Rozprawy doktorskie na temat „TiO2–CdS”

No presente trabalho, três tipos de fotocatalisadores híbridos nanométricos, CdS, CdS/TiO2, e CdS/TiO2/SiO2, foram preparados e utilizados em três aplicações fotoquímicas: fotodegradação macro e microscópica de um corante, fotólise da água para geração de H2 com acompanhamento via espectrometria de massas in situ e estudo de uma reação redox via microscopia de fluorescência de campo largo. As análises por microscopia eletrônica de varredura (MEV) e de transmissão (MET) apresentaram esferas de sílica com diâmetro em torno de 300 nm e nanopartículas de CdS e TiO2 com diâmetro da ordem de 5 nm e com alta aglomeração. O recobrimento da sílica com TiO2 e CdS não foi uniforme, resultando em \"ilhas\" preferencialmente isoladas. Apesar da morfologia heterogênea, os fotocatalisadores foram eficientes na degradação da safranina O, apresentando cinética de 1ª ordem em relação à concentração do corante. No que se refere à fotólise da água, o sistema ternário (CdS/TiO2/SiO2) apresentou a maior taxa de produção de H2 (0,79 mmol h-1 g-1), o que indica maior eficiência na transferência ou injeção de carga entre CdS e TiO2, devido ao melhor contato entre os dois semicondutores na superfície das nanopartículas (NPs) de sílica. Esse sistema também foi o mais eficiente na fotorredução do corante não fluorescente resazurina no corante fluorescente resorufina, acompanhada através de medidas de intermitência de fluorescência utilizando microscopia de fluorescência de campo largo. Em geral, os sistemas após adição do corante apresentaram intermitência de fluorescência mais lenta, com maiores tempos de relaxação de off. A fotorredução do corante estabeleceu um método interessante para o mapeamento das regiões de injeção de carga CdS/TiO2, inicialmente escuras e a seguir com alta intensidade de emissão.
In the present work, three types of nanosized hybrid photocatalysts, CdS, CdS/TiO2 and CdS/TiO2/SiO2, were synthesized and used in three photochemical applications: macro and microscopic photodegradation of a dye, photolysis of water to generate H2 monitored by in situ mass spectrometry and study of a redox reaction by wide-field fluorescence microscopy. Scanning (SEM) and transmission (TEM) electronic microscopies showed quasi-monodispersed silica spheres with a diameter of about 300 nm and CdS and TiO2 nanoparticles with a diameter of approximately 5 nm highly agglomerated. The coating of the silica with CdS and TiO2 was not uniform, resulting in \"islands\" preferentially isolated. Despite the heterogeneous morphology of the photocatalysts, they were efficient in the degradation of a safranine O solution, showing kinetics of first order with respect to dye concentration. With regard to water photolysis, the ternary system (CdS/TiO2/SiO2) showed the highest rate of H2 production (0.79 mmol g-1 h-1) , which indicates more efficient charge transfer or injection between CdS and TiO2 due to better contact between the two semiconductors on the surface of the silica nanoparticles (NPs). This system also was the most efficient photocatalyst in the photorreduction of the nonfluorescent dye resazurin into the fluorescent dye resorufin, monitored by fluorescence intermittency measurements using wide-field microscopy. In general, the systems after adding the dye presented slower fluorescence intermittency, with higher times of off relaxation. The photoreduction of the dye provided an interesting method for mapping the regions of CdS/TiO2 charge injection, initially dark and then with high emission intensity.

CoordenaÃÃo de AperfeiÃoamento de Pessoal de NÃvel Superior
Dedicado à deposiÃÃo e caracterizaÃÃo de filmes finos de Sulfeto de CÃdmio e DiÃxido de TitÃnio para a aplicaÃÃo em cÃlulas solares fotovoltaicas. Cada filme foi depositado por um processo diferente. O reagente TiO2 da marca vetec, foi misturado com Ãcido clorÃdrico em soluÃÃo aquosa formando uma dispersÃo. Essa dispersÃo foi espalhada sobre o substrato de vidro e depois aquecida com uma chapa aquecedora. Depois de formado o filme, foram feitos MEV e EDX do mesmo. Para preparar o CdS foi necessÃrio um procedimento um pouco mais complexo, que à a deposiÃÃo por banho quÃmico, onde à feita uma mistura de reagentes e mergulhado o substrato nesta mistura. Ocorreram reaÃÃes quÃmicas cujo resultado foi a formaÃÃo do CdS, que ocorre em toda a superfÃcie do recipiente e do substrato imerso na soluÃÃo. As mesmas caracterizaÃÃes feitas no TiO2 foram feitas no CdS, ambos mostraram uma boa uniformidade, tambÃm foi observado que os filmes mostraram uma boa aderÃncia ao substrato. A fim de comprovar a aplicatividade dos filmes para fins fotovoltaicos, preparou-se um protÃtipo de cÃlula solar fotovoltaica, que foi colocada em contato com a luz solar para assim medir a corrente elÃtrica e a diferenÃa de potencial. TambÃm foram medidos os mesmos parÃmetros no escuro, para comparaÃÃo de resultados e comprovaÃÃo da geraÃÃo de energia elÃtrica atravÃs do contato com a luz. AtravÃs dos resultados destes testes, concluiu-se que os filmes apresentaram o efeito fotoelÃtrico, sendo assim, aplicÃveis em cÃlulas solares fotovoltaicas.
This work is dedicated to the deposition and characterization of thin films of cadmium sulfide and titanium dioxide for application in photovoltaic solar cells. Each film is deposited by a different process. The reagent TiO2 brand Vetec, was mixed with hydrochloric acid in aqueous solution forming a dispersion. This dispersion is spread on the glass substrate and then heated with a plate heater. After the deposit, were made SEM and EDX of the films. In order to prepare CdS a more complex process called chemical bath deposition was required, made of a mixture of reagents with the substrate immersed in it. Chemical reactions occurred which result was the formation of CdS, which occurs across the surface of the container and the substrate immersed in the solution. The same characterizations were carried out on TiO2 in CdS, showed in both good uniformity, was also observed that the films showed good adhesion to the substrate. In order to prove that films are applicable for photovoltaic energy conversion, a prototype of a solar photovoltaic cell was prepared, which was placed in contact with a type of light for measuring electrical parameters like the electric current and potential difference. We also measured the same parameters in the dark, for comparison of results and to prove power generation in contact with the light. The research tests provides evidence that films showed the photoelectric effect, therefore, applicable in photovoltaic solar cells.

