In our earlier work, silica-based diatom frustules were successfully converted to 3-dimesional F-doped titania-based replicas via shape-preserving gas/solid displacement reactions, and experiments showed that the hydrolysis of organophosphorous ester pesticides, methyl paraoxon (MOX) and methyl parathion (MTH) was significantly faster in the presence of these 3-D titania nanostructures than in the presence of other commercial titania nanoparticles. The enhancement effect of titania frustules appeared to be strongly related to the amount of F-doping on these materials. In this work, a wider range of titania frustule replicas with various F-doping were prepared and characterized, and compared in the hydrolysis of MOX and MTH as well as three carboxylic acids (methyl salicylate, methyl benzoate and methyl 4-(aminomethyl)benzoate). A strong relationship between the amount of F-doping and the enhancement effect on the hydrolysis of organophosphorous esters was still observed. However, such enhancement effect did not occur in the hydrolysis of the carboxylic acids. It was discovered that fluorine-leaching from the titania frustules was significant and yielded high concentration of fluoride ions in the reaction solutions. Dissolved fluoride ions alone could significantly catalyze the hydrolysis of organophosphorous esters but not that of carboxylic acids in the oxide-free systems. It is believed that fluoride ions act as nucleophilic catalysts to accelerate the hydrolysis of organophosphorous esters. Comparison in the hydrolysis product formation from the two potential hydrolysis pathways (i.e., the P-O bond and the C-O bond cleavages) in the studied systems also supports the direct involvement of dissolved fluoride ions in the observed catalytic effect.

TiO2 in anatase form is the most widely studied material for photocatalytic reactions. Utilization of oxide support materials such as silica with suitable transparency within band gap range of TiO2 is promising technique to obtain efficient photocatalysts for many applications. In the present study, simultaneous co-hydrolyzation of tetraethyl orthosilacate (TEOS) and titanium tetrabutaoxide (TBOT) precursors were carried out in the presence of hydrochloric acid. The effects of washing with low vapor pressure solvent(n-octane), drying conditions, hydrothermal ageing and TiO2/SiO2 ratio on the catalyst structure and photocatalytic activity were studied. The samples were characterized by XRD, BET, DRIFTS techniques and the activity was measured for liquid phase room temperature oxy/demineralization of phenol under artificial solar irradiation. The reaction intermediates were followed by UV/vis spectrophotometer and HPLC. It was found that the hydrothermal treatment contributes better degree of crystalinity, higher surface area and thus photocatalytic activity compared to the samples which were synthesized with conventional drying at 100oC overnight. The formation of Ti-O-Si interface indicating the degree of dispersion was evidenced by DRIFTS technique for all hydrothermally tretated samples. The highest surface area and photocatlytic activity was observed with hydrothermally treated catalyst with TiO2/SiO2:0.34 composition.

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Template synthesis and mesostructural characterization of ordered mesoporous silica, titania and carbon materials have been systematically investigated in this study. In order to obtain a better understanding of the template-precursor relationship, there are two templates adopted in this research. One is the ¡§liquid crystal template (LCT)¡¨, composed of surfactants via self-assembly pathway; the other is the ¡§ordered silica spheres template¡¨, composed of monodispersed SiO2 spheres (~40 nm) via gravity sedimentation. This work was carried out in four related directions: (1) Synthesis and functionalization of ordered mesoporous silicate (MCM-41 and MCM-48) via cationic surfactant template; (2) Using anionic surfactant template-assisted via urea treatment to control the morphology of the TiO2; (3) Synthesis of ordered mesoporous anatase TiO2 via cationic surfactant template; (4) Synthesis of ordered mesoporous carbon from mesophase pitch solution via silica spheres template. Mesoporous silica materials MCM-41 and MCM-48 have been synthesized and identified. The MCM-41 has a hexagonal phase (p6m) with surface area of 1006.90 m2/g