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.

京都大学 / 新制・課程博士 / 博士(工学) / 甲第24237号 / 工博第5065号 / 新制||工||1791(附属図書館) / 京都大学大学院工学研究科分子工学専攻 / (主査)教授 田中 庸裕, 教授 佐藤 啓文, 教授 阿部 竜 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DFAM

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QCM sensor is a response to a kind of broad spectrum, high sensitivity, and simple structure, low-cost detection device, and particularly its quality as a type of gas sensor is widely used. With the successful oscillation in liquid phase, QCM sensor has been involved in the application analytical chemistry, surface chemistry, biochemistry and environmental monitoring side and many other scientific fields. With sensitive surface film as the sensitive element, AT-cut quartz crystal as energy transducer components by changes of the relationship between mass of surface film and frequency of QCM sensor transduces signals of mass or concentration into output frequency signal of sensor, thus achieve changes of mass or concentration detection. This paper mainly states how to design a low-cost QCM system platform with Arduino microcontroller board based on QCM sensor specific properties. For the oscillator circuit selection and differential frequency circuit design, the shield board has properly matched Arduino Mega2560, then by programming code to make Arduino acquire frequency of QCM sensor in real-time. Meanwhile, the interface and data store are corresponding convenient for real- time observing and data post-processing. By the tests of anhydrous ethanol evaporation, QCM system platform was calibrated and Sauerbrey equation verification. Moreover, this paper studies that photocatalytic degradation processing of Rhodamine B (RB) and methyl orange solution at the Surface of nanocrystalline TiO2 by QCM sensor.

