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This project studies the generation of crystalline mesoporous structured titanium dioxide (TiO2) using cellulose nanocrystal (CNC) aerogel hard templates for photocatalytic and biomaterial applications. Suspensions of CNCs in water varying in solid loading from 20 mg/mL to 100 mg/mL were prepared and frozen at three different temperatures (-20 °C, -40 °C, or -80 °C) using four combinations of hollow cylindrical molds and mold plates with different thermal conductivities (stainless-steel or glass) placed on different heat conductive and insulative substrates (aluminum, polystyrene foam and cardboard). Frozen samples were then freeze dried to sublimate the ice and render a multiscale and mesoporous structure with a variety of microstructural features, including lamellar sheeting, flakes, ribbons, or striations. Ceramic green bodies are then produced by reacting Titanium isopropoxide with water through several different processes to generate amorphous TiO2 either in-situ in the CNC aerogel or as a suspension for infiltration under varying pressure. Green bodies are dried at room temperature, and the extent of ceramic coating of the template is visually determined using SEM imaging. Once dried, crystalline TiO2 are produced through a two-step heat treatment with a CNC burnout at 270 °C and crystallization and sintering at 500 °C, 600 °C, or 1000 °C. The final crystallinity and phase composition is examined using XRD, and the final porosity is determined using BET. Results have shown the ability to satisfactorily coat aerogels under 10 mm in one dimension with TiO2. These samples have been successfully heat-treated to produce both anatase and rutile phase TiO2 while maintaining the macrostructure of the CNC aerogel. Multiscale porosity has been achieved, and samples heat treated at 1000 °C have achieved structural integrity. / Master of Science / Titanium Dioxide (TiO2) is a common material in today's world used in a range of applications including pigments, sunscreens, and thin films. It is a chemically and physically stable material, making it ideal for some biomedical applications including bone and cell growth scaffolds. TiO2 is also photocatalytic and has been used in photovoltaic cells and water decontamination systems to take advantage of this property. While TiO2 has been effectively implemented in these applications, the multiscale, controllable porous structure required for these applications has proven complicated to generate. To help improve this process, cellulose nanocrystal (CNC) aerogels were investigated as tunable hard templates for porous TiO2. Controlled ice templating through alteration of the freezing conditions followed by freeze drying provided a reliable method for the production CNC aerogels with repeatable micro and macrostructures. Testing multiple methods for coating the template in TiO2 led to the successful replication of the template in a ceramic part. The final TiO2 exhibited multiscale porosity with micro and macrostructures matching those of the CNC aerogel template. These parts can be tailored to fit a desired application by controlling the structure of the aerogel.

京都大学 / 0048 / 新制・課程博士 / 博士(エネルギー科学) / 甲第18612号 / エネ博第308号 / 新制||エネ||63(附属図書館) / 31512 / 京都大学大学院エネルギー科学研究科エネルギー応用科学専攻 / (主査)教授 平藤 哲司, 教授 馬渕 守, 教授 土井 俊哉 / 学位規則第4条第1項該当 / Doctor of Energy Science / Kyoto University / DGAM

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Due to an increase of human activity, an increase health risk has emerged from the presence of pollutants in the environment. In the transition to renewable and sustainable life style, treatment of pollutants could support the shifting societies. A motivation behind material research for environmental applications is to maximize the efficiency of the materials to alleviate environmental pollution. In the case of titania, an increase of ultra-violet light absorption is needed to overcome its bandgap to produce reactive radicals, which is the basis for photocatalysis. It has been hypothesized that photonic crystal can enhance titania photocatalysis. They are structures made of at least two dielectrics with a high refractive index contrast, ordered in a periodic fashion. For a strong contrast, photonic band gaps emerge. The effect of the photonic band gap is to force complete reflection of the incoming light within its range and multiple internal reflections at its edges. By combining photonic and electronic band gap positions, it is possible to increase the absorption at the photonic band gap edges. In this thesis, fabrication method and structural analysis of titania and alumina/titania photonic structures were presented. A thorough optical analysis was performed at all steps of fabrication – beyond what previously has been reported. The photocatalytic activity was measured with two setups. Fourier Transform Infrared spectroscopy combined with arc lamps and bandpass filters was used to monitor the degradation of stearic acid in ambient air. A home-built setup was used to degrade methylene blue in solution with ultra-violet illumination. The results in this thesis show in general no correlation of the photocatalytic activity to the photonic band gap position, even though absorbance data displayed an increase absorption in this energy range. A more controlled environment might show the effect of the structure, as seen in some of the experiments.

