This research program is focused on the photocatalytic cement with emphasis on evaluating impacts on concrete’s physical, transport and durability properties. The scope of this project is to examine three key aspects of photocatalytic concrete including: a critical review of currently reported applications; an examination of air pollution concentrations in Ontario to assess the potential effectiveness of photocatalytic concrete, with respect to NOx; and an experimental study to characterize the material properties. Research findings revealed comparability between photocatalytic concrete and conventional concrete in mechanical and fluid transport properties. Although photocatalytic concrete resisted rapid freeze and thaw damage very well, in terms of de-icer salt scaling performance, only formed surface performed well and highly variable results for photocatalytic and GU concrete was observed for the finished surface.

This research program is focused on the photocatalytic cement with emphasis on evaluating impacts on concrete’s physical, transport and durability properties. The scope of this project is to examine three key aspects of photocatalytic concrete including: a critical review of currently reported applications; an examination of air pollution concentrations in Ontario to assess the potential effectiveness of photocatalytic concrete, with respect to NOx; and an experimental study to characterize the material properties. Research findings revealed comparability between photocatalytic concrete and conventional concrete in mechanical and fluid transport properties. Although photocatalytic concrete resisted rapid freeze and thaw damage very well, in terms of de-icer salt scaling performance, only formed surface performed well and highly variable results for photocatalytic and GU concrete was observed for the finished surface.

The photocatalytic conversion of carbon dioxide (CO2) to methanol was investigated. The procedure for the carbon dioxide conversion was carried out using a small scale filter type photocatalytic reactor. In conducting the experiments, carbon dioxide mixed with water vapor was discharged into the photocatalytic reactor in the presence of a catalyst and light irradiation from a UV lamp for conversion to methanol. The catalyst that were used for the experiments were titanium dioxide (titania) and copper-loaded titania which were impregnated on a ceramic filter that was initially treated with gamma-alumina which was a good catalyst support for the catalyst. SEM, XRD and particle size analysis was performed as a means of characterization of the catalyst. The effect of the flow rate of carbon dioxide on the conversion process using a UV lamp with a wavelength of 254 nm was studied.

<p> Our work demonstrates the decomposition results obtained using Ti02 coated paper at different pH, ionic strength, UV intensities, temperature and flow rates. A kinetic model ofTi02 photocatalytic decomposition of reactive azo dye (RBS) was developed for the different conditions. </p> <p> Ti02 coated paper was developed by simply spraying Ti02 suspension on the filter paper. The stability of the Ti02 coated paper was studied and the environment where Ti02 coated paper can be used is under pH 7. The stability of Ti02 attached on the paper surface is determined by the property of the polymeric retention aids and the adsorption of reactive azo dye (RB5) is dependent on the electrostatic attraction. </p> <p> Ti02 photocatalytic decomposition mainly occurs at the surface of Ti02. So the adsorption of RBS molecules is considered to be one of the most important factors, which can affect the decomposition rate. Other factors, such as UV intensity and temperature, can also change the decomposition rate by affecting the formation of free radicals. </p> <p> New discovery of intermediate products can make the mechanism of the photocatalytic decomposition more clear, although the specific information about the intermediate products is not available yet. The adsorption and decomposition of intermediate products provide useful information for developing the decomposition kinetic model. </p> <p> Langmuir adsorption model is fit for the adsorption of RB5 and its degradation intermediate products at Ti02 surface. Our kinetics model combines the principles of Langmuir-Hinshelwood model and two-step first order model. It can describe the change of the RB5 concentration in the bulk and predict the desorption of intermediate products. </p> / Thesis / Master of Applied Science (MASc)

Photocatalytic membranes have been designed using two types of fine-scale alumina fibres, namely Nano Alumina Fibre (NAF) from Metallurg Engineering, Estonia and commercially available Saffil® Alumina Fibre (SAF) produced by Saffil Limited, UK. NAF fibres have an average diameter of about 15 nm and SAF about 4 μm. Membranes were produced in various ways. The fibre network architecture within the membranes, along with their porosity, specific surface area and mechanical properties, have been examined. These NAF-SAF membranes were impregnated with titania-based sol-gel coatings, to produce photocatalytic membranes. Their mechanical properties, specific surface area and flow properties were assessed and photocatalytic potential was measured by studying rates of degradation of aqueous dye solution. Membranes with photo-active top layers were designed by sedimentation of a fibrous layer of NAF-SAF, containing titania nanoparticles on a pre-sedimented support layer. Two types of photocatalyst were used, one a commercially available anatase nanopowder and the other silver-coated anatase. The latter was produced via modification of the first. Optimisation of the nanoparticle loadings was performed via assessing their photocatalytic efficiency. Specific permeability values were obtained experimentally and by prediction from the pore architecture. A novel form of photo-active membrane was designed by direct casting of milled SAF and titania-based sol-gel into circular moulds. Effects of fibre milling time and fibre to sol-gel ratio on their performance were studied, besides mechanical properties, porosity and specific surface area. Their flow properties and photocatalytic efficiency were also examined. Due to the availability of these fibres, especially the high production rates (kg/h range) and low cost of NAF, these membranes offer potential for large scale application.

