Titanium dioxide is a well-studied and popular photocatalyst, but a number of factors still prevent its widespread use in a number of commercial applications. In this thesis we explored the synthesis of titanium dioxide nanoparticles via the sol-gel method, with the goal of creating a viable catalyst for the visible-light degradation of wastewater dyes. A number of different synthetic pathways were explored and developed, and the products categorised with respect to nanoparticle size, shape and crystallinity as well as electronic and photocatalytic properties.

Nanoparticles of MoS2 and WS2 were synthesized by decomposing the appropriate metal hexacarbonyl in the presence of sulfur dissolved in decalin at 140°C. A significant fraction of the nanoparticles was ≤ 15 nm in diameter as verified by Transmission Electron Microscopy. The process was repeated in the presence of silica and then titania to produce supported metal sulfides. The unsupported nanoparticles were found to exhibit a size-dependent shift in their threshold UV-visible absorption due to quantum confinement. Photocatalytic properties of each sulfide from synthesis in decalin were explored by using each as a catalyst in the photodegradation of methylene blue by visible light. These sulfides were also used to catalyze the photodegradation of acetone. Unsupported MoS2 and WS2 nanoparticles catalyzed the photodegradation of acetone under visible light of ≥ 400 nm wavelength. This is the first study reporting the photocatalytic properties of the unsupported WS2 nanoparticles. Photodegradation of methylene blue under ≥ 435 nm irradiation was detected using unsupported WS2 but not unsupported MoS2, likely because activity was masked by the likely photobleaching of the dye. When deposited on silica or titania, the nanosized MoS2 and WS2 could be uniformly distributed in aqueous solutions to maximize the photocatalytic efficiency. Correcting the absorbance measurements for light scattering by solids proved to be beneficial for extracting kinetic information. Both silica deposited sulfides were found to significantly increase the rate of methylene blue photodegradation, and deposited WS2 increased this rate significantly more than deposited MoS2. Similarly, both titania deposited sulfides significantly increased the rate of methylene blue photodegradation, and the deposited WS2 increased this rate significantly more than the deposited MoS2 / Synthesis of the sulfide photocatalysts -- Characterization of synthesized nanoparticles -- Photocatalytic degradation tests : setup and protocols -- Photocatalytic degradation tests : results. / Department of Chemistry

Semiconductor photocatalysis has received considerable attention in recent years as an alternative for treating water polluted with hazardous organic chemicals. The process, as a means of removal of persistent water contaminants such as pesticides, which exhibit chemical stability and resistance to biodegradation, has attracted the attention of many researchers. To a lesser extent, it has also been studied for decontamination of water containing toxic metals. Precious and common metals enter waters through washing, rinsing, pickling and surface treatment procedures of industrial processes, such as hydrometallurgy, plating and photography. As a result we are living in an environment with a multitude of potentially harmful toxic metal ions. In contrast, the demand for metals increases significantly with the development and growth of industry. Even though research on the photocatalytic recovery of waste and noble metals has escalated in the past 10 years, the practical implementation of these processes is not yet justified. The successful implementation of large scale reactors, for industrial application, has to consider several reactor design parameters that must be optimised, such as reactor geometry and the utilization of radiated energy. In this study the effect of various parameters such as initial platinum(IV)chloride concentrations, initial sacrificial reducing agent (ethanol) concentrations, catalyst (TiO2) concentration, pH, temperature and light intensity has been investigated as a first step towards optimising a photocatalytic batch and photocatalytic flow reactor. Langmuir–Hinshelwood kinetics has been applied to calculate the photocatalytic rate constant kr as well as the adsorption equilibrium constant Ke for both the initial platinum(IV) dependency as well as the initial ethanol concentration dependency. The results in this study may be used in future work for the optimisation and comparison of both batch and flow reactors towards the industrial implementation of these processes. / Thesis (M.Sc. (Chemistry))--North-West University, Potchefstroom Campus, 2012.

Semiconductor photocatalysis has received considerable attention in recent years as an alternative for treating water polluted with hazardous organic chemicals. The process, as a means of removal of persistent water contaminants such as pesticides, which exhibit chemical stability and resistance to biodegradation, has attracted the attention of many researchers. To a lesser extent, it has also been studied for decontamination of water containing toxic metals. Precious and common metals enter waters through washing, rinsing, pickling and surface treatment procedures of industrial processes, such as hydrometallurgy, plating and photography. As a result we are living in an environment with a multitude of potentially harmful toxic metal ions. In contrast, the demand for metals increases significantly with the development and growth of industry. Even though research on the photocatalytic recovery of waste and noble metals has escalated in the past 10 years, the practical implementation of these processes is not yet justified. The successful implementation of large scale reactors, for industrial application, has to consider several reactor design parameters that must be optimised, such as reactor geometry and the utilization of radiated energy. In this study the effect of various parameters such as initial platinum(IV)chloride concentrations, initial sacrificial reducing agent (ethanol) concentrations, catalyst (TiO2) concentration, pH, temperature and light intensity has been investigated as a first step towards optimising a photocatalytic batch and photocatalytic flow reactor. Langmuir–Hinshelwood kinetics has been applied to calculate the photocatalytic rate constant kr as well as the adsorption equilibrium constant Ke for both the initial platinum(IV) dependency as well as the initial ethanol concentration dependency. The results in this study may be used in future work for the optimisation and comparison of both batch and flow reactors towards the industrial implementation of these processes. / Thesis (M.Sc. (Chemistry))--North-West University, Potchefstroom Campus, 2012.

