Titanium dioxide (TiO2) is an important semiconducting metal oxide and is expected to play an important role in future applications related to photonic crystals, energy storage, and photocatalysis. Two aspects regarding the combustion synthesis have been investigated; scale-up in laboratory synthesis and advanced nanoparticle synthesis. Concerning the scale-up issue, a novel curved wall-jet (CWJ) burner was designed for flame synthesis. This was achieved by injecting precursors of TiO2 through a central port into different flames zones that were stabilized by supplying fuel/air mixtures as an annular-inward jet over the curved wall. This provides a rapid mixing of precursors in the reaction zone with hot products. In order to increase the contact surface between the precursor and reactants as well as its residence time within the hot products, we proposed two different modifications. The CWJ burner was modified by adding a poppet valve on top of the central port to deliver the precursor tangentially into the recirculating flow upstream within the recirculation zone. Another modification was made by adopting double-slit curved wall-jet (DS-CWJ) configuration, one for the reacting mixture and the other for the precursor instead of the central port. Particle growth of titanium dioxide (TiO2) nanoparticles and their phases were investigated. Ethylene (C2H4), propane (C3H8), and methane (CH4) were used with varying equivalence ratio and Reynolds number and titanium tetraisopropoxide (TTIP) was the precursor. Flow field and flame structure were quantified using particle image velocimetry (PIV) and OH planar laser-induced fluorescence (PLIF) techniques, respectively. TiO2 nanoparticles were characterized using high-resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD), Raman Spectroscopy, and BET nitrogen adsorption for surface area analysis. The flow field quantified by PIV consisted of a wall-jet region leading to a recirculation zone, an interaction jet region, followed by a merged-jet region. The modified CWJ burner revealed appreciable mixing characteristics between the precursor and combustion gases within these regions, with a slight increase in the axial velocity due to the precursor injection. This led to more uniformity in particle size distribution of the synthesized nanoparticles with the poppet valve (first modification). The double-slit modification improved the uniformity of generated nanoparticles at a very wide range of stable experimental conditions. Images of OH fluorescence showed that flames are tightly attached to the burner tip and TTIP has no influence on these flames structures. The particle size was slightly affected by the operating conditions. The phase of TiO2 nanoparticles was mainly dependent on the equivalence ratio and fuel type, which impact flame height, heat release rate and high temperature residence time of the precursor vapor. For ethylene and methane flames, the anatase content is proportional to the equivalence ratio, whereas it is inversely proportional in the case of propane flames. The anatase content reduced by 8% as we changed Re between 8,000 and 19,000, implying that the Re has a slight effect on the anatase content. The synthesized TiO2 nanoparticles exhibited high crystallinity and the anatase phase was dominant at high equivalence ratios (φ >1.6) for C2H4, and at low equivalence ratios (φ <1.3) for the C3H8 flame. Concerning advanced nanoparticle synthesis, a multiple diffusion burner and flame spray pyrolysis (FSP) were adopted in this study to investigate the effect of doping/coating on TiO2 nanoparticles. The nanoparticles were characterized by the previously mentioned techniques in addition to thermogravimetric analysis (TGA) for carbon content, X-ray photoelectron spectroscopy (XPS) for surface chemistry, ultraviolet-visible spectroscopy (UV-vis) for light absorbance, inductively coupled plasma (ICP) for metal traces, and superconducting quantum interference device (SQUID) for magnetic properties. Results from multi diffusion burner show that doping TiO2 with vanadium changes the phase from anatase to rutile while doping and coating with carbon or SiO2 does not affect the phase. Doping with iron reduces the band gab of TiO2 particles by reducing the conduction band. FSP results show that iron doping changes the valance band of the nanoparticles and enhances their paramagnetic behavior as well as better light absorption than pure titania, which make these particles good candidates for photocatalytic applications.