In this study, the photocatalytic mineralization of the industrial dump-site leachate was evaluated using an internally-irradiated 18-Litre pilot-scale aerated annular bubble column photoreactor. The study includes evaluating the effect of catalyst loading, leachate initial concentration, initial solution pH, light intensity and oxygen partial pressure. The reaction runs were performed over a 48-hours period at room temperature and atmospheric pressure. Titanium catalyst loading was optimized to be 3 gL-1 where the reaction rate constant 20x10-6 mol L-1 min-1.Beyond this dosage, the effect of light scattering by the catalyst particles were noticed on dropping the degradation rate. Moreover, at high catalyst loading, particles aggregates reduce the interfacial area between the reaction solution and the photocatalyst resulting in significant reduction in the number of active sites on the catalyst surface. It is also noticed that when the initial leachate concentration is high, the number of the active sites are decreased because of their competitive adsorption on the TiO2 particles; while on the other hand, during the light intensity illumination period, the OH radicals formed on the catalyst surface are remaining constant as evidenced by constant hydroxyl production rate. Thus, the reactive O2 attacking the contaminants molecules decrease and simultaneously the overall photodegradation efficiency also decrease dramatically. The plot of the apparent reaction rate constant versus the initial leachate concentration exhibits almost a quadratic behaviour which has an optimum value at concentration of 50 mM. Finally, it was found that the degradation rate constant increased with O2 partial pressure until a maximum was obtained around 50% O2/N2 of gas feed composition. The drop in the rate beyond 50% can be explained by the fact that the dissolved oxygen molecular oxygen is strongly electrophilic and thus increasing the dissolved oxygen content probably reduced electron-hole recombination rate and hence the system was able to maintain favourable charge balance necessary for the photocatalytic-redox process. Moreover, in the presence of excess O2, the photocatalyst surface may become highly hydroxylated to the point of inhibiting the adsorption of organic species causing decrease in the degradation rate. Effect of upflow co-current and counter current continuous operation mode were performed in the 18-litre bubble column photoreactor for the photooxidation degradation tratment of the dump-site landfill leachate. The best situation is liquid flow rate at 800 mL min-1 and total gas flow rate at 5 Lmin-1 for the counter current operation, while for the up-flow co-current operation, the best situation is liquid flow rate at 600 mL min-1 and total gas flow rate at 5 Lmin-1

The thesis constitutes an investigation into the production of floating photocatalytic particles (FPP) as a low cost, low carbon footprint and chemical-free wastewater treatment. It is anticipated that this approach would be particularly attractive for developing countries where it could reduce incidences of disease and pollution. The particles were manufactured from cocoa butter (CB), and contained either photocatalytic nanoparticle titanium dioxide TiO2 (P25) or silver-doped TiO2 (0.5% w/w). The photocatalytic activity of the particles was evaluated by means of the decolourisation of the dye indigo carmine (IC). Three arrangements were used; small scale treatment using Petri dishes, an 1800 ml batch-recirculation photoreactor and an 8 litre UV contactor. Membrane emulsification (ME) was the technique used here to generate particles of controlled size. The particles were in effect what are known as Pickering emulsions in which the solid fat core (CB) was stabilised by TiO2 nanoparticles, resulting in composite particles that float easily and can receive incident light to generate highly reactive free radical species. The FPPs were characterised by FEGSEM and EDs mapping analysis, and the images obtained displayed a spherical structure with a rough outer surface, and the EDs showed a good coverage of TiO2 on the surface of at a maximum loading of 10% w/w. Tests were conducted to assess the stability of the particles when used in repeated cycles. Reuse of the particles caused a significant drop of photodegradation activity after four cycles to 42% of that of freshly prepared particles. The correlation of photocatalytic activity with silver dosage was also investigated. The highest photocatalytic activity was achieved at 0.5 wt. % of silver doped TiO2 and was some 10% greater than for un- doped particles. The organic carbon release resulted from TOC analysis for the FPPs that were exposed to UV light for 8.5 hr in water was less than 1 wt. %. First order reaction kinetics were exhibited during decolourisation of IC dye with respect to the initial dye concentration, radiation intensity, percentage coverage of the liquid surface by the FPPs, and the catalytic loading. For a static system (i.e. no forced convection), the most effective surface coverage was identified as being in the range of 60 to 80%. A linear source spherical emission model (LSSE) was adopted to estimate the intensity of the incident radiation on the surface of the FPP layer in the photoreactor and validated. In addition, a preliminary kinetic model to describe of the effect of the photocatalytic active surface concentration of TiO2 as well as the efficient intensity flux in the kinetic model was developed for the FPP layer photoreactor.

The length of ZnO nanotip can be controlled by the deposition time, and the crystal of ZnO nanotip can be enhanced by a thermal annealing at 300oC in this study.The thickness of TiO2 on ITO/glass also can be controlled by the deposition time in this investigate. There are three major parts in this study : 1. (1). The control of thickness of TiO2 film and length of ZnO nanotip and (2). the difference of their photocatalytic activities are two major parts. 2. The relationship between the surface area and the photocatalytic activities of TiO2 powder (P25) and film. 3. The improvement of photocatalytic activity was utilized by the hetrojunction of ZnO nanotip/TiO2 and TiO2/ZnO nanotip, and the P25 is used as a reference for all measurements.

