed by Ppy/SnO2 then Ppy/CuSnO3 nanocomposite and Ppy/CuO nanocomposite at room temperature. The thesis consists of three chapters as follows: Chapter one: Introduction This chapter discusses some facts and information related to the thesis. It begins with providing some facts about H2S gas, like sources and risks, the general background of H2S in the petroleum industry, its harmful effects and methods of detection, the gas sensor history, its fundamentals and sensing mechanism. Then, it presents a variety of applied materials that have been used in the fabrication of H2S gas sensors like semiconducting metal oxides (SMOx), the properties of NPs related to the process of sensing and preparation methods, the techniques of characterization and their use in gas sensing. Also, great attention is paid to the polymers and their nanocomposites. The electrochemical sensor based polymer and metal oxides nanocomposites and its fabrication methods. The technology of Micro Electro Mechanical Sensors (MEMS) and its application in gas sensing also discussed. Finally, the proposed alternative sensing materials that will be used in this thesis and are expected to be H2S gas sensors. Chapters two: Experimental work This chapter discusses the steps of fabricating the sensing materials. It provides the detailed processes of synthesis the CuO, SnO2 NPs also the preparation of their Spinal CuSnO3 and composite CuO-SnO2 forms. Then, it shows the production of the sensing materials where these nanoparticles are separately incorporated within a conducting polymer Ppy; followed by the methods that have been used to characterize the NPs, NCs and the sensing material. Finally, the device fabrication and experimental setup are discussed. 1- The synthesis of sensing materials; MOx NPs via the co-precipitation method, Ppy and Ppy/MOx NCs via insitu-polymerization technique. The resulting materials were characterized by X-ray diffraction (XRD) to elucidate the crystallinity of the materials and calculating the particle size from Scherrer formula, transmission electron microscope (TEM) to identify the shape of the synthesized materials and to determine the particle size, Fourier-transform infrared (FT-IR) to identify the resulting materials, the particle size distribution by Dynamic Light Scattering (DLS). The Scanning Electron Microscopy (SEM) to confirm the nanocomposite formation. Gel permeation chromatography (GPC) measurements for calculating the polymer molecular weight. Thermo gravimetric Analysis (TGA) for studying the thermal stability of the prepared materials. 2- The testing steps were carried on two different systems, Conductometric and MEMS techniques. 3- Chapters two: Results and Discussion The synthesized sensing materials were characterized to study their structural and morphological characteristics. Then, the gas sensing performance and gas sensing mechanism were investigated. We briefly tried to introduce a mechanism for the polymer nanocomposites mechanism of sensing towards H2S gas on the basis of electrochemistry as a type of electrochemical sensors. The results of this study showed that the proposed sensors possess good sensing properties. The best response among all the fabricated and tested sensors towards H2S gas with different concentrations at Room temperature was recorded by the polymer nano composite Ppy/CuO-SnO2 with 68%. The detection limit was between 100-1000 ppm for all tested sensors. The results showed a reasonable average response time of 3 seconds, which was in good agreement with previously reported work in the field of H2S gas sensing applications. The proposed H2S gas sensor using MEMS technique tested under (40, 100 ppm) gas concentrations at ambient conditions. The two selected sensing materials referring to the conductometric method was Ppy and Ppy/CuO-SnO2 NC and the response results also confirmed that Ppy/CuOSnO2 NC has the best sensitivity with sensing time of 23 seconds under 40 ppm and 10 seconds under 100 ppm H2S concentration at room temperature. |