The room temperature photocatalytic oxidation of carbon monoxide in excess air was examined over silica/titania and 0.1%palladium/silica/titania catalysts under UV irradiation. The experiments were conducted in batch re-circulated reactor with the initial 1000 ppm carbon monoxide in air and 0.5 g catalyst charge and the conversion of carbon monoxide to carbon dioxide was followed by FT-IR spectro-photometer. The change in gas composition in dark and under 36 Watts of UV irradiation exposed to a catalyst area of 12.4 centimeter square indicated both adsorption of carbon monoxide and conversion of carbon monoxide to carbon dioxide over the catalyst samples. The effect of catalyst composition (silica/titania) ratio and the presence of palladium oxide were investigated. The catalyst samples were synthesized by sol-gel technique and all samples were hydrothermally treated before calcination in air. The catalyst samples were characterized by XRD and nitrogen adsorption techniques. XRD results indicated that titania is comprised of pure anatase phase and palladium oxide preferantially dispersed over titania. BET surface area of the samples were observed to increase with silica loading and the BJH results showed isotherms of Type V v with H2 hysteresis loops. The highest carbon monoxide adsorption rate constant was achieved with pure silica with the highest surface area. Photocatalytic activity measurements indicated that carbon monoxide in excess air can be successfully oxidized at room temperature over the titania photocatalyts. Higher physisorption was observed over higher silica containing samples and higher oxidation activity was observed with increasing titania/silica ratio. The optimum titania/silica ratio was determined by the titania content and surface area of catalyst. The activity tests were also indicated that the addition of palladium oxide phase synergistically increased the adsorption and oxidation activity of the catalysts.

Titanium Dioxide (TiO2) emerged as one of the most popular photocatalysts since 1970's. However, its photocatalytic activity requires UV irradiation due to its large band gap unless further functionalization or modifications are performed. Furthermore, recovery issue has always been a major drawback, if the more effective form nano particles are utilized. The key objectives of this research were synthesizing new TiO2 based photocatalyst systems that are effective with both the UV and the visible light while utilizing novel superior environmentally friendly techniques enabling development of nano-structured photocatalysts that can be easily recovered. In this dissertation research, highly porous nano-structured TiO2/WO3/Fe3+ aerogel composite photocatalyst are prepared, characterized, and tested for model photocatalytic reactions. The photocatalyst structure is tailored to capture environmental pollutants and enable their decomposition in-situ under both UV and visible light through photodecomposition to smaller benign substances. A novel and green method is applied to prepare unique surfactant templated aerogel photocatalysts with highly porous nano-structure, high surface area, and tailored pore size distribution. Sol-gel process followed by supercritical fluids extraction and drying allowed synthesis of highly porous composite TiO2/WO3 aerogel. The surfactant template was completely removed with the aid of a supercritical solvent mixture followed with heat treatment. Fe3+ ion was incorporated within the composite aerogel photocatalyst as dopant either at the sol-gel co-precipitation step or at a subsequent supercritical impregnation process. Supercritical drying followed with heat treatment results in titanium dioxide with the most profound anatase crystal structure. Neutral templates were used to further enhance retention and tuning of the nano-pore structure and the surface properties. The Nitrogen adsorption-desorption isotherms methods were used to follow the removal of solvents and templates as well as tracking the textural properties of the synthesized aerogel. Surfactant-templated aerogels, which show remarkable thermal stability and uniform pore size distribution, exhibit specific surface areas three times more than the highly optimized commercial nano-particles, industry standard TiO2 photocatalyst Degussa P-25, even after heat treatment. The synthesized catalysts were characterized by using SEM, FIB, EDS, XRD, XPS and porosimetry prior to post photocatalytic activity evaluation through a model photocatalytic reaction. The band gaps of the catalysts were also determined by using diffuse reflectance spectroscopy. The model reaction employed Methylene Blue (MB) photo-oxidation under UV and visible light. Resulting aerogel TiO2/WO3/Fe3+ photocatalyst exhibited comparable photocatalytic capability to Degussa P25 under UV light exposure and offered much superior photocatalytic capability under visible light exposure.