Copper-based materials are one of the most promising catalysts for performing transformations of important organic compounds in both academic and industrial operations. However, it is challenging to consistently synthesize highly active and stable copper species as heterogeneous catalysts due to their relatively high surface energy. As a result, agglomeration usually occurs, which limits the catalytic activities of the copper species. The work presented in this dissertation shows different synthetic strategies for obtaining active and stable copper-based materials by modifying chemical/physical properties of copper nanoparticles (NPs). Emphasis is placed on discussing specific catalytic systems, including carbon-supported catalysts (monometallic and bimetallic copper-based heterogeneous catalysts) and titania-supported catalysts, and their advantages in terms of catalytic performance. In recent years, there has been increasing interest in using metal-organic frameworks (MOFs) as a sacrificial template to obtain carbon-supported NPs via a thermolysis process. The advantages of using MOFs to prepare carbon supported nanomaterials are a fine distribution of active particles on carbon matrix without post-synthesis treatments and corresponding increased catalytic activity and stability in many reaction conditions. To better understand the potential of this synthetic approach, MOF pyrolyzed products have been characterized. Then, they were applied as heterogeneous catalysts for several chemical reactions. In particular, the high energy copper-based MOF, CuNbO-1, was decomposed to obtain an amorphous copper species supported on carbon (a-Cu@C). This catalyst was found to be highly active for reduction, oxidation, and N-arylation reactions without further tuning or optimization. Higher catalyst turnover numbers for each of these transformations were obtained when comparing a-Cu@C activity to that of similar Cu-based materials. To improve catalyst performance, a secondary metal can be introduced to create synergistic effects with the parent copper species. In order to gain insights into the role of the second metal, a well-known Cu-MOF, HKUST-1, was doped with nickel, cobalt, and silver solutions, followed by a decomposition process with 2,4,6-trinitrotoluene (TNT) as additive. This additive was used to enhance the rapid thermolysis of the bimetallic MOFs. In these bimetallic systems, the addition of a second metal was found to help in dispersing both metals over the carbon composite support and in influencing the particle size and oxidation state of the metals. Catalytic performance showed that even <1% of a secondary metal increased the rate for nitrophenol reduction. Optimal catalytic performance was achieved using a Ni-CuO@C bimetallic catalyst. Another synthetic strategy for Cu-catalyst preparation involves using the deposition-precipitation method, in which a copper catalyst anchored on a titania support was synthesized at low weight % in order to obtain a single atom catalyst (1-Cu/TiO2). The higher copper loading catalyst, 5-Cu/TiO2, was synthesized as a benchmark catalyst for comparison. The copper structure in the synthesized catalysts was investigated by powder X-ray diffraction (PXRD), Raman, scanning transmission electron microscopy-energy dispersive X-ray spectroscopy (STEM-EDX), X-ray photoelectron spectroscopy (XPS), N2 physisorption and inductively coupled plasma mass spectrometry (ICP-MS) in order to characterize physical and chemical properties. STEM-EDX observations showed single atom copper species less than 0.75 nm in size, as well as nanoparticles with an average diameter of ~1.31 nm. This catalyst was highly active in the reduction of nitro-aromatic compounds with NaBH4 at room temperature. The small to atomic level sizes of the Cu species and multiple oxidation states of Ti species were found to play a crucial role in the catalytic activity.

Tato diplomová práce se zabývá výrobou ultratenkých keramických dutých vláken pomocí metody povlakování namáčením. Příprava keramických dutých vláken je v současnosti limitována rozměrem vnějšího a vnitřního průměru. Aplikace metody povlakování namáčením pro přípravu ultratenkých dutých je nový a technologicky náročný proces vyžadující volbu vhodné šablony a zároveň zvládnutí kontroly parametrů povlakování. Základními zvolenými materiály s vysokým aplikačním potenciálem jsou hydroxyapatit a oxid titaničitý. Samonosná dutá vlákna s tloušťkou stěny pod 1 m byla úspěšně připravena z obou materiálů. Dále byl také popsán proces povlakování namáčením obětovaných šablon. Tato metoda je unikátní, protože umožňuje produkci ultratenkých keramických dutých vláken s vnitřním průměrem pod 100 m a tloušťkou stěny pod 1 m.