Crystalline TiO2 nanoparticles were synthesized by hydrolysis of titanium (IV) isopropoxide (TTIP) in the Aerosol OT (AOT)¡Ðcyclohexane microemulsion at controlled temperature. The influence of various reaction conditions, such as mixing energy ( ), [AOT] concentration (W), [TTIP] concentration (R), temperature (T), and aging (t) on the particle size were investigated. The nano-TiO2 particles were characterized for specific surface area (Brunauer-Emmett-Teller, BET) in addition to X-ray diffraction (XRD) and X-ray spectroscopy (XPS) as to determine the particle size, crystalline state, chemical composition, surface charge, and binding energy. The photocatalytic activity was assessed using methylene blue as probe. Results showed that the particle size was in the range from 13.7 to 31.4 nm based on BET measurements. The size of the particle grows with mixing energy until log ( ) = 2.02; further increase in mixing rate caused particle breakup. In micelle solution, the particle size decreased with increase in W. In true solution the particle size increased with W. However, increase in R increased the particle size which reached a maximum value at a critical value of log R = -0.26, then decreased upon further increase in R. The activation energy (Ea) was calculated using Arrenhius plot and a value of -5.96 and -2.17 kJ mol-1 was obtained. Results of particle size analysis from XRD and BET were consistent with each other. Crystalline pattern was proved to be anatase. Furthermore, the photocatalytic activity appeared to optimum with particle size between 22.0-25.1 nm and best crystalline pattern. Titanium dioxide (TiO2) synthesized using the thermal hydrolysis method in our laboratory was used as the photocatalyst in this study to degrade low concentration phenol in aqueous solution. A 150 mL batch reactor was used to carry out the degradation of 0.385 mM phenol solution (pH = 6.5) in room temperature (25 oC) with 0.5 g L-1 TiO2 and irradiated with 10.8 mW cm-2 light intensity for 8 hours. Major intermediate products include hydroquinone (HQ) with the highest quantity followed by catechol (CA), p-benzoquinone (BQ), resorcinol (RES); tri-hydroquinone (THQ) is the secondary intermediate. The by-products consist of 6 organic acids including the six-carbon trans, trans-muconic acid (t,t-MA), the four-carbon maleic acid (MA), the three-carbon propionic acid (PA), the two-carbon oxalic acid (OA) and acetic acid (AA) as well as the one-carbon formic acid (FA). Among these acids, oxalic acid is the most abundant followed by formic acid; the six-carbon t,t-MA is one of the by-products with a lagged formation period. The pathway of intermediate product formation was mathematically calculated and simulated using first-order reaction kinetics models. The reaction rate constants were statistically calculated using functions provided in Microsoft Excel 2003; the simulated results show that the predicted and measured concentrations of the reactant and products in samples collected at various times are consistent.

Semiconductor-based heterogeneous photocatalysis, as one of the advanced oxidation processes that makes use of semiconductors and inexhaustible solar light, has recently been extensively studied and applied to water decontamination. However, due to low light absorption efficiencies and severe electron-hole recombination, modifications on semiconductor structures are required in order to enhance their photocatalytic performance. Heterogeneous photocatalyst composites, taking advantage of the improved light absorption efficiency as well as the facilitated electron-hole separation at the interface between different semiconductors, have been proven to be a promising strategy. In this study, novel NaNbO3/Bi2WO6 photocatalyst composites with a type-II heterogeneous alignment were successfully prepared via a facile wet impregnation method. The as-prepared photocatalysts were characterized by powder X-ray diffraction (XRD), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), diffuse reflectance UV-Vis spectroscopy (DRS), photocurrent (PC) and electrochemical impedance spectroscopy (EIS) analyses. The 30 wt% NaNbO3/Bi2WO6 composite exhibited the best performance for degrading an RhB (rhodamine B) aqueous solution under visible light irradiation (λ > 410 nm), which was ca. 40 times and ca. 2.5 times that of the pristine NaNbO3 and Bi2WO6, respectively. The improved photocatalytic activity may be attributed to the enhanced electron-hole separation efficiency in Bi2WO6 with the assistance of NaNbO_3, as well as the dye-sensitization effect of RhB itself. Radical quenching experiments revealed that h+ played the predominant role, and O2•- functioned as well to some degree. The produced intermediates during the reaction and RhB degradation pathway were speculated and investigated as well. The excellent stability and reusability were verified by repetitively running for five times. Based on experimental results, a plausible functioning mechanism was proposed. Effects of several operation parameters on the catalyst performance including initial RhB concentration, catalyst dosage, reaction temperature and initial pH were also discussed. This study provides solid evidence for NaNbO3 to be a promising candidate for photocatalysis and gives out a novel photocatalytic mechanism of Bi2WO6-based type-II heterostructures.