Over the past few decades there has been great interest in exploring alternatives to conventional separation methods due to their high cost and energy requirements. Membranes offer a potentially attractive alternative as they potentially address both of these points. The overarching theme of this dissertation is to design nanocomposite membranes for processes where existing separation schemes are inadequate. This dissertation focuses on three challenges: 1) designing organic-inorganic hybrid membranes for reverse-selective removal of alkanes from light gases, 2) defect-free inorganic nanocomposite membranes that have uniform pores, and 3) nanocomposite membranes for minimizing protein fouling in microfiltration applications. Reverse-selective gas separations that preferentially permeate larger/heavier molecular species based on their greater solubility have attracted considerable recent attention due to both economic and environmental concerns. In this study, dendrimer-ceramic hybrid membranes showed exceptionally high propane/nitrogen selectivities. This result was ascribed to the presence of stable residual solvent that affects the solubility of hydrocarbon species. Mesoporous silica-ceramic nanocomposite membranes have been fabricated to provide defectless mesoporous membranes. As mesoporous silica is iteratively synthesized in the ceramic macropores, the coating method and the surfactant removal step significantly affected permeance and selectivity. It was also shown that support layers can cause a lower selectivity than Knudsen limit. Membrane fouling which results from deposition and nonspecific adsorption of proteins on the membrane surface is irreversible in nature, and results in a significant decrease in the membrane performance. To address this problem, two approaches were explored: 1) control of the surface chemistry tethering alumina membranes with organic components and 2) development of a novel photocatalytic membrane that exhibits hydrophilicity and can be easily regenerated. Both approaches can offer a viable route to the synthesis of attractive membranes, in that 1) the density of protein-resistant organic groups such as PEG is controllable by changing scaffolds or synthesis conditions and 2) the photocatalytic nanocomposite membranes can open the way for a new regeneration method that is environmentally benign.

In the work, photocatalytical treatment of acetic acid wastewater by nanostructured film of TiO2 under ultra-violet ¡]UV¡^ light illumination was studied. Nanosized TiO2 suspension was prepared by the sol-gel process. Then it was dip-coated on indium tin-oxide¡]ITO¡^glass, which could be used as the anode if applicable. Effects the UV light intensity, UV light wavelength, reactive area of TiO2 film, solution pH, and applied bias voltage on photocatalysis efficiency of acetic acid in term of COD removal were studied in this work. Experimental results have shown that a pseudo first-order kinetics was obeyed in all tests. In this study UV light of 312nm outperformed that of 365nm ¡]15.3¢H vs. 11.0¢H¡^. UV light intensity of 20W was also found to be superior to 10W with COD removal of 11.0¢H against 6.7¢H. COD removal at pH¡×3.18 was about 3.6 times greater as compared with that of at pH=9.98. When the reactive area of TiO2 film was increased to three times, the COD removal was almost doubled. An applied external voltage was found to enhance the removal of COD. When an external voltage of 15V was applied, the COD removal was increased to 84.6¢H. It is ascribed to an external voltage would prevent or lower the extent of electron-hole recombination. In this work, the pseudo first-order reaction rate equation K¡¬=1.7679(COD)-0.7547 was obtained for various concentrations of acetic acid tested.

Mainly used food packaging materials are petro-chemical based polymers which present environmental problems since they are not biodegradable and ecologically sustainable. In this study, biodegradable biofilms are produced from xylan, extracted from cotton stalk which is an agricultural biowaste without nutritional value. Antimicrobial property was given to the biofilms with either titanium dioxide sol-gel coatings or titanium dioxide powder addition into the biofilm forming solutions. The antimicrobial activities of biofilms were tested against Escherichia coli. Among two different sol-gels coated and at different temperatures dried biofilms, BWX and CSX-50 biofilms treated at 120&deg / C and coated with SiO2/TiO2 showed 88&plusmn / 1% and 75&plusmn / 2% antimicrobial activities, respectively. Same samples treated at the same conditions but coated with non-SiO2 added TiO2 sol-gel yielded 63&plusmn / 3% and 63&plusmn / 2% antimicrobial activities, respectively after 2 h black light illumination. So, it was determined that the highest photocatalytic antimicrobial property was achieved with SiO2/TiO2 coated biofilms. Moreover different concentrations of TiO2 powder were integrated into xylan based biofilms and 100% photocatalytic inactivation was gathered at 5% (w/w) TiO2 addition achieved at both biofilms at the end of 90 min black light illumination. Biodegradability properties of the biofilms were investigated in soil burial test during 180 days and 10% (w/w) TiO2 powder added CSX-50 biofilms were recorded to be 91% biodegradable where non-powder added blank biofilms was found to be 95% biodegradable.