Nanotubular titanates were synthesized by a simple methodology using a commercial TiO2 (Degussa P25 containing anatase and rutile phases) and a base (KOH) solution. Prior to the removal of KOH, the samples of TiO2 were aged for three different time intervals (0, 2 days, 61 days). The freshly prepared synthetic samples were characterized for their structural and morphological properties by BET, XRD, Raman, TEM, HRTEM, EDX and SEM. Both TEM and SEM analysis revealed that ageing time influenced the tubular structure and morphology of the new materials. Raman and surface analysis data also showed that ageing time affected both the structural and surface properties of TiO2. The XRD results showed that the crystallinity of the TiO2 decreased with increasing ageing time. Energy dispersive Xray spectroscopy (EDX) showed that the tubes derived from TiO2 are comprised of potassium, titanium and oxygen. Catalysts A, B and C were prepared by the addition of 1 wt% Pd (wet impregnation) to the titanate formed after ageing of the TiO2 in KOH for 0, 2 and 61 days, respectively. The catalysts were tested for the vapour phase hydrogenation of phenol in a fixed-bed micro reactor within the temperature range of 165 to 300oC under atmospheric pressure. Of the three catalysts, catalyst B showed the best activity (conversion 97%) and total selectivity to cyclohexanone (99%). In contrast, catalyst C, which showed a moderate activity favoured selectivity to cyclohexanol. These results are attributed to differences in surface morphologies between the two catalysts B and C, associated with the surface area and a change in the surface acid-base properties. Catalyst B also showed a higher resistance towards deactivation and maintained a higher total selectivity to cyclohexanone than did catalyst C. A hydrothermal treatment of NaOH and TiO2 was employed to prepare two materials, TiO2-B and TiO2-C with relatively small crystallite size and large specific surface area. The hydrogenation of phenol was used to evaluate the activity of the catalysts Pd/TiO2-B and Pd/TiO2-C. The reaction proceeds in a single step and involves the formation of a partially hydrogenated product, namely cyclohexanone. The larger surface area catalyst (Pd/TiO2-C, 89 m2/g) showed better activity and selectivity to cyclohexanone than its counterpart (Pd/TiO2-B, 45 m2/g). The catalyst activity showed significant dependency on the surface area whereas the selectivity was greatly influenced by surface basicity. Titania derived nanotubes synthesized by treating P25 Degussa TiO2 with a concentrated KOH solution and aged for 2 days was used as a catalyst support for the hydrogenation of o-chloronitrobenzene (O-CNB) with Pd as the active phase. The vapour-phase hydrogenation of O-CNB was carried out in ethanol at 250 oC and atmospheric pressure over a Pd/TiO2 derived nanotube catalyst (Pd/TiO2-M). Pd/TiO2-M gave complete conversion (100%) of O-CNB with a selectivity to orthochloroaniline (O-CAN) of 86 %. The stability of the Pd/TiO2 catalyst was tested over 5 hours during which time the conversion slowly dropped to 80 % (selectivity 93 %) due to poisoning. TPR analysis revealed the existence of a strong palladium-support interaction and this was found to be crucial to the overall activity of the catalyst. It has been found that gold supported on potassium titanate, KTiO2(OH) can, under some circumstances, exhibit a superior performance for the oxidation of carbon monoxide, relative to that obtained with titania as a support. It appears that the dispersions of gold on the two types of support are sufficiently similar that other factors are responsible for the improved activity noted. It may be that the higher basic character and detailed structural features of the titanate surface play a role. The effect of the addition of alkali metal ions on the anatase to rutile transformation of titanium dioxide (P25 Degussa) was investigated using X-ray diffraction, Raman spectroscopy, and surface area measurements. Both Li and Cs ions accelerated the anatase to rutile transformation whereas Na and K ions did not show any effect. Furthermore, the effect was more pronounced after addition of the Li ions so that the transformation temperature dramatically decreased from ~800 oC for commercial TiO2 to ~600 oC. The surface area of the TiO2 material decreased with sintering due to the increase in crystalline size. Moreover, the acceleration of the transformation occurred at lower temperatures and at higher Li content. Mesoporous nanocrystalline TiO2 (HSA TiO2) was prepared by hydrothermal treatment of TiO2 with NaOH. The material was very amorphous and underwent the phase transformation from amorphous to anatase phase and subsequently from anatase to rutile phase with sintering. The anatase to rutile transformation was delayed after doping and grain growth was inhibited. After sintering at 800 oC the material (HSA TiO2) still contained a significant amount of the anatase phase. The complete transformation only occurred at ~1000 oC. The esterification of benzoic acid and butyric acid with propanol over alkali metal ions supported on TiO2 was investigated. K/TiO2-D showed the highest conversion for both benzoic acid and butyric acid. The selectivity to propylbenzoate and propylbutyrate was influenced by the basic nature of the catalysts. Butyric acid was found to be more reactive than benzoic acid. The difference in reactivity was explained in terms of steric and inductive effects. The differences in boiling points and pH values were also considered.