The effects of various catalyst synthesis parameters on the photocatalytic degradation kinetics of aqueous methyl orange dye are presented. The four factors investigated were: i) InVO4 concentration, ii) nickel concentration, iii) InVO4 calcination temperature, and iv) ballmilling time. Three levels were used for each factor. Due to the large number of possible experiments in a full factorial experiment, an orthogonal-array experimental design was used. UV-vis spectrophotometry was used to measure the dye concentration. The results show that nickel concentration was a significant parameter, with 90% confidence. The relative ranking of importance of the parameters was nickel concentration > InVO4 concentration > InVO4 calcination temperature > milling time. The results of the orthogonal array testing were used to make samples of theoretically slowest and fastest catalysts. Curiously, the predicted-slowest catalyst was the fastest overall, though both samples were faster than the previous set. The only difference between the slowest and fastest catalysts was the milling time, with the longer-milled catalyst being more reactive. From this result, we hypothesize that there is an interaction effect between nickel concentration and milling time. The slowest and fastest catalysts were characterized using energy-dispersive spectroscopy (EDS), scanning electron microscopy (SEM), x-ray powder diffractometry (XRD), BET surface area analysis, and diffuse-reflectance spectroscopy (DRS). The characterization results show that the fastest catalyst had a lower band gap than the slowest one, as well as a slightly greater pore volume and average pore diameter. The results indicate that fast kinetics are achieved with low amounts of nickel and a long ball milling time. Under the levels tested, InVO4 concentration and the calcination temperature of the InVO4 precursor were not significant.

This thesis deals with the study of several catalysts for the Fischer-Tropsch synthesis in the Biomass-To-Liquid process. In this work two groups of catalysts were tested. On the one hand, two series of catalysts with cobalt loadings of 6 and 12 wt% over SiO2 and some of them containing 5wt% of TiO2 were tested. One the other hand, other two series of mesoporous short channel SBA-15, all of them with cobalt loadings of 12wt% and some with 5wt% of titania. The first series was supported on SBA-15 DeWitte and the second one on SBA-15 Martinez. On the one hand, the influence of water addition to the feed, titania content and cobalt loading to the catalyst and was studied, as well as the consequences of a GHSV. The FT reaction was carried out along 5 periods of 24 hours each, in which conditions such as feed and water content were modified, enabling the study of these parameters. It was found that water provokes an increase of the CO conversion and has a positive kinetic effect on the rate to hydrocarbons. However, this fact reaction is followed by a quick deactivation, enhanced by high water partial pressures. Most of that deactivation is irreversible since it is not completely recovered after water removal. On the other hand, differences between the supports were studied. Some SBA-15 supported catalysts show CO diffusion limitations at longer channel lengths than what applies for conventional 3D porous supports. Titania grafting increases the rate to hydrocarbons, showing positive results for FT catalysts development.

Photocatalysis is an advanced oxidation process for the purification and remediation of contaminated waters and wastewaters, and is advantageous over conventional treatment technologies due to its ability to degrade emerging and recalcitrant pollutants. In addition, photocatalytic disinfection is less chemical-intensive than other methods such as chlorination, and can inactivate even highly resistant microorganisms with good efficacy. Process sustainability and cost-effectiveness may be improved by utilizing solar irradiation as the source of necessary photons for photocatalyst excitation. However, solar-induced activity of the traditionally-used titania is poor due to its inefficient visible light absorption, and recombination of photo-excited species is problematic. Additionally, mass transfer limitations and difficulties separating the catalyst from the post-treatment slurry hinder conversions and efficiencies obtainable in practice. In this research, various strategies were explored to address these issues using novel visible light active photocatalysts. Two classes of carbon-enhanced photocatalytic materials were studied: activated carbon adsorbent photocatalyst composites, and carbon-doped TiO2. Adsorbent photocatalyst composites based on activated carbon and plasmonic silver/silver chloride structures were synthesized, characterized, and experimentally investigated for their photocatalytic activity towards the degradation of model organic pollutants (methyl orange dye, phenol) and the inactivation of a model microorganism (Escherichia coli K-12) under visible light. The adsorptive behaviour of the composites towards methyl orange dye was also studied and described according to appropriate models. Photocatalytic bacterial inactivation induced by the prepared composites was investigated, and the inactivation mechanisms and roles of incorporated antimicrobial silver on disinfection were probed and discussed. These composites were extended towards magnetic removal strategies for post-use separation through the incorporation of magnetic nanoparticles to prepare Ag/AgCl-magnetic activated carbon composites, and the effect of nanoparticles addition on the properties and photoactivities of the resulting materials was explored. Another silver/silver halide adsorbent photocatalyst composite based on activated carbon and Ag/AgBr exhibiting visible light absorption due to both localized surface plasmon resonance and optical band gap absorption was synthesized and its photocatalytic activity towards organics degradation and microbial inactivation was studied. Carbon-doped mixed-phase titania was also prepared and experimentally investigated.