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.

Although the high cost of solar cells prevents them being a primary candidate for energy production, great attention has been paid towards them because of the depletion of the conventional energy sources–fossil fuels–and the global warming effect, and the need to provide power to remote communities disconnected from the power grid. To reduce the cost, thin film technologies for silicon solar cells have also been investigated and commercialized, but dye sensitized solar cells (DSSC) have been considered as a promising alternative even for the silicon thin films with efficiency exceeding 10%. Compared with silicon-based photovoltaic devices, DSSCs are quite complex systems that require an intimate interaction among components. Within the last few years, conclusive smart solutions have been provided to improve the efficiency of these cells, with solar efficiency that makes them potential competitors against silicon devices. The most successful systems use titanium oxide as a core material tuned to collect and transmit the electrons generated by the photo-excitation of dye molecules. However, most of the solutions demonstrated so far require a thermal treatment of the TiO2 photoelectrodes at temperatures that preclude using any flexible organic substrate. This treatment prevents development of any roll-to-roll manufacturing process, which would be the only way to achieve cost effective large scale production. In order to overcome this major drawback, a novel synthesis of TiO2 at room temperature is described in the present document. This synthesis leads to 4-6 nm nanocrystalline anatase, the desired phase of titanium oxide for photoactive applications. An intensive study was carried out to explore the properties of these nanoparticles, via a mixture design study designed to analyze the influence of the starting composition on the final TiO2 structure. The influence of a post-synthesis thermal treatment was also explored. This 4 nm nanocrystalline TiO2 exhibits a high specific surface area and a good porosity that fulfills the requirements for an efficient photoanode; a high surface area allows high dye loading, and, hence, increases photocurrent and photo-conversion efficiency. Another important result of this study is the band gap, as it confirmed that nanocrystalline anatase has an indirect band gap and a quantum confinement for a crystal size of less than 10 nm. This result, well-known for bulk materials, had been discussed in some previous publications that claimed the effectiveness of a direct band gap. Following this synthesis and the structural and spectroscopic analyzes carried out in parallel, photocatalytic study was an important tool to further explore the semiconducting properties of this material. Additionally, our material gave very promising results in photocatalytic dye degradation, compared to the commercial products, even if it was not initially synthesized for this application. We assign these performances to the improved crystallinity resulting from thermal activation, without changing the crystal size, and to the ability to optimize the surface. This photocatalytic study gave us insights into the methods that optimize the electronic structure of the titanium oxide. Hence, we decided to thermally activate the nanoparticles before the preparation of films to be inserted into DSSCs. At this stage, as the thermal activation applies to the powder, the resulting material can still be used with flexible substrates. We have successfully integrated these nanoparticles in dye sensitized solar cells. Various organic additives were added to the TiO2 paste used to prepare photoelectrode films, to increase the porosity of the film and have a crack–free film with good attachment to the substrate. We demonstrated that the dye was chemically attached to the TiO2 surface, which led to better electron transport. Different treatment methods (UV and thermal) were applied to the film to cure it from organic additives and improve the electronic connectivity between the particles. When the UV treatment was applied as a single method, i.e. without thermal treatment, the cell performance was lower, but a combination of thermal treatment and UV enhanced this performance. We compared our nanoparticles to the reference material used in most of the studies on DSSC, that is, TiO2 Degussa, with cells prepared the same way. Our nanoparticles revealed higher overall conversion efficiency. As the dye attachment to the TiO2 surface is an important parameter that enhances the cell efficiency, so we checked via ATR-FTIR how the dye attached to the TiO2 surface. In addition, FTIR, UV-Vis, and IV measurements revealed that the amount of dye adsorbed was increased through HCl treatment of the photoelectrode. We also checked the internal resistance of the cell using impedance spectroscopy, and the analysis proved a successful integration of the nanoparticles in dye–sensitized solar cells as there was an increase in both the electron life time and the recombination resistance, and a decrease in the charge transfer resistance compared to the commercial powder.