Pasaulyje neslopsta susidomėjimas fotokataliziniais procesais, kuriuos siekiama pritaikyti vandens skaidymo į vandenilį ir deguonį, organinių ar neorganinių junginių nukenksminimo technologijose. Fotoelektrocheminis vandens skaidymas į elementus vertinamas kaip vienas perspektyviausių būdų, galinčių ateityje užtikrinti efektyvų atsinaujinančių energijos šaltinių panaudojimą. Kuriant fotokatalizines sistemas, nanostruktūrinis titano dioksidas (TiO2) išlieka viena tinkamiausių ir labiausiai tyrinėtų medžiagų. Tačiau titano dioksidas neaktyvus regimosios spinduliuotės srityje, todėl alternatyva TiO2 fotokatalizatoriui gali būti kitas n-tipo puslaidininkis – volframo trioksidas (WO3). Volframo trioksidui yra būdingos fotochrominės savybės, jis absorbuoja dalį regimosios spinduliuotės. Daugelio tyrėjų nuomone, norint padidinti jo fotokatalizinį aktyvumą, tikslinga kurti mišrius oksidinius katalizatorius arba modifikuoti paviršių kitomis medžiagomis. Atsižvelgiant į literatūroje pateiktus duomenis, šiame darbe buvo siekiama pagaminti aktyvius kompozitinius fotokatalizatorius, kurių pagrindinė sudedamoji dalis yra volframo trioksidas. Darbas skirtas naujų medžiagų, kurios galėtų būti naudojamos fotokataliziniuose ir fotoelektrocheminiuose procesuose, paieškai ir charakterizavimui. Šio darbo tikslas – susintetinti TiO2, Se ir Co–P priedais modifikuotus volframo trioksido katalizatorius, ištirti jų struktūrą, fotokatalizines bei fotoelektrochemines savybes. / Scientific community exhibits a great interest in photocatalytic processes such as water photosplitting or photooxidation of organic substances. The photoelectrochemical splitting of water into hydrogen and oxygen is considered as the very promising pathway in the development of a long-term, sustainable energy economy. Titania (TiO2) still remains to be the most suitable for practical applications. However, using it as a photocatalyst still has some major issues: due to the fast recombination of photogenerated charge carriers, the overall quantum efficiency is relatively low, and titania is mostly sensitive to UV irradiation. Tungsten trioxide (WO3) is another semiconductor which can be employed in photocatalysis. Besides its photochromic properties, it has a smaller band gap than titania and may be activated under visible light illumination. In order to improve the photocatalytic efficiency it may be reasonable enough to combine both titania and tungsten trioxide into one photocatalyst or to modify their surface with various compounds. This work is relevant in the search of new materials suitable for photocatalytic and photoelectrocatalytic processes. The main object of this work was to synthesize active tungsten oxide-based composite catalysts and evaluate their structure and properties. Aim of the work was to synthesize WO3 catalysts modified with TiO2, Se and Co-P additives, to investigate their structure, photocatalytic and photoelectrochemical properties.

This thesis examines the effects of nanoparticle, metal-oxide additives on the burning rate of composite solid propellants. Recent advancements in chemical synthesis techniques have allowed for the production of improved solid rocket propellant nano-scale additives. These additives show larger burning rate increases in composite propellants compared to previous additive generations. In addition to improving additive effectiveness, novel synthesis methods can improve manufacturability, reduce safety risks, and maximize energy efficiency of nano-scale burning rate enhancers. Several different nano-sized additives, each titania-based, were tested and compared for the same baseline AP/HTPB formulas and AP size distributions. The various methods demonstrate the evolution in our methods from spray-dried powders to pre-mixing the additive in the HTPB binder, and finally to a method of producing the additive directly in the binder as a nano-assembly. Burning rate increases as high as 80% at additive mass loadings of less than 0.5% were seen in non-aluminized, ammonium perchlorate-based propellants over the pressure spectrum of 500 psi (3.5 MPa) to 2250 psi (15.5 MPa). Increases in burning rate up to 73% were seen in similarly formulated aluminized propellants. During the past several years, the research team has refined laboratory-scale techniques for quickly and reliably assessing the mixing and performance of composite propellants with catalytic nanoparticle additives. This thesis also documents some of the details related to repeatability, accuracy, and realism of the methods used in the team’s recent nano-additive research; it also introduces the latest techniques for producing propellants with nano-sized additives and provides new burning rate results for the entire scope of additives and mixing methods. Details on the propellant characterization methods with regard to physical and combustion properties are provided. Snapshots from atmospheric propellant combustion videos taken with a Photron FASTCAM SA3 high-speed camera are included along with existing pressure and light-emission responses.