Pasaulyje neslopsta susidomėjimas fotokataliziniais procesais, kuriuos siekiama pritaikyti vandens skaidymo į vandenilį ir deguonį, organinių ar neorganinių junginių nukenksminimo technologijose. Fotoelektrocheminis vandens skaidymas į elementus vertinamas kaip vienas perspektyviausių būdų, galinčių ateityje užtikrinti efektyvų atsinaujinančių energijos šaltinių panaudojimą. Kuriant fotokatalizines sistemas, nanostruktūrinis titano dioksidas (TiO2) išlieka viena tinkamiausių ir labiausiai tyrinėtų medžiagų. Tačiau titano dioksidas neaktyvus regimosios spinduliuotės srityje, todėl alternatyva TiO2 fotokatalizatoriui gali būti kitas n-tipo puslaidininkis – volframo trioksidas (WO3). Volframo trioksidui yra būdingos fotochrominės savybės, jis absorbuoja dalį regimosios spinduliuotės. Daugelio tyrėjų nuomone, norint padidinti jo fotokatalizinį aktyvumą, tikslinga kurti mišrius oksidinius katalizatorius arba modifikuoti paviršių kitomis medžiagomis. Atsižvelgiant į literatūroje pateiktus duomenis, šiame darbe buvo siekiama pagaminti aktyvius kompozitinius fotokatalizatorius, kurių pagrindinė sudedamoji dalis yra volframo trioksidas. Darbas skirtas naujų medžiagų, kurios galėtų būti naudojamos fotokataliziniuose ir fotoelektrocheminiuose procesuose, paieškai ir charakterizavimui. Šio darbo tikslas – susintetinti TiO2, Se ir Co–P priedais modifikuotus volframo trioksido katalizatorius, ištirti jų struktūrą, fotokatalizines bei fotoelektrochemines savybes. / Scientific community exhibits a great interest in photocatalytic processes such as water photosplitting or photooxidation of organic substances. The photoelectrochemical splitting of water into hydrogen and oxygen is considered as the very promising pathway in the development of a long-term, sustainable energy economy. Titania (TiO2) still remains to be the most suitable for practical applications. However, using it as a photocatalyst still has some major issues: due to the fast recombination of photogenerated charge carriers, the overall quantum efficiency is relatively low, and titania is mostly sensitive to UV irradiation. Tungsten trioxide (WO3) is another semiconductor which can be employed in photocatalysis. Besides its photochromic properties, it has a smaller band gap than titania and may be activated under visible light illumination. In order to improve the photocatalytic efficiency it may be reasonable enough to combine both titania and tungsten trioxide into one photocatalyst or to modify their surface with various compounds. This work is relevant in the search of new materials suitable for photocatalytic and photoelectrocatalytic processes. The main object of this work was to synthesize active tungsten oxide-based composite catalysts and evaluate their structure and properties. Aim of the work was to synthesize WO3 catalysts modified with TiO2, Se and Co-P additives, to investigate their structure, photocatalytic and photoelectrochemical properties.

Natural organic matter (NOM) occurs ubiquitously in drinking water supplies and is problematic since it serves as a precursor to disinfection by-products (DBPs) formation. Stricter DBP regulations will drive utilities to consider advanced treatment processes for DBP control through NOM removal. Herein, the transformation of NOM in homogeneous (UVA/H2O2 and UVA/Fe/H2O2) and heterogeneous (UVA/TiO2) Advanced Oxidation Processes (AOPs) were studied. Organic matter from three different sources was investigated in this work, specifically a commercial humic acid, and two Australian surface water sources. The transformation of the organic matter as a result of oxidation was investigated through multiple analytical techniques, such as UV-Vis spectroscopy, DOC analysis, high performance size exclusion chromatography (HPSEC), resin fractionation, liquid chromatography with organic carbon detection (LC-OCD) and disinfection byproducts formation potential. The multi-analysis approach is required due to the complex and heterogeneous nature of NOM. Each analytical technique provides complementary information on different properties of NOM, leading to a comprehensive understanding on how AOPs transform the chemical and physical properties of NOM. Both homogeneous and heterogeneous AOPs were found to be effective for NOM removal. However, complete mineralisation was not achieved, even under prolonged irradiation. Large aromatic and hydrophobic organics were degraded into lower molecular weight hydrophilic compounds, which had weak UV absorbance at 254 nm. In the UVA/TiO2 treatment, multi-wavelength HPSEC analysis demonstrated the formation of low molecular weight compounds with strong absorbance at wavelength lower than 230 nm. These residual organic compounds, though recalcitrant, had a low reactivity to chlorine to form THMs, and were identified to be low molecular weight acids and neutral compounds from LC-OCD analysis. Finally, the current work reports the novel synthesis of magnetic photocatalyst for NOM oxidation from low cost precursors to solve the separation problem of nano-sized particles. Magnetite particles were coated with a layer of protective silica from sodium silicate precursor. Photoactive titanium dioxide was then deposited onto the silica coated particles using titanium tetrachloride precursor. The as-prepared magnetic photocatalyst exhibited excellent stability and durability. Although the photoactivity of the magnetic photocatalyst is lower than commercial TiO2 photocatalyst, it can be easily recovered by magnetic field.