京都大学 / 新制・課程博士 / 博士(工学) / 甲第23912号 / 工博第4999号 / 新制||工||1780(附属図書館) / 京都大学大学院工学研究科物質エネルギー化学専攻 / (主査)教授 陰山 洋, 教授 阿部 竜, 教授 安部 武志 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DGAM

京都大学 / 新制・課程博士 / 博士(工学) / 甲第23914号 / 工博第5001号 / 新制||工||1781(附属図書館) / 京都大学大学院工学研究科物質エネルギー化学専攻 / (主査)教授 阿部 竜, 教授 安部 武志, 教授 作花 哲夫 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DFAM

Magnetic photocatalysts were synthesised by coating a magnetic core with a layer of photoactive titanium dioxide. This magnetic photocatalyst is for use in slurry-type reactors in which the catalyst can be easily recovered by the application of an external magnetic field. The first attempt at producing this magnetic photocatalyst involved the direct deposition of titanium dioxide onto the surface of magnetic iron oxide particles. The photoactivity of these Fe3O4/TiO2 was lower than that of single-phase TiO2 and was found to decrease with an increase in the heat treatment. These observations were explained in terms of an unfavourable heterojunction between the titanium dioxide and the iron oxide core. Fe ion diffusion from the iron oxide core into the titanium dioxide matrix upon heat treatment, leading to a highly doped TiO2 lattice, was also contributing to the observed low activities of these samples. These Fe3O4/TiO2 particles were found to be unstable, with photodissolution of the iron oxide phase being encountered. This photodissolution was dependent on the heat treatment applied, the greater the extent of the heat treatment, the lower the incidence of photodissolution. This was explained in terms of the stability of the iron oxide phases present, as well as the lower photoactivity of the titanium dioxide matrix. In fact, the observed photodissolution was found to be induced-photodissolution. That is, the photogenerated electrons in the titanium dioxide phase were being injected into the lower lying conduction band of the iron oxide core, leading to its reduction and then dissolution. Thus, the approach of directly depositing TiO2 onto the surface of a magnetic iron oxide core proved ineffective in producing a stable magnetic photocatalyst. The introduction of an intermediate passive SiO2 layer between the titanium dioxide phase and the iron oxide phase inhibited the direct electrical contact and hence prevented the photodissolution of the iron oxide phase. Improvements in the photoactivity were seen to be due to the inhibition of both the electronic and chemical interactions between the iron oxide and titanium dioxide phases. Preliminary optimisation experiments revealed that a thin SiO2 layer is sufficient for inhibiting the photodissolution. The thickness of the TiO2 coating was found not to have a significant effect on the photocatalytic performance of the coated particles. Finally, heat treating for 20 minutes at 450??C was sufficient for converting the titanium dioxide into a photoactive phase, longer heating times had no beneficial effect on the photoactivity.

