A two-step hydrothermal method was applied to synthesis Vanadium Sulfide (IV) coupled with commercial P25 on TiO2 nanoparticle (VS4-on-P25). Materials were characterized by scanning electron microscope (SEM), high-resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD), ultraviolet–visible spectroscopy (UV-Vis), diffuse reflectance UV-Vis spectroscopy and Raman spectroscopy. Photocatalytic activity of this new material was determined by photo-degradation of Methylene blue (MB) under UV irradiation. Experiments show that the VS4-on-P25 exhibits a higher photocatalytic activity than commercial P25 by providing more active site for dye adsorption, and reducing the recombination of charge carriers. Furthermore, the VS4-on-P25 extends its light-absorption spectrum into visible-light range due to its narrower band gap. The highest photocatalytic activity was found with a VS4 loading of 6 wt.%, which outperforms pure P25 by a factor of 2.29 in MB degradation rate.

The current Li-ion technologies allow the popularity of Li-ion batteries as electrical energy storage for both mobile and stationary applications. The graphite-based anode is most commonly used in commercial Li-ion batteries. However, because lithium intercalation in graphite occurs very close to the redox potential of Li/Li+, accidental lithium plating is a known hazard capable of resulting in internal shorting, particularly when the battery is charged rapidly, requiring higher overpotentials to accomplish the Li-intercalation. Moreover, toward the next-generation battery, a growing interest is now on promising rechargeable Na-ion batteries. The main motivation for Na-ion alternative is that sodium is much more abundant and widely distributed on the earth’s crust than lithium. In the first part of this dissertation, we investigate safer, higher specific capacity anode materials for both Li-ion and Na-ion batteries. In a separated effort toward the efficient solar energy harvesting, the second part of the dissertation examines thin film photoanodes, active in the visible-light region, for photoelectrochemical water oxidation. This part also discusses in detail the synthesis, characterization, as well as the use of co-catalysts to improve the electrode’s photochemistry performance. The current Li-ion technologies allow the popularity of Li-ion batteries as electrical energy storage for both mobile and stationary applications. The graphite-based anode is most commonly used in commercial Li-ion batteries. However, because lithium intercalation in graphite occurs very close to the redox potential of Li/Li+, accidental lithium plating is a known hazard capable of resulting in internal shorting, particularly when the battery is charged rapidly, requiring higher overpotentials to accomplish the Li-intercalation. Moreover, toward the next-generation battery, a growing interest is now on promising rechargeable Na-ion batteries. The main motivation for Na-ion alternative is that sodium is much more abundant and widely distributed on the earth’s crust than lithium. In the first part of this dissertation, we investigate safer, higher specific capacity anode materials for both Li-ion and Na-ion batteries. In a separated effort toward the efficient solar energy harvesting, the second part of the dissertation examines thin film photoanodes, active in the visible-light region, for photoelectrochemical water oxidation. This part also discusses in detail the synthesis, characterization, as well as the use of co-catalysts to improve the electrode’s photochemistry performance.

Photocatalytic water splitting using solar irradiation has the potential to produce sustainable hydrogen fuel on a large scale. Practical solar energy conversion requires the development of new, stable photocatalysts that operate efficiently under a broad range of visible wavelengths. Organic semiconductors are increasingly being employed as photocatalysts due to their earth abundance, aqueous stability, and optical absorptions that can be tuned to the solar spectrum. However, much remains unknown about the mechanism of organic semiconductor photocatalysis, and significant efficiency improvements need to be made before organic photocatalysts can achieve practical solar energy conversion. In chapter 2 the effect of residual Pd on hydrogen evolution activity in conjugated polymer photocatalysts was systematically investigated using colloidal poly(9,9- dioctylfluorene-alt-benzothiadiazole) (F8BT) nanoparticles (NPs). Residual Pd, originating from the synthesis of F8BT via Pd catalysed polycondensation polymerisation, was observed in the form of homogenously distributed Pd NPs within the polymer. Residual Pd was essential for any hydrogen evolution to be observed from this polymer, and very low Pd concentrations (<40 ppm) were sufficient to have a significant effect on the hydrogen evolution reaction (HER) rate. The HER rate increased linearly with increasing Pd concentration from <1 ppm to approximately 100 ppm, at which point the rate began to saturate. Transient absorption spectroscopy experiments support these conclusions and suggest that residual Pd mediates electron transfer from the F8BT NPs to protons in the aqueous phase. Photocatalysts formed from a single organic semiconductor typically suffer from inefficient intrinsic charge generation, which leads to low photocatalytic activities. In chapter 3 we demonstrate that incorporating a heterojunction between a donor polymer and non-fullerene acceptor in organic NPs can result in hydrogen evolution photocatalysts with greatly enhanced photocatalytic activity. Control of the nanomorphology of these NPs was achieved by varying the stabilizing surfactant employed during NP fabrication, converting it from a core-shell structure to an intermixed donor/acceptor blend, and increasing H2 evolution by an order of magnitude. The resulting photocatalysts display an unprecedentedly high H2 evolution rate of over 60,000 µmolh-1g -1 under 350 to 800 nm illumination and external quantum efficiencies over 6% in the region of maximum solar photon flux.

