الفهرس 
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Abstract
Tamer Mahmoud Ahmed Mahmoud Khedr: “Development of Novel Solar Light-Activated Photocatalysts for Clean Energy Production and Degradation of Emerging Contaminants”. This thesis contains four chapters, 272 Pages, 39 Tables, 123 Figures, 264 References, 2022.
Energy and water crisis are considered as the biggest threats to human and even every living organism worldwide. Rapid population growth and technological advances are the main reasons for these problems. Solar-light-activated heterogeneous photocatalysis (green, sustainable, and clean technology) has attracted much attention to address these problems. However, this technology is suffering from some limitations; principally fast electron-hole recombination and low solar-light absorption ability. Therefore, great efforts have been paid to the development of novel solar-light-responsive heterogeneous photocatalysis for the generation of a clean and green energy source (H2) and for removing organic pollutants from water to contribute to facing energy and water problems.
This study provides green strategies for the synthesis of novel visible-light-responsive photocatalytic systems (having an effective charge separation efficiency and high visible-light harvesting ability) for enhanced photocatalytic H2-fuel generation and removal of emerging pollutants from water. This thesis is divided into four main chapters, i.e., introduction and objectives of the study, literature review, experimental and methods, and results and discussion.
Chapter 1 “introduction and objectives of the study” focuses on the problem statement of the energy and water crisis, as well as the objectives and significance of this work. Energy and water crisis are the most serious threats to human life and property worldwide. Energy and water, being closely linked,
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are the primary sources of life on Earth. The global energy and water crisis include scarcity, depletion, increasing demand, rising cost, and increasing environmental pollution. The rapid increase in the human population, industrialization and globalization are the main causes for the global energy and water crisis, and therefore it is proposed that most of the problems and wars in the world arise from energy and water lack/or control over their sources.
Recently, global energy consumption has witnessed exponentially rising, and it has been projected that the world energy uses may rise by 28% by 2040, and therefore available fossil fuels (the primary energy resource worldwide) reservoirs would be exhausted in future, with increasing the energy demands. Meanwhile, the rapid increase in the energy consumption needs combustion of large amounts of fossil fuels, and hence releasing a huge amount of greenhouse gas, CO2, which is the main reason for global warming, several environmental problems (water, air, and marine pollution, acid rain, stratospheric ozone depletion), and harmful impacts on humans and animals. Therefore, great attention has been devoted to developing alternative and sustainable renewable energy resources (solar, wind, hydro, current, geothermal, biomass, wave, tidal, hydrogen) to provide clean energy and overcome global warming and environmental pollution.
Hydrogen (H2) has been extensively recommended as a green and promising renewable energy source in the future because it is a carbon-free, renewable, eco-friendly, and clean fuel, having a high energy density, and could be easily stored and transported over long distances, compared with non-renewable hydrocarbon fuel (i.e., fossil fuel). With the continuous development of hydrogen technology (i.e., production, storage, and application), it has been anticipated that H2 would be an energy centre in the near future; just like
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electricity, today is. However, the current technologies used for the production of the H2-fuel are facing a significant challenge to meet sustainable global development. To address these issues, great attention has been paid to developing heterogeneous photocatalysis for boosted photocatalytic H2 generation.
Water is the most precious natural resource on our planet. Even though about 70% of the Earth’s surface is covered by water, the freshwater represents only 2.5% of the total amount of water, among which only less than 1% is available for human use. With rapid population growth, water demands and pollution are increasing day by day, and it is expected that more than 50% of the world’s population would suffer chronically water shortage by 2050. Therefore, scientists proposed that the removal of water pollutants would contribute to solving these issues. Emerging contaminants (ECs) have been recently recognized and detected as one of the most dangerous water pollutants (existing with low concentrations, ranging from ng L-1 to μg L-1). Among them pharmaceuticals (e.g. DCF) and cyanotoxins (MC-LR) are considered the most popular and most toxic. The presence of ECs in water has become a serious threat to humans, animals, plants and even microorganisms. Therefore, several physicochemical and biological technologies “conventional technologies”, such as adsorption, filtration, flocculation, sedimentation, coagulation, disinfection, chemical oxidation, chlorination, and microbial degradation, have been used for the removal of ECs from water. However, the practical applications of these technologies are limited by some drawbacks, such as low processing efficiency, high energy consumption, high cost, high processing time, and formation of toxic sludge, metabolites, and byproducts. Therefore, the development of heterogeneous photocatalysis as an alternative technology for the efficient removal of ECs has attracted much attention these days.