Nos últimos anos, óxidos metálicos têm sido amplamente estudados para uma série de aplicações na indústria eletrônica e metalúrgica, sendo empregados em revestimentos anticorrosivos, sensores químicos, em dispositivos optoeletrônicos sensíveis, entre outros. Dentre os óxidos metálicos, o TiO2 (óxido de Titânio) tem enorme potencial em aplicações como sensor de gás, sensor de pH e em dispositivos fotossensíveis como células solares sensibilizadas por corante e para degradação fotocatalítica de compostos orgânicos. Há várias morfologias que podem ser obtidas para o TiO2, porém a de maior interesse atualmente é a de arranjos ordenados de nanotubos de TiO2 produzidos pelo processo de anodização do Ti, que por terem maior área superficial que outras morfologias como por exemplo, filmes finos, nanopilares e nanobastões, apresenta também maior sensibilidade à presença dos gases e/ou soluções a serem analisados, assim como maior absorção de fótons, além de uma menor recombinação de pares elétron-lacuna no material. Apesar destas várias vantagens, a atividade fotocatalítica do TiO2 é limitada por absorver apenas radiação ultravioleta devido a seu largo gap de aproximadamente 3,2 eV. Assim, neste trabalho foram produzidos nanotubos de TiO2 pelo processo de oxidação anódica do Ti, com diferentes parâmetros, correlacionando-os com a morfologia resultante. Com isso foi possível observar que o comprimento e diâmetro externo dos nanotubos de TiO2 crescem proporcionalmente com o aumento da tensão, sendo aproximadamente linear até um dado valor de saturação. A exceção a isto refere-se a nanotubos de TiO2 crescidos a partir de Ti depositado e substratos de vidro, no qual, há uma limitação de Ti a ser anodizado, de modo que após a conversão total do Ti em óxido não há mais o crescimento de nanotubos, porém os diâmetros gerados respeitam os mesmos valores para os casos em que não há essa limitação. Os nanotubos de TiO2 crescidos foram submetidos a processos de nitretação em um reator de deposição química a vapor assistida por plasma e os parâmetros foram avaliados com o intuito de encontrar as melhores condições para diminuição de seu gap, afim de aumentar sua atividade fotocatalítica. Pressão e potência de rádio frequência foram variados de 0,66 a 2,66 mBar (0,50 a 2,00 Torr) e 0,22 a 3,51 W/cm2 respectivamente. A maior diminuição no valor do gap, para 2,80 eV, foi obtida usando-se a pressão de 1,33 mBar (1,00 Torr), 1,75 W/cm2 de potência de rádio frequência durante um processo de 2 h a 320 °C, levando a uma diminuição de 14% no valor do gap e a um aumento de 25% na atividade fotocatalítica (redução de Azul de Metileno). Essa diminuição no valor do gap óptico dobra a abrangência de absorção de fótons de 5% para 10% do espectro solar. Os nanotubos de TiO2 nitretados produzidos com gap de 2,80 eV foram facilmente integrados a um microcanal de polidimetilsiloxano, produzindo um dispositivo fotocatalítico para estudo na fotodegradação de compostos orgânicos, podendo ser usado inclusive para redução de poluentes. O dispositivo fotocatalítico reduziu completamente 5 µL de solução de Azul de Metileno em cerca de 12 min, com uma taxa aproximadamente linear de 130 µM/h, enquanto os nanotubos de TiO2 como preparados apresentaram taxa de cerca de 115 µM/h. Logo, o dispositivo com nanotubos de TiO2 nitretados teve um aumento de 13% em sua eficiência de redução. / In recent years, metal oxides have been widely studied for a number of applications in the electronics and metallurgical industry, being used in anticorrosive coatings, chemical sensors, sensitive optoelectronic devices, among others. Among the metal oxides, TiO2 (titanium oxide) has enormous potential in applications such as gas sensor, pH sensor and in photosensitive devices such as dye sensitized solar cells and for photocatalytic degradation of organic compounds. There are several morphologies that can be obtained for TiO2, but the most interesting one today is ordered arrangements of TiO2 nanotubes produced by the Ti anodization process, which have a larger surface area than other morphologies such as thin films, nanopillars and nanobastones, also presents greater sensitivity to the presence of the gases and/or solutions to be analyzed, as well as greater absorption of photons, besides a smaller recombination of electron-hole pairs in the material. Despite these several advantages, the photocatalytic activity of TiO2 is limited by absorbing only ultraviolet radiation due to its wide gap of approximately 3.2 eV. Thus, in this work, TiO2 nanotubes were produced by the anodic oxidation process of Ti, with different parameters, correlating them with the resulting morphology. With this, it was possible to observe that the length and external diameter of the TiO2 nanotubes grow proportionally with the increase of the voltage, being approximately linear up to a given value of saturation. The exception to this relates to TiO2 nanotubes grown from Ti deposited and glass substrates, in which, there is a limitation of Ti to be anodized, so that after the total conversion of Ti to oxide, there is no longer growth of nanotubes, but the diameters generated respect the same values for cases in which there is no such limitation. The as grown TiO2 nanotubes were submitted to nitriding processes in a plasma assisted chemical vapor deposition reactor and the parameters were evaluated in order to find the best conditions to decrease their gap in order to increase their photocatalytic activity. Pressure and radio frequency power were varied from 0.66 to 2.66 mBar (0.50 to 2.00 Torr) and 0.22 to 3.51 W/cm2 respectively. The largest decrease in the gap value, to 2.80 eV, was obtained using the pressure of 1.33 mbar (1.00 Torr), 1.57 W/cm2 of radio frequency power during a process of 2 h in 320 °C, leading to a 14% decrease in gap value and a 25% increase in photocatalytic activity (reduction of Methylene Blue). This decrease in the value of the optical gap doubles the absorption range of photons from 5% to 10% of the solar spectrum. The nitrided TiO2 nanotubes produced with a gap of 2.80 eV were easily integrated into a microchannel of polydimethylsiloxane, producing a photocatalytic device for the study of photodegradation of organic compounds, and could be used to reduce pollutants. The photocatalytic device completely reduced 5 µL of Methylene Blue solution in about 12 min, with an approximately linear rate of 130 µM/h, whereas the TiO2 nanotubes as grown presented a rate of about 115 µM/h. Therefore, the device with nitrided TiO2 nanotubes had a 13% increase in its reduction efficiency.