Titania has been the focus of attention for several decades owing to its chemical stability, non-toxicity, inexpensiveness and robust surface chemistry. Its technological applications include use in diverse areas such as photocatalytic reactors, antibacterial coatings, dye sensitive solar cells (DSSC) and more recently the perovskite solar cells to name a few. All of these applications are based on the ability to inject or generate electronhole pairs in titania and transport them to a suitable interface at which they are ejected to either engender a reaction as in photocatalysis or drive a load as in photovoltaics. From a technological perspective it is also important that such science be achieved and controlled in supported titania structures. The research reported in this thesis, thus, started with the development of a process for obtaining adherent titania films by oxidation of sputtered Ti films on stainless steel, a very commonly used substrate. Challenges that had to be overcome included the need to oxidize titanium to obtain the right phase mixture while preventing film cracking or delamination due to compressive stresses generated during anodic oxidation of Ti. During this process of obtaining nanostructured TiO2 through anodization, it was serendipitously discovered that planar TiO2 films obtained by oxidation of sputtered Ti films did significantly better than anodized nanoporous titania in bactericidal studies. This was then replicated in organic dye degradation studies. Analysis of the material showed that this improved performance was due to the unintentional contamination during sputtering by Cu, Zn, Mo possibly due to arcing across brass contacts. This quaternary system was then systematically explored and it was shown that an optimal metastable composition in the Ti- Cu-Mo oxide ternary system performs the best. DFT studies showed that this was due to introduction of shallow and deep states in the band gap that, depending on the level of dopants, either enhances carrier lifetimes or leads to recombination. In continuation of this work on supported titania structures by oxidation of Ti, a novel photoanode for use in dye sensitized photovoltaics was developed by oxidation of Ti foam. This results in an interconnected 3-D network of TiO2 that possess at its core a network of Ti. Such architecture was designed to provide a large surface area for anchoring the sensitizer while simultaneously reducing the distance that charge carriers have to travel before reaching the ohmic contacts to prevent recombination losses. The thesis discusses the preparation of such anodes, the properties of the 3-D oxide and cells, with up to 4% efficiency, developed using such anodes. Reasons for such behaviour and avenues for further exploration to improve cell efficiency will also be discussed.

A fabricação e a caracterização de eletrólitos compósitos Nafion - TiO2, e seu uso em células PEM (Proton Exchange Membrane) operando em temperaturas elevadas (~ 130 ºC) foram estudados. A operação em altas temperaturas da célula PEM traz benefícios, como o aumento da cinética das reações eletródicas, o aumento da cinética de transporte difusional nos eletrodos e o aumento da tolerância da célula ao contaminante monóxido de carbono. O Nafion ®, eletrólito polimérico comumente empregado em células PEM, possui condutividade elétrica dependente da quantidade de água contida em sua estrutura. Desta forma, o aumento da temperatura de operação da célula acima de 100 ºC causa a desidratação do polímero diminuindo acentuadamente sua condutividade elétrica. Para aumentar o desempenho dos eletrólitos operando em altas temperaturas, eletrólitos compósitos (Nafion-TiO2) foram preparados pelo método de conformação por evaporação em molde. A adição de partículas higroscópicas de titânia (TiO2) na matriz polimérica visa melhorar as condições de umidificação do eletrólito em temperaturas elevadas. Três tipos de partículas de titânia com diferentes áreas de superfície específica e formas distintas foram investigados. Compósitos à base de Nafion com adição de 2,5 a 15% em massa de partículas de titânia com forma aproximadamente esférica e com área de superfície específica de até ~115 m2g-1 apresentaram maiores valores da temperatura de transição vítrea do que o polímero. Este aumento melhora a estabilidade do eletrólito durante a operação de células a combustível PEM em 130 ºC. Os compósitos formados a partir da adição de nanotubos derivados de titânia apresentaram pronunciado ganho de desempenho e maior estabilidade térmica em operação de células acima de 100 ºC. Neste caso, a elevada área superficial e a forma dos nanotubos de titânia contribuíram significativamente para o aumento da absorção e da retenção de água do compósito. Por outro lado, as curvas de polarização mostraram um aumento na polarização por queda ôhmica com o aumento da concentração das partículas cerâmicas adicionadas. A morfologia do polímero não foi alterada com a adição de partículas inorgânicas, portanto, o desempenho dos compósitos reflete uma competição entre a adição de uma fase isolante, que diminui a condutividade elétrica, e o aumento da estabilidade térmica ou da retenção de água do compósito. Os eletrólitos compósitos testados provaram serem promissores na aplicação em células PEM em temperaturas acima de 100 ºC. / The fabrication and characterization of Nafion - TiO2 composites, and the use of such electrolytes in PEM (Proton Exchange Membrane) fuel cell operating at high temperature (130 °C) were studied. The operation of a PEM fuel cell at such high temperature is considered as an effective way to promote fast electrode reaction kinetics, high diffusional transport, and high tolerance to the carbon monoxide fuel contaminant. The polymer Nafion® is the most used electrolyte in PEM fuel cells due to its high proton conductivity. However, the proton transport in Nafion is dependent on the water content in the polymeric membrane. The need of absorbed water in the polymer structure limits the operation of the fuel cell to temperatures close to 100 °C, above which Nafion exhibits a fast decrease of the ionic conductivity. In order to increase the performance of the electrolyte operating at high temperatures, Nafion-TiO2 composites have been prepared by casting. The addition of titania hygroscopic particles to the polymeric matrix aims at the enhancement of the humidification of the electrolyte at temperatures above 100 °C. Three types of titania particles with different specific surface area and morphology have been investigated. Nafion-based composites with the addition of titania nanoparticles, in the 2.5-15 wt.% range, with nearly spherical shape and specific surface area up to ~115 m2g-1 were found to have higher glass transition temperature than the polymer. Such an increase improves the stability of the electrolyte during the fuel cell operation at high temperatures. The addition of titania-derived nanotubes results in a pronounced increase of the performance of PEM fuel cell operating at 130 °C. In this composite, the high specific surface area and the tubular shape of the inorganic phase are responsible for the measured increase of both the absorption and retention of water of the composite electrolyte. Nonetheless, the polarization curves of fuel cell using the composite electrolytes exhibited an increase of the ohmic polarization associated with the addition of the insulating titania particles. As the chemical structure of Nafion was observed to be insensitive to the addition of the inorganic particles, the high performance of the composite electrolytes is a result of competing effects: the decrease of the electrical conductivity and a higher thermal stability or water absorption/retention capacity. The experimental results suggest that the Nafion-TiO2 composites are promising electrolytes for PEM fuel cells operating at temperatures above ~100 °C.