and pore size of 37.65 Å, The MCM-48 has cubic phase ( ) with surface area of 1093.34 m2/g and pore size of 29.20 Å. The calcined MCM-41was rehydrated by heating in water and functionalized with 3-amino propyltrimethoxysilane; this functionalized mesoporous silica is targeted as a template of metal oxides, such as TiO2. appears the same tendency of parent MCM-41 in the N2 sorption isotherm measurements. Nanocrystalline TiO2 rods and hollow-tubes with an engraved pattern on the surface have been prepared by the anionic template-assisted sol-gel synthesis via urea treatment and under hydrothermal condition. X-ray diffractometry (XRD) results indicate that these nanocrystallines consist predominantly of anatase TiO2, with minor amounts of rutile and brookite. The crystallographic facetting found from SEM and TEM further reveals the polymorphic nature of the nanocrystalline TiO2 thus prepared. A ¡§reverse micelle¡¨ formation mechanism taking into account the hydrothermal temperature, the pH effect of the sol-gel system, the isoelectric point, the formation of micelles, and the electrostatic interaction between the anionic surfactant and the growing TiO2 particulates is proposed to illustrate the competition between the physical micelle assembly of the ionic surfactants and the chemical hydrolysis and condensation reactions of the Ti precursors. Ordered mesoporous TiO2 materials with an anatase framework have been synthesized by using a cationic surfactant template and soluble peroxytitanates as Ti precursor through an S+I− self-assembly pathway. The low-angle X-ray diffraction (XRD) pattern of the as-prepared mesoporous TiO2 materials indicates a hexagonal mesostructure. XRD and TEM results and N2 sorption isotherms measurements indicate the calcined mesoporous TiO2 possesses an anatase crystalline framework having a maximum pore size of 6.9 nm and a maximum BET specific surface area of 284 m2/g. This ordered mesoporous TiO2 also demonstrates a high photocatalytic activity for degradation of methylene blue under ultraviolet irradiation. Under a lower carbonization temperature and with a mesophase pitch solution as the carbon precursor, ordered mesoporous carbon thick films with 35-nm pore size have been synthesized using SiO2 spheres as the template. The pore size of the mesoporous carbon thus fabricated was the smallest one ever reported using silica templates. SEM and TEM patterns show a discernible morphology of an ordered cubic close-packing of the mesopores interconnected via holes of 6 nm in diameter. From this study, the template synthesis has been proven to be an effective method to fabricate mesoporous silica, polymorphic titania, ordered mesoporous TiO2, and ordered mesoporous carbon materials. Further utilization of this template synthesis is expected to offer a variety of porous networks with a wide range of pore sizes, well-defined morphologies on controllable length scales, and various chemical functionalities to match the needs of different applications.

Membrane materials for gas separations span a wide range including polymers, metals, ceramics and composites. Our aim is to create economical hydrothermally stable membranes that can provide high H₂-CO₂ separation at a temperature of 300 degree Celsius, for application in the water-gas shift reactor process. The present work describes the development of novel silica and silica-titania membranes from the controlled oxidative thermolysis of polydimethylsiloxane. The scope of this thesis is fabrication of membranes, material characterization and preliminary gas permeation tests (35-80 degree Celsius) on PDMS derived silica membrane films. The developed membranes can withstand up to 350 degree C in air. High permeabilties of small gas penetrants like He, H₂ and CO₂ have been observed and fairly high separation factors of O₂/N₂=3, H₂/N₂= 14 and H₂/CH₄=11 have been obtained. As the temperature of operation increases, the permeability of hydrogen increases and the separation factor of H₂ from CO₂ increases. The silica membranes exhibit gas separation factors higher than the respective Knudsen values. Additionally, design and construction of a new high temperature gas permeation testing system is described, which will cater to gas permeation tests at temperatures up to 300 degree Celsius for future work. The thesis also includes a detailed plan for future studies on this topic of research.