No description available.

Unavailable / Thesis (Master, Chemical Engineering) -- Queen's University, 2013-08-02 23:11:16.825

Les photocatalyseurs à base de TiO2 ont été l’objet d’une grande attention comme une méthode durable de purification de l’air ou de l’eau, et de production d’hydrogène par décomposition de l’eau. Une stratégie avantageuse consiste à développer des héterostructures par couplage avec un autre oxyde métallique former une jonction de type Schottky ou avec un autre oxyde métallique pour créer une jonction p-n à l’interface de manière à prévenir les recombinaisons via une séparation de charge « vectorielle » à ces jonctions. De plus, les facettes cristallines jouent un rôle crucial dans le piégeage des porteurs de charge et, donc,dans les réactions rédox photoactivées. Ainsi, le dépôt sélectif de métal ou d’oxyde métallique sur des facettes spécifiques de nanocristaux de TiO2 devrait augmenter l’activité photocatalytique par l’amélioration de la séparation des charges. Dans ce travail, nous avons combiné l’emploi du cocatalyseur de type p NiO pour former des jonctions p-n avec son dépôt sélectif sur des nanocristaux de TiO2 anatase exposant des facettes bien définies. Par ailleurs, des expériences modèles de physique de surface ont été menées pour étudier les propriétés électroniques de ces hétérojonctions. / TiO2 photocatalysts have attracted attention as a sustainable method for water/air purification and hydrogen production by water splitting. An advantageous strategy is the development of heterostructures by coupling metal oxides to create a p-n junction at their interface in order to prevent there combination by vectorial charge carrier separation at these energy junctions. In addition, crystal facets play a decisive role in the trapping of charge carriers and thus photocatalytic redox reactions. Thus, selective deposition of metal or metal oxides onto specific facets would enhance the photocatalytic activity by improving charge separation. In this work, we have combined the usage of p-type NiO co-catalyst to form p-n junction with its selective deposition onto the specific facet of oriented TiO2nanocrystal photocatalysts. Furthermore, the physical model experiments have been performed to investigate the electronic properties of these heterojunctions.

Liquid Phase Deposited (LPD) TiO2 film technology and the characterization of films were described in detail in this thesis. The LPD-TiO2 film can be utilized in electrochromic, photocatalyst and gas sensor devices. The optimum parameters for deposition of LPD-TiO2 were studied. First of all, we study the deposition properties and deposition parameter of LPD-TiO2 film. The effect of heating treatment on LPD-TiO2 film was investigated in this thesis. The as-deposited LPD-TiO2 film is amorphous and the TiO2 anatase phase can be obtained by annealing at 400 ¢J. The rutile phase can be observed at the annealing temperature of 900 ¢J. After annealing, the crystalling characteristic of LPD-TiO2 film can be improved and its refractive index can reach 2.46 annealed in O2 ambience. Its dielectric constant can be as high as 17 at annealing temperature of 700 ¢J in O2 ambience. LPD-TiO2 film can deposit on GaAs substrate successfully. The GaAs was etched by the treatment solution during deposition. Therefore, Ga and As are contained in the LPD film. The C-V characterization can be improved at annealing 400 ¢J. But the leakage current increases with higher annealing temperature. The electrochromic (EC) phenomena of TiO2 have been first reported by Inoue et al., where the films are prepared by hydrolysis of titanium tetraoxide. The film shows cathodic coloration and turns dark blue. The LPD-TiO2 film was deposited at 40 ¢J with (NH4)2TiF6 in the process of 0.1 M and 0.2 M boric acid. The films were transparent in the visible range and can be colored in a 1M LiClO4 + propylene carbonate solution. The deposition rate can be controlled quite well at 43 nm/hours. The 270 nm thickness LPD-TiO2 film gives the best electrochromic characteristic. In order to further strength the feasibility and enlarge the application of LPD-TiO2 film. The characterizations of Nb, Au and Pt doped LPD-TiO2 film were investigated. The concentrations of Nb and Au in the film can be controlled by adjusting the concentrations of Nb and Au source solution added into the treatment solution, respectively. The Nb, Au and Pt species in the LPD-TiO2 film are Nb2O5, metallic Au and Pt(OH)x, respectively. The crystallite size of metal-doped LPD-TiO2 film is smaller than that of pure LPD-TiO2 film. The photocalytic activities of undoped and Nb-doped LPD-TiO2 film were investigated. The photocatalytic activity of Nb-doped LPD-TiO2 film is about four times higher than that of pure LPD-TiO2 film. The gas sensing properties of undoped and Nb, Au and Pt-doped LPD-TiO2 films were investigated for oxygen detection sensitivity. Experimental results show that the Nb-doped LPD-TiO2 film displays the highest in oxygen detection, and the Nb-doped LPD-TiO2 film has also a shorter response time.