Orientador: Yoshitaka Gushikem / Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Quimica / Made available in DSpace on 2018-08-12T12:34:45Z (GMT). No. of bitstreams: 1 Maroneze_CamilaMarchetti_D.pdf: 2513143 bytes, checksum: e060b55725fd3d82055ff22070325cb0 (MD5) Previous issue date: 2008 / Resumo: Este trabalho reporta a preparação, caracterização e aplicação de um novo material carbono cerâmico eletricamente condutor, SiO2/TiO2/Grafite. O método sol-gel foi empregado como procedimento de síntese e permitiu a inclusão de carbono grafite por toda a estrutura porosa do óxido misto SiO2/TiO2. Análises de microscopia eletrônica de varredura (MEV) acoplada com espectroscopia de energia dispersiva (EDS) mostram que os materiais sintetizados apresentam-se altamente homogêneos quanto à distribuição e dispersão dos componentes na matriz, sem indícios de segregação de fase ou da formação de domínios dos óxidos puros. As matrizes apresentaram alta estabilidade térmica, nas quais não se observou a cristalização do TiO2 em temperaturas abaixo de 1000 °C. Os valores de energia de ligação para o nível 2p do Ti obtidos por espectroscopia fotoeletrônica excitada por raios X (XPS) revelam a possível inserção de átomos de Ti em sítios tetraédricos da sílica bem como a existência de ligações Si-O-Ti na interface entre os óxidos. Tais ligações são tidas como as responsáveis pela estabilização e baixa mobilidade do Ti nas matrizes cerâmicas. Imagens de campo escuro obtidas por microscopia eletrônica de transmissão de alta resolução (HRTEM) permitiram observar que os cristalitos de grafite encontram-se dispersos em toda a extensão das partículas, sem localização preferencial. Duas reações químicas foram realizadas entre os grupos Ti-OH presentes na superfície e espécies ácidas como o H3PO4 e SbCl5, dando origem a materiais do tipo SiO2/TiO2/Fosfato/Grafite e SiO2/TiO2/Sb2O5/Grafite, com interessantes propriedades de troca iônica. Estes materiais foram então avaliados e utilizados como substratos condutores na construção de eletrodos carbono cerâmicos que foram modificados quimicamente através da adsorção do corante catiônico azul de meldola. Os eletrodos modificados apresentaram bom desempenho e atividade catalítica frente à oxidação da coenzima b-NADH, reduzindo drasticamente o potencial de oxidação em relação a eletrodos convencionais. O material SiO2/TiO2/Grafite se mostra como uma promissora alternativa no desenvolvimento de sensores eletroquímicos, atuando como um substrato condutor robusto e versátil para a confecção de novos eletrodos de trabalho carbono cerâmicos / Abstract: This work reports the preparation, characterization and application of a new electrically conducting carbon ceramic material, SiO2/TiO2/Grafite. The sol-gel methodology was used as synthesis procedure and allowed the incorporation of carbon graphite all over the porous structure of the mixed oxide SiO2/TiO2. Scanning electronic microscopy (SEM) images coupled to energy dispersive spectroscopy (EDS) showed materials with high degree of homogeneity related to the distribution and dispersion of the components in the matrix, with no evidence of phase segregation or formation of pure oxide domains. The matrices presented high thermal stability, in which we do not observed the TiO2 crystallization bellow the temperature of 1000 °C. The binding energy values for Ti 2p level obtained by X-ray photoelectron spectroscopy (XPS) revealed possible insertion of Ti atoms in tetragonal sites of silica as well as the existence of Si-O-Ti linkages at the interface between the oxides. Such linkages are pointed as the responsible by the stabilization and low mobility of Ti in the ceramic matrix. Dark field high resolution transmission electronic microscopy images allowed us to observe that the graphite crystallites are well dispersed through the particles, with no preferential location. Two chemical reactions were carried out between the Ti-OH groups found on the surface and acidic species H3PO4 and SbCl5, resulting in materials like SiO2/TiO2/Fosfato/Graphite and SiO2/TiO2/Sb2O5/Graphite. These materials were utilized as conducting supports in the construction of carbon ceramic electrodes that were chemically modified by the adsorption of the cationic dye meldola blue. The modified electrodes presented good performance and catalytic activity toward b-NADH oxidation, decreasing drastically the oxidation potential when compared to conventional electrodes. The SiO2/TiO2/Graphite material has shown to be a promising alternative in the development of electrochemical sensors, acting as a robust and versatile conducting substrate for the construction of new carbon ceramic electrodes / Doutorado / Quimica Organica / Doutor em Ciências