Flame-based synthesis is an attractive industrial process for the large scale generation of nanoparticles. In this aerosol process, a gasifi ed precursor is injected into a high-temperature turbulent flame, where oxidation followed by particle nucleation and other solid phase dynamics create nanoparticles. Precursor oxidation, which ultimately leads to nucleation, is strongly influenced by the turbulent flame dynamics. Here, direct numerical simulation (DNS) of a canonical homogeneous flow is used to understand the interaction between a methane/air flame and titanium tetrachloride oxidation to titania. Detailed chemical kinetics is used to describe the combustion and precursor oxidation processes. Results show that the initial precursor decomposition is heavily influenced by the gas phase temperature field. However, temperature insensitivity of subsequent reactions in the precursor oxidation pathway slow down conversion to the titania. Consequently, titania formation occurs at much longer time scales compared to that of hydrocarbon oxidation. Further, only a fraction of the precursor is converted to titania, and a signi cant amount of partially-oxidized precursor species are formed. Introducing the precursor in the oxidizer stream as opposed to the fuel stream has only a minimal impact on the oxidation dynamics. In order to understand modeling issues, the DNS results are compared with the laminar flamelet model. It is shown that the flamelet assumption qualitatively reproduces the oxidation structure. Further, reduced oxygen concentration in the near-flame location critically a ffects titania formation. The DNS results also show that titania forms on the lean and rich sides of the flame. A reaction path analysis (RPA) is conducted. The results illustrate the di ffering reaction pathways of the detailed chemical mechanism depending on the composition of the mixture. The RPA results corroborate with the DNS results that titania formation is maximized at two mixture fraction values, one on the lean side of the flame, and one on the rich side. / text

Steady state reflectance and emission characteristics of anthracene adsorbed on silica gel and titania-silica mixed oxides have been investigated as a function of sample loading. Titania-silica mixed oxides with 1, 3, 5 and 10 wt. % TiO2 were prepared by two different methods: a dropwise method and a sol-gel route. Ground state diffuse reflectance and fluorescence emission spectra of anthracene adsorbed on titania-silica surfaces show a dependence on titania content. The absorption peaks of anthracene are difficult to resolve at higher titania content due to the increasing red-shift of the titania absorption edge. The absorption edge of titania is shifted to longer wavelengths and the band gap energy decreases with increasing the titania loading. Diffuse reflectance laser flash photolysis at 355 nm produces both the triplet and radical cation of anthracene and gives relevant information regarding the photochemical transients and the kinetics details of the surface photochemical processes. Energy dependence studies confirm the monophotonic nature of the triplet production, whereas the anthracene radical cation is formed by monophoton or multiphoton ionisation in the mixed titania-silica systems. Energy and electron transfer reactions of anthracene co-adsorbed with azulene as electron donor on silica sol-gel and titania-silica mixed oxides prepared by the sol-gel method with different titania content have been studied using the time-resolved diffuse reflectance laser flash photolysis technique. The fluorescence of excited anthracene adsorbed on silica sol-gel is quenched by the addition of azulene, while co-adsorption of azulene on titania-silica mixed oxides resulted in a decrease in the fluorescence intensity of the adsorbed anthracene due to the formation, at the same time, of anthracene radical cation and Ti3+ species on the titania-silica surface. Triplet-triplet energy transfer from the excited anthracene to ground state azulene and electron transfer from azulene to the anthracene radical cation have been investigated using a time-resolved diffuse reflectance laser flash photolysis technique following laser excitation at 355 nm. Bimolecular rate constants for energy and electron transfer between anthracene and azulene have been obtained. Kinetic analysis of the decay of the anthracene triplet state and radical cation show that the kinetic parameters depend on the titania content of the sample and the azulene concentration. This indicates that the rate of energy and electron transfer reactions increases as a function of azulene concentration and decreases with increasing titania content in titania-silica mixed oxides, whereas the observed rate of reaction on silica sol-gel is predominantly governed by the rate of diffusion of azulene. Electron transfer reactions in a ternary system using azulene for hole transfer between 9-anthracenecarboxylic acid radical cation as electron acceptor and perylene as electron donor were also studied in order to demonstrate the mobility of radical cations on the silica sol-gel and titania-silica surfaces. The co-adsorption