الفهرس 
IntroductionOnly 14 pages are availabe for public view
 |  | from | 193 |  |  |
| | | from | 193 | | |
Abstract
The photocatalytic activity of TiO2 has aroused a broad range of research efforts and although TiO2 has a very high efficiency in utilizing ultraviolet light, its overall solar activity is very limited due to its wide bandgap (≈3.0−3.2 eV). This is a bottleneck for TiO2 to be applied in the areas ranging from visible-light photocatalysis and photovoltaics to photo-electrochemistry and sensors. Black titanium dioxide (BT) has been one of the most researched photocatalyst in recent years. Its ability to overcome the limitations of TiO2 through enhanced visible light absorption and reduced recombination of photogenerated charge carriers have gathered the attention of the scientific community. Numerous synthesis routes have been developed for black TiO2 owing to its superior activity as compared to white TiO2 in various applications such as (photo-electrochemistry, chemical sensors, energy storage, catalysis, etc.). Extensive studies have enabled understanding its superior activities and most studies reveal that defect species like Ti³⁺ and oxygen vacancies are responsible for the enhanced photoactivity.
Black titania has been incorporated with P-type metals to form heterojunction materials, thus overcoming the large white TiO2 bandgap drawbacks as well as the fast e--h+ recombination.
Black titania has been incorporated with P-type metals to form heterojunction materials, thus overcoming the large white TiO2 bandgap drawbacks as well as the fast e--h+ recombination.
The BT nanomaterials have been obtained by organic reduction protocol which intent to create enormous stable defects (Vo/Ti3+, Ti-H, Ti-OH or/and disordered surface) with unique properties that include optical and electronic properties, etc. For the first time through this fabrication route (imidazole reduction) a carbon nitride (C3N4) was also obtained with the BT.
Based on the foregoing, a number of materials have been prepared in the nanometer size, represented by:
1- Black TiO2/carbon nitride nanostructure (BT/C3N4).
2- CuO @ BT/C3N4.
3- Ag2O @ BT/C3N4.
4- Ag2S @ BT/C3N4.
The thesis includes five chapters:
The first chapter includes a brief introduction to the subject and literature revieԝ on our thesis study and the aim of the work.
The second chapter provides a theoretical revieԝ and calculation methods of surface area, crystallite size, energy gap, ac-conductivity and dielectric constant (ε`) at different frequencies, photovoltaic measurements, and hydrogen & oxygen evolution reactions (HER, OER).
The third chapter shows the materials used, synthesis methods including the preparation of black titanium dioxide and the different p-type materials based on black titanium dioxide. This chapter includes also experimental procedures and instrumental techniques that were used for samples characterization including X-ray diffraction (XRD), Fourier transform infrared (FTIR), transmission electron microscope (TEM), diffuse reflectance UV-Vis spectroscopy technique (UV-Vis DRS), surface texturing analysis (BET) X-ray photoelectron spectroscopy (XPS). Besides, the dielectric constant and ac-conductivity were measured at a constant voltage (1 volt) by using programmable automatic LCR bridge.
The Fourth Chapter includes the identification and affirmation of the prepared compounds composition of the BT/C3N4 nanopowders incorporated with the p-type oxide/sulfide in solar cell efficiencies.
The Fifth Chapter deals with:
i. The electrochemical measurements for instance cyclic voltammetry (CV), linear sweep voltammetry (LSV), electrochemical impedance spectroscopy (EIS), chronoamperometry and Tafel equation.
ii. Results and discussions of the BT nanopowders incorporated with the p-type oxide/sulfide toward the electrochemical H2O splitting.
The main results obtained are:
1) The BT/C3N4 catalyst was fabricated via an imidazole reduction route, but other p-Type (CuO, Ag2O, Ag2S) nanoparticles were prepared through a facile deposition hydrothermal method.
2) The p-Type nanoparticles @ BT/C3N4 were affirmed and characterized via XRD, FTIR, UV-Vis DRS, N2 sorptiometry, XSP and TEM techniques.
3) The most markedly was the Voc enhancement of the samples and their DSSCs besides the separation of the photogenerated charge carriers.
4) The measured solar cell performances of the synthesized photoelectrodes elaborated that the Ag2O/BT cell had the highest efficiency (6%) exceeding in sequence CuO/BT (5.6%), Ag2S/BT (no result) and BT (4.9%). The Ag2O/BT cell achieved the highest IPCE value of 40% in the visible light margin, whereas the Ag2S/BT electrode showed the lowest IPCE values.
5) As a prototype system, BT/C3N4 decorated by Ag2O possessed excellent stability in aqueous solution, highest IPCE% in the visible light margin of 500-750 nm, and superior photocarrier transport properties. The existence of Ti4+/Ti3+ and Ag+/Ag in Ag2O/BT brought great advantages via facilitating the photogeneration of electron/hole carriers besides enhancing their transfer rate and recombination control.
6) Linear sweep voltammetry (LSV) of the HER activity was tested in a neutral electrolyte. The HER overpotential values of BT, CuO/BT, Ag2O/BT and Ag2S/ BT equal 1.03, 0.99, 1.11, and 0.96V at -10 mA cm-2, respectively.
7) Incorporation of CuO is not only reduced the overpotential value into 1.0 V but also achieved the highest current density (89.23 mA cm-2). This demonstrated that CuO/BT was the best electrocatalyst.
8) Similarly, the overall water electrocatalysis of CuO/BT electrodes to produce a current density of 10 mA cm-2 required a voltage of 1.7 V under neutral and off-light conditions. This electrocatalyst exhibits superior efficiency due to lowering Tafel slope values for HER (-38.96 mV dec-1) and OER (102.2 mV dec-1). The CuO/BT electrode also presents excellent stability and superior electrochemical active surface area (ECSA) besides considerable amounts of appropriate active sites.
In a comparison of other previous studies, this study demonstrates confidently the superior features of the investigated samples that make them as a worthy constituent in solar cells and as efficient electrocatalysts in water fission.