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This collection of studies focuses on a PCO system for the oxidation of a model compound, ethanol, using an adsorption-enhanced silica-Ti02 composite (STC) as the photocatalyst; studies are aimed at addressing the optimization of various parameters including light source, humidity, temperature, and possible poisoning events for use as part of a system for gaseous trace-contaminant control system in closed-environment habitats. The first goal focused on distinguishing the effect of photon flux (i.e., photons per unit time reaching a surface) from that ofphoton energy (i.e., wavelength) of a photon source on the PCO of ethanol. Experiments were conducted in a bench-scale annular reactor packed with STC pellets and irradiated with either a UV -A fluorescent black light blue lamp O·max=365 nm) at its maximum light intensity or a UV -C germicidal lamp O.·max=254 nm) at three levels of light intensity. The STC-catalyzed oxidation of ethanol was found to follow zero-order kinetics with respect to C02 production, regardless of the photon source. Increased photon flux led to increased EtOH removal, mineralization, and oxidation rate accompanied by lower intermediate concentration in the effluent. The oxidation rate was higher in the reactor irradiated by UV -C than by UV-A (38.4 vs. 31.9 nM s-1 ) at the same photon flux, with similar trends for mineralization (53.9 vs. 43.4%) and reaction quantum efficiency (i.e., photonic efficiency, 63.3 vs. 50.1 nmol C02 ~mol photons-1 ). UV-C irradiation also led to decreased intermediate concentration in the effluent compared to UV -A irradiation. These results demonstrated that STC-catalyzed oxidation is enhanced by both increased photon flux and photon energy. The effect of temperature and relative humidity on the STC-catalyzed degradation of ethanol was also determined using the UV-A light source at its maximum intensity. Increasing ii temperature from 25°C to 65°C caused a significant decrease in ethanol adsorption (47.1% loss in adsorption capacity); minimal changes in EtOH removal; and ·a dramatic increase in mineralization (37.3 vs. 74.8%), PCO rate (25.8 vs. 53.2 nM s-1 ), and reaction quantum efficiency (42.7 vs. 82.5 nmol C02 J..Lmol phontons-1 ); intermediate acetaldehyde (ACD) evolution in the effluent was also decreased. By elevating the reactor temperature to 45°C, a -32% increase in reaction quantum efficiency was obtained over the use ofUV-C irradiation at room temperature; this also allowed for increased energy usage efficiency by utilizing both the light and heat energy of the UV-A light source. Higher relative humidity (RH) also caused a significant decrease (16.8 vs. 6.0 mg EtOH g STCs-1 ) in ethanol adsorption and dark adsorption 95% breakthrough times (48.5 vs.16.8 hours). Trends developed for ethanol adsorption correlated well with studies using methanol as the target VOC on a molar basis. At higher RH, ethanol removal and ACD evolution were increased while mineralization, PCO rate, and reaction quantum efficiency were decreased. These studies allowed for the development of empirical formulas to approximate EtOH removal, PCO rate, mineralization, and ACD evolution based on the parameters (light intensity, temperature, and RH) assessed. Poisoning events included long-term exposure to low-VOC laboratory air and episodic spikes of either Freon 218 or hexamethylcyclotrisiloxane. To date, all poisoning studies have shown minimal (0-6%) decreases in PCO rates, mineralization, and minimal increases in ACD evolution, with little change in EtOH removal. These results, while studies are still ongoing, show great promise of this technology for use as part of a trace contaminant control system for niche applications such as air processing onboard the ISS or other new spacecrafts.