of azulene as a molecule shuttle with 9-anthracenecarboxylic acid and perylene on both silica sol-gel and titania-silica systems has been shown to enhance the rate of electron transfer in this ternary system. Activation energies for energy and electron transfer on photoinduced bimolecular and termolecular processes on silica sol-gel and titania-silica mixed oxides have been measured. In bimolecular anthracene / azulene systems, at higher azulene loadings, the activation energies and the pre-exponential factors on titania-silica surfaces are the same for both energy and electron transfer and are comparable with the parameters extracted for azulene diffusion on silica Davisil suggesting that azulene diffuses across the silica Davisil and titania-silica mixed oxides surfaces, while at lower azulene loadings, ion-electron recombination dominates and the activation energy extracted is for this process. In a ternary 9-anthracenecarboxylic acid / azulene / perylene system, the activation energy for perylene diffusion is higher than that observed for the anthracene / azulene system, reflecting the lower mobility of the perylene molecule. In this study, a series of titania-silica samples with different loadings of titania (1 10 wt. %) prepared by the sol-gel method and also the pure TiO2 P25 Degussa have been used to study the photocatalytic degradation of 4-chlorophenol in aqueous solution under UV light irradiation. The absorption peak of 4-chlorophenol at 280 nm decreases with increasing titania content and finally disappeared suggesting that titania has a positive influence on the degradation of 4-chlorophenol. The investigated titania-silica mixed oxides prepared by the sol-gel method are less efficient photocatalysts for the degradation of 4-chlorophenol than TiO2 P25.

This work addresses fundamental aspects of designing templates and curing conditions for the synthesis of mesoporous metal oxide thin films. The first section addresses selection of cationic-carbohydrate surfactant mixtures to synthesize templated silica thin films for selective adsorption of simple carbohydrates based on molecular imprinting. Nuclear magnetic resonance and fluorescence spectroscopy results suggest a novel structure for mixtures of alkyl glucopyranosides or xylopyranosides with cationic (trimethylammonium) surfactants. Despite thermodynamically favorable mixing, the carbohydrate headgroups in the mixed micelle adopt an inverted configuration with their headgroups in the micelle core, and therefore are inaccessible for molecular imprinting. This orientation occurs even when the alkyl tail length of the carbohydrate surfactant is greater than that of the cationic surfactant, but this limitation can be overcome by introducing a triazole linker to the carbohydrate surfactant. The next section addresses the effects of aging conditions on the structural and chemical evolution of surfactant templated silica thin films. The third section describes the synthesis of carbohydrate/cationic surfactant imprinted silica thin films with orthogonally oriented cylindrical pores by modifying the glass surface with a random copolymer. The last part of the dissertation addresses the effect of pore orientation on the transformation mechanism of block copolymer templated titania thin films during high temperature curing. Mesoporous titania thin films can be used for photochemical and solar cell applications, but doing so requires addressing the tradeoff between loss of mesostructural order and growth of crystallinity during thermal treatment. By using advanced x-ray scattering techniques it has been shown that the titania films with vertically oriented pores can better withstand the anisotropic stress that develops during thermal treatment compare to titania films with mixed pore orientation. For instance, films with parallel or mixed pores can only be heated at 400 °C for a brief time (~10 min) without loss of order, while orthogonally oriented films can be heated at 550 °C or greater for extended time periods (on the order of hours) without significant loss of long-range mesopore structure. Detailed kinetic modeling was applied to enable the comparison of activation energy for mesostructure loss in films as a function of pore orientation and thickness.

A study on Prince Edward Island was initiated to assess the impact of organic fertility amendment rate and timing treatments and deflowering on the growth, yield, and berry size and soluble solids, and plant and soil available nutrients of blackcurrants (Ribes nigrum L cv. Titania.). Plants at the site with lower leaf P and K showed lower growth and yield (492-2540 kg ha-1) than the other site (3935-5016 kg ha-1No significant differences were found in final size or 2011 yield at the site with larger bushes, while at the other site the medium spring fertility treatment gave the greatest growth and yield, followed by the high spring fertility treatment. Deflowering increased yield but not growth at the site with recommended ranges of leaf P and K; at the site with P and K deficiencies, growth increased in 2010 and 2011. There was no interaction between deflowering and amendment timing.