This thesis focuses on the synthesis and characterisation of titanium dioxide (TiO2) thin films for photocatalytic applications and use in semi-transparent dye-sensitised solar cells for energy efficient glazing. Several synthetic methods for the production of TiO2 thin films are explored including sol-gel, aerosol-assisted chemical vapour deposition (CVD) and hybrid combinatorial CVD. For sol-gel processing two different precursors were studied; titanium tetra-isopropoxide (TTIP) and titanium bis-ammonium lactato dihydroxide (TiBALD). Non-ionic surfactants (Tween 20, 40, 60 and Brij 58 and 98) were successfully incorporated into all three methods for the production of TiO2 thin films modified morphology, microstructure and enhanced functional properties in some cases. All films are fully characterised using scanning electron microscopy, X-ray diffraction, atomic force microscopy, Raman spectroscopy, UV-Vis spectroscopy, contact angle analysis, as well as assessment for photocatalytic performance with resazurin 'intelligent' ink. Photocatalytic performance has been used as an indicator for performance in dye-sensitised solar cells (DSSCs). The best photocatalytic performances with half-lives of up to 2 minutes were obtained for thin films produced with the addition of Brij surfactants. A selection of thin films were tested in semi-transparent DSSC devices with up to 70% transparency, to determine their overall potential for use as energy-efficient glazing. Three DSSC device configurations were tested, whereby the optimum configuration used N3 "black" dye with a dye loading time of 42 hours in combination with a high performance iodine electrolyte and a platinum counter electrode. The highest power conversion efficiencies (PCE) obtained were within the region of 0.1 - 0.3 %, with the highest PCE of 0.3814 % obtained with a 3-layer TTIP sol-gel derived Brij 58 thin film (0.0006 mol dm3) which exhibited an short-circuit current of 0.857 mA/cm2, an open-circuit voltage of 0.71 V and a fill factor of 0.60.

With the increasing time people spend indoors, the indoor environment quality draws more and more attention. The concentration of indoor pollutants is usually much higher than outdoors, in which volatile organic compounds (VOCs) and mold/mildew are both major pollutants and cause many health problems to residents. Efforts devoted from academy and industry to protecting people from indoor environment problems are apparently not sufficient. Photocatalysts, such as TiO2, WO and ZnO, can absorb light photons and react with O2 and H2O to generate highly oxidative radicals, which can oxidize VOCs and disinfect microorganisms. Recently, this photocatalytic oxidation (PCO) technology has been intensively studied to reduce VOCs and disinfect bacteria in the indoor environment. Few papers address the indoor mold/mildew problem, and this research therefore endeavors to do so. The objectives are to evaluate the effectiveness of PCO technology to resist mold/mildew growth and prevent VOC emission from building materials under either UV or visible light irradiation. The models, including linear regression, logistic regression, and numerical model, are also built for interpreting experimental results and for predicting performance in application. The mold/mildew resistance of different PCO gels was examined using accelerated mold/mildew growth agar plate tests. These gels included TiO2 only and TiO2 in combination with H2O2 and with Ag. Without the application of PCO gels, no mold/mildew inhibition was observed from UV (365 nm) or visible light. Under UV light irradiation, the TiO2 gel achieved complete mold/mildew inhibition. Without light, a 12-day delay of mold growth was obtained using the Ag-TiO2/H2O2 gel. Under visible light irradiation, the Ag-TiO2/H2O2 gel was also the most effective PCO gel with a 8-day delay of mold growth, which, however, was shorter than the same gel in the condition of no light with a 10-day delay due to the light-induced deterioration of the Ag-TiO2. The reduction of VOC emission from PCO gel (TiO2 gel and Ag-TiO2/H2O2 gel) coated building materials under UV or visible light irradiation was also confirmed by small chamber tests (the Ag-TiO2/H2O2 gel with above 50% reduction of total VOC emission). A linear model was obtained for the Ag-TiO2/H2O2 gel in the condition of no light, with respect to the correlation between the delay of mold growth and the gel ingredients. A logistic model was created for predicting the probability of mold growth on different TiO2 gels with different UV light exposure time at different intensities. A numerical model was developed with better accuracy than the previous one for VOC emission from PCO gel coated building materials. This study showed that the PCO gel might be a promising multifunctional material in resisting mold/mildew growth and preventing VOC emission in the indoor environment (The TiO2 gel for complete mold/mildew inhibition and the Ag-TiO2/H2O2 gel for delay of mold growth in emergency situations and reduction of VOC emission from building materials). More stable Ag-TiO2 or other visible-light-driven photocatalysts are needed in future research because of the deterioration of the current one.