This century has seen a phenomenal growth in energy demands and environmental pollution, which has given rise to a worldwide awareness for the need to address these issues immediately. / This thesis focuses on the fabrication of high performance electrocatalysts applied in fuel cells and developing appropriate advanced oxidation processes for environmental remediation. It has been shown that ultrasonic irradiation is a promising method of synthesizing nanometre sized metal colloids with specific properties. Sonophotocatalysis has proved to be an effective process for the degradation of organic pollutants / The synthesis of platinum monometallic and platinum-ruthenium bimetallic nanoparticles was successfully achieved by using sonochemical irradiation. A chemical method and a hybrid method were used to reveal and understand the process of Ru(III) reduction by sonochemistry. TEM images of the Pt and PtRu monometallic/bimetallic particles indicate typical diameters of less than 10 nm. An effort was made to investigate the influence of two different methods, namely simultaneous and sequential sonochemical reduction, on the structure and formation of PtRu bimetallic nanoparticles. It has been shown that the sequential reduction method produces a relatively higher yield of core-shell nanoparticles than the simultaneous reduction method. It has been concluded that Pt nanoparticles, which are formed first, play an important role in catalysing the formation of Ru nanoparticles. / A number of methods including chemical, sonochemical and radiolytic synthesis were used to fabricate platinum and platinum-ruthenium monometallic/bimetallic nanoparticles. Furthermore, the evaluation of the electrocatalytic performance of these particles was performed by using cyclic voltammetry. Simultaneous and sequential methods for the synthesis of PtRu were adopted to investigate their influence on the electrocatalytic performance of these bimetallic nanoparticles. thas been shown that simultaneous reduction is an effective means of fabricating high performance electrocatalytic PtRu catalysts. A number of experiments with different ratios of platinum to ruthenium ions in precursor solution were carried out to study the effect of the ruthenium composition in platinum-ruthenium electrodes. It has been found that the methanol oxidation ability of platinum-ruthenium bimetallic nanoparticles can change with the alternation of ratio of Pt(II) to Ru(III) in the precursor solution. Simultaneous radiolytic reduction has the potential to fabricate higher performance electrocatalytic bimetallic nanoparticles. / Although both photo-oxidation and sono-oxidation techniques are fascinating solutions to the environmental problems at hand, the critical limit of these individual processes is their low efficiency of environmental remediation. In my project, sonolysis and photocatalysis (sonophotocatalysis) have been simultaneously employed to degrade selective organic pollutants in aqueous environments, such as methyl orange, p-chlorobenzoic acid, p-aminobenzoic acid and p-hydroxybenzoic acid. Experiments have been carried out in order to improve the efficiency of sonophotocatalytic reactions to ensure that a substantial amount of the electrical energy is utilized in degrading the organic pollutants. / Methyl orange, an azo dye, was selected as the degradation target for sonophotocatalysis. An orthogonal array analysis method was employed to clarify the correlation between the efficiencies of sonolysis, photocatalysis and sonophotocatalysis and the various operation conditions studied. Emphasis was placed on investigating the influence of pH and the ultrasound parameters on these three advanced oxidation processes. It was of interest to find that the degradation of methyl orange originates from hydroxylation and demethylation processes preceding aromatic ring-opening. / Sonophotocatalysis was also applied in the degradation of three aromatic carboxylic acids, p-chlorobenzoic acid, p-hydroxybenzoic acid and p-aminobenzoic acid. Experiments were carried out in order to get a thorough understanding of the synergy effects produced by combining the two oxidation techniques. A number of advanced analytical techniques, such as HPLC and Q-TOF MS/LC, were employed to comprehensively monitor and analyse the sonophotocatalytic degradation process. It has been found that synergistic effects of the combined system have been identified with respect to the parent organic pollutant as well as its degradation products. Additionally, products were quantitatively analysed by a kinetic simulation method in order to understand the reaction mechanism. This method also allowed us to quantify the synergy effects. It was observed that the solution pH played a key role in determining the degradation rate and controlling the direction of the degradation reaction. Based on the analytical data gathered, the sonophotocatalytic degradation pathway of the aromatic carboxylic acids was established. The experimental results suggest that the sonophotocatalytic technique is likely to lead to a complete mineralization of organic pollutants in aqueous solutions.

No description available.

Thesis (Ph.D.)--University of Delaware, 2007. / Principal faculty advisor: S. Ismat Shah, Dept. of Materials Science . Includes bibliographical references.

Thesis (M.S.)--University of Wyoming, 2008. / Title from PDF title page (viewed on Mar. 26, 2010). Includes bibliographical references (p. 71-73).