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Therefore, the aim of this thesis is to develop simple and cost-effect strategies to fabricate high efficient heterogeneous photocatalytic systems having high solar-light absorption efficiency and redox-ability, and high efficiency for charge carriers’ separation, for an enhanced photocatalytic H2-fuel generation and degradation of emerging pollutants to stand up to the energy and water crisis. Accordingly, the objectives of this thesis could be divided into four:
1) To overcome the rapid electron-hole recombination in TiO2, the binary-phase (A/B) mesoporous TiO2 photocatalyst (having different A/B ratios) was tailoring synthesized by a facile hydrothermal method through two approaches; effect of NH4+, Na+, -OH, and different GLY concentrations; and effect of different initial preparation pH values.
2) To tackle the fast charge recombination and improve the solar-light harvesting ability of titania, the C-N-S tri-doped binary-phase (A/B) mesoporous TiO2 photocatalyst using thiourea as a doping source.
3) To overcome the rapid recombination of charge carriers and enhance the solar-light harvesting ability of g-C3N4, the sulfur-doped 2D mesoporous g-C3N4 photocatalyst was prepared by a simple gas-templating thermal-polymerization method.
4) To address the limitations of single-component photocatalyst, the direct Z-scheme of 2D/2D S-doped g-C3N4/Bi2WO6 photocatalyst was synthesized by one-pot hydrothermal method.
Obviously, this thesis would provide promising strategies (green, sustainable, simple operation, and cost-effective) for the preparation of advanced heterogeneous photocatalytic systems with various structures, without using highly equipped laboratories. Besides, this study would provide highly efficient and stable photocatalytic systems for H2-fuel generation and
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water treatment. It is expected that these novel materials would be used for various applications in the near future. Chapter 2 “literature review” focuses on the literature review of heterogeneous photocatalysis, including UV-light-responsive (UVLR), visible-light-responsive (VLR), and VLR Z-scheme-based photocatalytic systems used to stand up to the energy and water problems. Recently, heterogeneous photocatalysis has been attracted much attention because of its efficient activity to provide a solution to the world energy crisis and the problems of environmental pollution. However, the photocatalytic activity of titania (the most broadly used) is limited by the rapid electron-hole recombination (causing low quantum yields of photocatalytic reactions). Moreover, TiO2 must be excited with UV irradiation (absorption edge at ca. ≤ 400 nm; depending on the polymorphic form and the content of defects and/or impurities), and thus only a slight part of solar radiation (ca. 2%) might be efficiently used for photocatalytic reactions. Therefore, various strategies have been proposed to improve the photocatalytic activity of titania. Among them, the formation of mixed-phase TiO2 could inhibit the charge carriers’ recombination, and non-metal doping could improve the separation efficiency of the charge carriers, and hence extending the light-harvesting ability to the visible light region. Therefore, great attention has been paid to fabricating the binary-phase (A/B) TiO2 photocatalyst because it exhibited an enhanced photocatalytic activity, compared with single-phase titania (A and B). Moreover, the C, N, and S tri-doping into the TiO2 lattice structure played an important role to modify the electronic structure of TiO2 catalyst, resulting in introducing new sublevels between the CB and VB, and thereby narrowing the band gap of titania to be activated by vis irradiation. In addition, the non-metal doping could also enhance the efficiency of charge carriers’ separation.