This study investigated the decomposition efficiency of acetone using unmodified (pure TiO2) and modified TiO2 (TiO2/ITO¡BTiO2/N) prepared by sputtering technology. The influence of operating parameters including wavelength and relative humidity on the decomposition efficiency of acetone was further discussed. Operating parameters investigated included light wavelength (350~400, 435~500, and 506~600 nm), photocatalysts (TiO2/ITO, TiO2/N, and TiO2), and relative humidity (RH) (0%, 50%, and 100%). In the experiments, acetone was degraded by photocatalysts in a self-designed batch photocatalytical reactor. Samples coated with TiO2 were placed in the batch reactor. The incident light with different wavelength was irradiated by a 20-watt lamp. Moreover, a low-pressure mercury lamp for UV light or LED lamps for blue and green lights were placed on the top of reactor. Acetone was injected into reactor by using a gasket syringe. Reactants and products were analyzed quantitatively by a gas chromatography with a flame ionization detector followed by a methaneizer (GC/FID-Methaneizer). The structure of the photocatalyst film surface showed taper and the width of column ranged from 100 to 200 nm. The film structure showed crystallization cylindrical surface and the thickness of the photocatalyst film was in the range of 4.0-4.3 £gm. The highest decomposition efficiency of acetone was observed by using TiO2/ITO under visible-light with 50% RH. The synthesis of TiO2 was mainly anatase for the tested photocatalysts. AFM images showed that the photocatalyst surface appeared rugged and the shape showed a mountain ridge distribution . Keywords: sputtering technology, modified photocatalysts, photosensitive, acetone, photocatalytic oxidation, acetone decomposition

Photocatalytic oxidation is an alternative water treatment method under consideration for disinfecting water. Chlorine disinfection can form harmful byproducts, and some viruses (e.g. adenoviruses) are resistant to other alternative disinfection methods. Photocatalytic oxidation using nano-sized photocatalytic particles (e.g. TiO2, fullerene) holds promise; however, it is limited by its low efficiency and long required treatment times. This research focuses on improving virus inactivation by photocatalytic oxidation by modifying catalysts for improved activity, by analyzing virus inactivation kinetics, and by elucidating the inactivation mechanisms of adenovirus serotype 2 (AdV2) and bacteriophage MS2. Modifying TiO2 with silver (nAg/TiO2) or silica (SiO2-TiO2) improves the inactivation kinetics of bacteriophage MS2 by a factor of 3-10. nAg/ TiO2 increases hydroxyl radical (HO•) production while SiO2 increases the adsorption of MS2 to TiO2. These results suggest that modifying the photocatalyst surface to increase contaminant adsorption is an important improvement strategy along with increasing HO• production. The inactivation kinetics of AdV2 by P25 TiO2 is much slower than the MS2 inactivation kinetics and displays a strong shoulder, which is not present in the MS2 kinetics. nAg/TiO2 initially improves the inactivation rate of AdV2. SiO2-TiO2 reduces the AdV2 inactivation kinetics since adsorption is not significantly enhanced, as it is with MS2. Amino-C60 is highly effective for AdV2 inactivation under visible light irradiation, making it a good material for use in solar disinfection systems. The efficacy of amino-fullerene also demonstrates that singlet oxygen is effective for AdV2 inactivation. When exposed to irradiated TiO2, AdV2 hexon proteins are heavily damaged resulting in the release of DNA. DNA damage is also present but may occur after capsids break. With MS2, the host interaction protein is rapidly damaged, but not the coat protein. The kinetics of MS2 inactivation are rapid since it may quickly lose its ability to attach to host cells, while AdV2 kinetics are slower since the entire capsid must undergo heavy oxidation before inactivation occurs. Adenovirus inactivation likely occurs through breaching the capsid followed by radical attack of DNA and core proteins.