Increasing energy demands as well as the depletion of traditional energy sources has led to the need for the development and improvement of energy conversion and storage technologies. Concerns regarding climate change and environmental awareness has also created increased support for renewable energy and clean technology research. One technology of interest is the photocatalyst, which is a material that is able to use natural light irradiation to create electrical currents or drive useful chemical reactions. For this purpose, a strong photocatalytic material has the following properties: i) strong absorbance over a wide solar radiation spectrum; ii) high surface area for adsorbance of target species; iii) high electron efficiency characteristics such as high conductivity, long charge-carrier lifetimes, and direct pathways for electron transport; and iv) good chemical stability. All of these requirements serve to maximize the efficiency and overall output of the device, and are a means of overcoming the performance hurdle required for the commercialization of various energy conversion technologies. Unfortunately, current photocatalytic materials suffer from small absorbance windows and high recombination rates which greatly reduce the conversion efficiency of the catalyst. Titanium dioxide (TiO2), the most well-known and widely used photocatalyst, can only absorb light within the ultraviolet (UV) range – which accounts for only a small fraction of the entire solar spectrum. For this reason, the majority of recent research has been directed toward producing photocatalysts that are able to absorb light within the visible and infrared range in order to maximize the amount of light absorbed in the solar spectrum. Other research is also being conducted to increase electrical conductivity and charge-carrier separation to further increase conversion efficiency. It is hoped that these two major problems surrounding photocatalysis can be solved by using novel functional nanomaterials. Nanomaterials can be synthesized using three main techniques: crystal structuring, doping, and heterostructuring. By controlling the structure of the crystal, materials of different phase, morphology, and exposed crystal facets can be synthesized. These are important for controlling the electronic properties and surface reactivity of the photocatalyst. Doping is the act of introducing impurities into a material in order to modify its band structure and create a red shift in light absorption. Lastly, heterostructuring is a method used to combine different photocatalysts or introduce co-catalysts in order to widen the range of absorption, encourage charge separation, or both. Many novel photocatalytic materials have been synthesized using these techniques. However, the next-generation photocatalytic material has remained elusive due to the high cost of production and complexity of synthesis. This thesis proposes a novel photocatalytic material that can be used in photocatalyzed waste-water remediation. Graphene-wrapped hierarchical TiO2 nanoflowers (G-TiO2) are synthesized using a facile synthesis method. TiO2 is a material of particular interest due to its chemical and photo-corrosion stability, high redox potential, strong electronic properties, and relative non-toxicity. Hierarchical structures are highly desired because they are able to achieve both high surface area and high conductivities. Graphene hybridization is a popular method for creating composites with highly conductive networks and highly adsorptive surfaces. To the best of my knowledge, the hybridization of graphene on hierarchical TiO2 structures without pre-functionalization of TiO2 has not yet been demonstrated in literature. Therefore, it is proposed that the use of such a material would greatly simplify the synthesis process and enhance the overall photocatalytic performance of TiO2 over that of commercial TiO2 photocatalysts. In the first study, hierarchical TiO2 nanoflowers are synthesized using a solvothermal reaction. It is then shown that under UV irradiation, the hierarchical TiO2 material is able to outperform commercial TiO2 material in the photodegradation of methylene blue (MB). Further characterization shows that this improvement is explained by a higher electrical conductivity, and exists in spite of having a lower specific surface area compared to the commercial material. In the second study, G-TiO2 is synthesized by mixing hierarchical TiO2 nanoflowers with graphene oxide (GO) and reducing GO in a hydrothermal reaction. Photocatalytic tests show that this hybridization further improves the performance of the hierarchical TiO2. Further studies reveal that an optimal graphene loading of 5 wt% is desired in order to achieve the higher rate of MB decomposition, and greatly outperforms P25 in this task. Characterization shows that G-TiO2 composites have increased specific surface area and electrical conductivity compared to the hierarchical TiO2 nanoflower. It is believed that this work will provide a simple and efficient avenue for synthesizing graphene–TiO2 composites with greatly improved photocatalytic activity. This work may also find use in other photocatalytic applications such as chemical deconstruction and manufacturing, hydrogen production, solar cells, and solar enhanced fuel cells.