Kyoto University (京都大学) / 0048 / 新制・論文博士 / 博士(工学) / 乙第12680号 / 論工博第4082号 / 新制||工||1548(附属図書館) / 29813 / (主査)教授 田中 庸裕, 教授 江口 浩一, 教授 安部 武志 / 学位規則第4条第2項該当

Titanium dioxide and aluminum oxide are conventional materials used in heterogeneous catalysis as catalyst support. The widely used crystalline phase of both supports is the metastable phase (anatase and γ-Al$_2$O$_3$) in which they possess a higher specific surface area compared to the thermodynamically stable phase (rutile and α-Al$_2$O$_3$). However, these phases have better thermal and mechanical stability than anatase and γ-Al$_2$O$_3$. A novel method to induce phase transformation and structural modification of crystalline materials is by applying shock waves. This study aims to experimentally investigate the effects of shock wave treatment on titania and alumina. A pressure-driven shock tube was used in this work to generate the shock waves. Two sets of experiments were carried out for TiO$_2$ and one for Al$_2$O$_3$. Titania samples were prepared in the form of pellets for the first set. Titania and alumina samples were maintained as powder for the second set of experiments. For titania, twenty shocks were applied at nominal temperature and pressure of ~ 1772 K and 23.3 bar in the first set of experiments, while thirty shocks of ~ 1572 K and 66 bar were applied in the second set of experiments. For alumina, twenty shock loadings were applied at the same conditions used for the second set of titania. Characterization techniques, such as XRD, Raman spectroscopy, TEM, SEM, XPS, and N$_2$ physisorption were employed on treated samples in order to understand the effects of shock wave treatment. Partial phase transformation was observed in shock treated TiO2 from Raman spectra and TEM images. Crystallite size reduction was observed in the first set of experiments, while increase in defects was observed by the enhanced Ti$^{+3}$ in XPS spectra in both sets of experiments. Partial phase transformation was also observed in shock treated Al$_2$O$_3$, when mixed with CNF (carbon nanofibers), from XRD patterns and confirmed with XPS. For alumina, TEM and SEM images showed the smallest particles in contact with carbon fibers, while the biggest particles exhibited agglomeration. Physisorption experiments showed a decrease of 40% in surface area and pore collapse.

A titania-supported nickel catalyst was prepared and tested in methanation in order to evaluate its catalytic properties (activity, selectivity and specially, activity loss), and compare it with an alumina-supported nickel catalyst. The titania-supported catalyst did not only show higher stability than alumina, but also presented a different cause of deactivation, carbon formation. In addition, a kinetic model was obtained for the titania-supported catalyst, and a study of the effect of different operating conditions (temperature, composition and partial pressures of synthesis gas and water) on the deactivation rate and carbon formation of this catalyst was performed. / <p><strong></strong> </p>