Submitted by Jos? Henrique Henrique (jose.neves@ufvjm.edu.br) on 2018-07-27T21:01:57Z No. of bitstreams: 2 license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) tatiana_santos_andrade.pdf: 1604049 bytes, checksum: bb2c3cf0ac4aa6046bb0b61a72490f8e (MD5) / Approved for entry into archive by Rodrigo Martins Cruz (rodrigo.cruz@ufvjm.edu.br) on 2018-10-05T19:08:11Z (GMT) No. of bitstreams: 2 license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) tatiana_santos_andrade.pdf: 1604049 bytes, checksum: bb2c3cf0ac4aa6046bb0b61a72490f8e (MD5) / Made available in DSpace on 2018-10-05T19:08:11Z (GMT). No. of bitstreams: 2 license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) tatiana_santos_andrade.pdf: 1604049 bytes, checksum: bb2c3cf0ac4aa6046bb0b61a72490f8e (MD5) Previous issue date: 2018 / Com a crescente relev?ncia da produ??o do biodiesel no cen?rio atual, intensifica-se tamb?m a gera??o de glicerol bruto. O glicerol ? formado em abund?ncia nessa cadeia produtiva, representando 10% em peso do produto final. Dessa forma, a fim de permitir maior competitividade para a ind?stria do biodiesel, faz-se imprescind?vel a investiga??o por alternativas que visem o aproveitamento desse subproduto. Entre as poss?veis transforma??es promissoras para o glicerol bruto, encontra-se o emprego de c?lulas fotoeletroqu?micas. Nessas c?lulas, solu??es aquosas de glicerol s?o convertidas em hidrog?nio gasoso quando energia luminosa suficiente ? incidida sobre o fotocatalisador. Apesar do grande potencial das c?lulas fotoeletroqu?micas para o aproveitamento do glicerol, o desafio prevalecente ? sintetizar um fotocatalisador que gere uma alta corrente fotovoltaica nas condi??es envolvidas, e tenha uma alta estabilidade e capacidade de absor??o da luz v?sivel. Neste trabalho, sintetizou-se fotocatalisadores ? base de BiVO4, WO3 e V2O5 por m?todo drop coating, a fim de avaliar seu potencial emprego em c?lulas fotoeletroqu?micas em solu??es de glicerol. As propriedades fotoeletroqu?micas dos materiais foram investigadas por voltametria c?clica, imped?ncia eletroqu?mica, Mott-Schottky, cronoamperometria e cronopotenciometria em solu??es de Na2SO4 e Na2SO3. Al?m disso, caracterizou-se os materiais por reflect?ncia difusa (DRS), Difra??o de Raios-X (DRX) e microscopia eletr?nica de varredura (MEV). Os resultados mostram que as heterojun??es sintetizadas s?o fotocatalisadores eficientes para clivagem da ?gua. Particularmente, a heterojun??o de BiVO4/WO3/V2O5 se destaca pela gera??o de alta corrente fotovoltaica e boas propriedades fotoeletroqu?micas, mostrando que a jun??o dos tr?s materiais foi realizada com ?xito. Testes em solu??es de glicerina geraram resultados ainda melhores, enaltecendo o desempenho dessa heterojun??o em c?lulas fotoeletroqu?micas para aproveitamento de glicerol. / Disserta??o (Mestrado) ? Programa de P?s-gradua??o em Biocombust?veis, Universidade Federal dos Vales do Jequitinhonha e Mucuri, 2018. / The growing relevance of biodiesel production in the current scenario, it also intensifies the generation of crude glycerol. Crude glycerol is formed in abundance in this productive chain, representing 10% by weight of the final product. Thus, in order to allow greater competitiveness for biodiesel industry, it is essential to search for alternatives that aim at new applications for this by-product. Among possible promising transformations for crude glycerol, it can be used in photoelectrochemical cells. In these cells, aqueous solutions of glycerol can be converted into gaseous hydrogen if sufficient light energy is irradiated on the photocatalyst. Despite the great potential of photoelectrochemical cells, the most challenge issue is to synthesize a photocatalyst that generates a high photovoltaic current, has a good stability and excellent light absorption capacity. In this work, photocatalysts based on BiVO4, WO3 and V2O5 were synthesized by drop coating technique, in order to evaluate their potential in photoelectrochemical cells containing glycerol aqueous solutions. To evaluate their photoelectrical properties, electrochemical impedance, Mott-Schottky, chronoamperometry and chronopotentiometry were performed in Na2SO4 and Na2SO3 solutions. In addition, the semiconductors were characterized by diffuse reflectance spectroscopy (DRS), X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results show that the heterojunctions formed are promising photocatalysts. Particularly, the BiVO4/WO3/V2O5 heterejunction stands out for the generation of high photovoltaic current and good properties, showing that this triple junction was successfully made. Tests in glycerol solutions generated even better results, highlighting the performance of this material for photoelectrochemical cells using glycerol.

Kyoto University (京都大学) / 0048 / 新制・課程博士 / 博士(工学) / 甲第13834号 / 工博第2938号 / 新制||工||1434(附属図書館) / 26050 / UT51-2008-C750 / 京都大学大学院工学研究科物質エネルギー化学専攻 / (主査)教授 井上 正志, 教授 江口 浩一, 教授 田中 庸裕 / 学位規則第4条第1項該当