This thesis presents the synthesis and characterization of copper oxide nano photocatalyst for wastewater purification using visible light. The presented copper oxide nano material can serve as a low-cost and green technology for environmental applications. Uniform cubic, octahedral and rhombic dodecahedral Cu2O nano crystals with a size of 300-600 nm were synthesized using a simple hydrothermal method. The rhombic dodecahedral Cu2O nano crystals are highly active when driven by low-power white LEDs as a light source. In comparison with other reported photocatalysts, the Cu2O nano crystals in this work show a much higher reaction rate and lower electrical energy per order. The reaction rate and photoefficiency are found to be highly correlated with the irradiated photon flux. The surface termination and facet orientation of Cu2O nano particles were accurately tuned by adjusting the amount of hydroxylamine hydrochloride and surfactant. It is found that Cu2O nano particles with Cu-terminated (110) or (111) surfaces show high photocatalytic activity, while other exposed facets show poor reactivity. The density functional theory simulations confirm that the sodium dodecyl sulfate surfactant can lower the surface free energy of Cu-terminated surfaces, increasing the density of exposed Cu atoms at the surfaces, and thus benefiting the photocatalytic activity. It also shows that the poor reactivity of Cu-terminated Cu2O (100) surface is due to the high energy barrier of holes at the surface region. Amorphous CuxO nano flakes with a thickness of 10 to 50 nm were prepared through the dye-assisted transformation of rhombic dodecahedral Cu2O nano crystals under facile hydrothermal condition. The amorphous CuxO nano flake consists of a combination of Cu(I) and Cu(II) with a ratio close to 1:1. It shows enhanced photocatalytic reactivity towards the degradation of methyl orange compared to rhombic dodecahedral Cu2O nano crystals with all active (110):Cu facets. The chemical composition and architecture remain the same after repeating degradation tests. The high surface-to-volume ratio contributes to its better photocatalytic performance while its low surface energy calculated by the density functional theory simulations explains its improved stability. The as-obtained photocatalysts are able to degrade a wide range of aromatic organics including toluene, chlorobenzene and nitrobenzene effectively. We also demonstrate the capability of decontaminating a wide range of aromatic organics in industrial wastewater that comes from an oil company.

With an increasing demand for alternative clean energy solutions, much effort is being invested in the progression of nanoscale semiconductor materials in hopes of better harnessing solar energy. ZnO and TiO2 remain the most prominent photocatalytically active materials. This thesis reports on a comparison between nanoscale core-shell and hierarchical Zn-Ti-O/ZnO heterostructures. After a seed layer thickness optimization, hydrothermally grown ZnO nanorods were coated with mixed concentrations of Ti and Zn within an oxygen rich sputtering environment at two distinct temperature zones. Core-shell structures resulted from low temperature (23°C) depositions while hierarchical branch structures grew at high temperature (800°C). Excluding deposition temperature and the strategic variation of Zn and Ti gun power, every fabrication process remained identical between the two resultant heterostructure groups. Amongst the variety of samples produced, one from each heterostructure group proved notably similar in structural dimension, composition, and crystallization, yet demonstrated distinct differences in photoluminescence and dye degradation via UV-visible light spectroscopy. While photoluminescence results indicated core-shell heterostructure more photocatalytically promising, hierarchical heterostructure prevailed as the more powerful photocatalyst. Increased surface area due to hierarchical branching in conjunction with enhanced light exposure was believed responsible for the improved photocatalytic effectiveness.

The control of environmental pollution, particularly in wastewater treatment, is one of the major concerns of the 21st century. Among the currently available pollution control technologies, photocatalysis is one of the most promising and efficient approaches to the reduction of pollutants. Graphene, a carbon nanomaterial with specific physical and chemical properties, has been reported as a promising potential new catalyst material in this field. A Bi2WO6 photocatalyst modified with graphene oxide was synthesized in a two-step hydrothermal process. Compared with pure Bi2WO6, the modified photocatalyst with 1.2 wt% graphene oxide improved photoactivity during the degradation of rhodamine-B (RhB) dye pollutant, by facilitating the dissociation of photogenerated excitons, which in turn results in more O2- radicals. XRD characterization showed that the modification of Bi2WO6 with graphene oxide does not affect its structure or morphology. The adsorption properties of graphene also contribute to the improvement of photoactivity. Other parameters such as catalyst dosage, temperature and solution pH are studied, with the aim to improve the efficiency of RhB removal.