Water is a vital natural resource. To develop more sustainable water systems, we must focus efforts on the removal of persistent contaminants. Aqueous organic contaminants include azo dyes, halogenated organics (e.g. pesticides), and algal and bacterial metabolites. The latter are common to surface waters and freshwater aquaculture systems and can cause taste and odor problems. Two of the principal organoleptic compounds are geosmin and 2-methylisoborneol (MIB). Traditional oxidation treatment methods, utilizing chlorine, hydrogen peroxide, and potassium permanganate, have been employed with varying levels of efficacy for removal of these and other organic contaminants. Advanced Oxidation Processes (AOPs) have greater potential for the removal of persistent contaminants than traditional methods due to their higher pollutant removal rates, their ability to degrade a variety of organic material, and their ability to completely mineralize compounds [1]. An emerging AOP technology is the use of titania based photocatalysts for water treatment. Titanium dioxide (TiO2) is an effective, inexpensive, and stable photocatalyst used for the decomposition of aqueous organics. Titania is primarily activated by the ultraviolet portion of the spectrum due to its energy band gap of 3.0-3.2 eV (depending upon crystalline structure). Photocatalytic efficiency can be enhanced or tuned through the use of semiconductor dopants and the variance of titania crystal structure (i.e. anatase to rutile ratios). Metal oxides, like indium vanadate (InVO4), may enhance reaction rates through new interfacial reaction sites and electron scavenging, transport, and storage. InVO4 has been shown to have four sub-bandgap transitions, of which three are in the visible range [2]. In this work, the synthesis of InVO4-TiO2 composite semiconductors is examined to shift photo-initiation into the visible portion of the spectrum. Parametric studies of the visible spectrum photodegradation of methyl orange, an azo dye, and 2-chlorophenol provide a basis for analysis. Methyl orange was utilized to ascertain the effect of pure and mixed phase titania in the semiconductor composites. The TiO2 photodegradation of geosmin and MIB has been previously demonstrated in small-scale batch slurry reactions. Slurry systems require the downstream separation of catalyst from the liquid. Laboratory trials use centrifugation or micro-filtration. Alternatively, immobilization of the photocatalyst could allow scale-up of the process. Here, titania was immobilized on glass plate substrates using an ethanol spray technique. Finally, naturally tainted waters may contain a number of constituents in addition to the target compounds. In recirculating aquaculture systems, the water contains natural organic matter (NOM), ammonia, nitrite/ nitrate, and carbonate species. These constituents may block light penetration, block reaction sites, scavenge hydroxyl radicals, or affect the surface chemistry of the catalyst. Further, geosmin and MIB concentrations are extremely low, in the ppt range. Naturally tainted waters from MOTE Marine Laboratory Aquaculture Research Park are treated in the laboratory and in situ to demonstrate TiO2 degradation efficiency for trace concentration geosmin and MIB degradation in a complex water matrix.

The aim of the research presented in this thesis was to increase the understanding of the interaction between polymeric dispersants and titania pigment particles. In particular, the effects of dispersants of varied functionalities on the pigment dispersion behaviour in both aqueous suspension and dry paint film were investigated. / thesis (PhDEng(MineralsandMaterials))--University of South Australia, 2004.

Presented in this thesis is a study of the effects of nano-sized particles used as a catalytic additive in composite solid propellant. This study was done with titanium oxide (titania)-based particles, but much of the findings and theory are applicable to any metal oxide produced by a similar method. The process required for efficiently producing larger batches of nanoparticle additives was seen to have a significant impact on the effectiveness of the additive to modify the burning rate of composite propellant consisting of ammonium perchlorate (AP) and hydroxyl terminated polybutadiene (HTPB). Specifically, titania was seen to be both an effective and ineffective burning rate modifier depending on how the nanoparticle additive was dried and subsequently heat treated. Nanoadditives were produced by various synthesis methods and tested in composite propellant consisting of 80 percent AP. Processability and scale-up effects are examined in selecting ideal synthesis methods of nanoscale titanium oxide for use as a burning rate modifier in composite propellant. Sintering of spray-dried additive agglomerates during the heat-treating process was shown to make the agglomerates difficult to break up during mixing and hinder the dispersion of the additive in the propellant. A link between additive processing, agglomerate dispersion mechanics and ultimately catalytic effect on the burning rate of AP/HTPB propellants has been developed by the theories presented in this thesis. This thesis studies the interaction between additive dispersion and the dispersion of reactions created by using fine AP in multimodal propellants. A limit in dispersion with powder additives was seen to cause the titania catalyst to be less effective in propellants containing fine AP. A new method for incorporating metal oxide nanoadditives into composite propellant with very high dispersion by suspending the additive material in the propellant binder is introduced. This new method has produced increases in burning rate of 50 to 60 percent over baseline propellants. This thesis reviews these studies with a particular focus on the application and scale-up of these nanoparticle additives to implement these additives in actual motor propellants and assesses many of the current problems and difficulties that hinder the nanoadditives’ true potential in composite propellant.

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