الفهرس 
Chapter IOnly 14 pages are availabe for public view
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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.