De nombreuses incertitudes persistent sur la toxicité potentielle des nanoparticules (NPs) et leur devenir dans l’organisme humain. L’objectif de ce travail est de mieux comprendre les mécanismes cytotoxiques induits par des NPs métalliques sur une cible secondaire, représentée par le rein. En effet, les NPs sont susceptibles de franchir les barrières cellulaires, d’être véhiculées par le sang pour se retrouver filtrées par le rein au niveau des cellules glomérulaires et peut-être, réabsorbées au niveau des cellules tubulaires. Cette étude est réalisée in vitro, avec des NPs métalliques de titane (TiO2 : 12 nm), de zinc (ZnO : 75 nm) et de cadmium (CdS : 8 nm), sur cellules mésangiales (IP15) et cellules épithéliales tubulaires (HK-2). Les résultats démontrent des effets variables selon le type cellulaire étudié, la nature chimique des NPs et leur solubilité. Si les NPs insolubles de TiO2 (CI50>100 µg/cm²) ne sont que très peu toxiques, les NPs de CdS et de ZnO le sont bien plus du fait de leur solubilité (CI50<7 µg/cm²). La libération de cations métalliques Cd2+ et Zn2+ est à l’origine de cette toxicité. La production d’ERO et la perturbation du statut oxydatif cellulaire (GSH/GSSG) sont corrélées aux effets cytotoxiques des NPs de ZnO et CdS. Une approche moléculaire permet d’identifier les voies de signalisation cellulaire intervenant dans la réponse au stress (translocation nucléaire des facteurs de transcription : Nrf2 et NF-κB). L’internalisation et l’accumulation, des NPs de TiO2 et de CdS, sont responsables de l’induction d’un stress oxydant et d’un effet cytotoxique lors d’exposition sur le long terme
Many uncertainties remain about the potential toxic effect of nanoparticles (NPs), and their becoming in human organism. The aim of this study was to understand the cytotoxic mechanisms induced by metallic NPs, on a secondary target organ, the kidney. NPs were able to cross biological barriers, be carried in blood to kidney cells, on glomerular or tubular cells. This study was performed in vitro, with NPs of titanium (TiO2: 12 nm), zinc (ZnO: 75 nm) and cadmium (CdS: 8 nm), on mesangial IP-15 cells and epithelial HK-2 cells. Results showed effects depending on cell type, chemical nature of NPs and their solubility. TiO2 NPs have no cytotoxic effect (IC50>100µg/cm²), probably due to their insolubility. Exposure to CdS and ZnO NPs lead to cell death (IC50< 7 µg/ cm²). Release of metallic cations Cd2+ and Zn2+ are the main causes of toxicity. ROS production and disruption of oxidative cellular balance (GSH/ GSSG) were correlated to the cytotoxic effects of ZnO and CdS NPs. A molecular approach was used to identify signaling pathways involved in oxidative stress response (nuclear translocation of NF-kappaB and Nrf2).Internalization and accumulation of TiO2 and CdS NPs were responsible of oxidative stress induction and cytotoxic effect on long term exposure

SOUSA, C. B. A. Obtenção e análise de filmes finos de CdS e TiO2 para uso em células solares fotovoltaicas. 2010. 85 f. Dissertação (Mestrado em Engenharia Mecânica) – Centro de Tecnologia, Universidade Federal do Ceará, Fortaleza, 2010.
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This work is dedicated to the deposition and characterization of thin films of cadmium sulfide and titanium dioxide for application in photovoltaic solar cells. Each film is deposited by a different process. The reagent TiO2 brand Vetec, was mixed with hydrochloric acid in aqueous solution forming a dispersion. This dispersion is spread on the glass substrate and then heated with a plate heater. After the deposit, were made SEM and EDX of the films. In order to prepare CdS a more complex process called chemical bath deposition was required, made of a mixture of reagents with the substrate immersed in it. Chemical reactions occurred which result was the formation of CdS, which occurs across the surface of the container and the substrate immersed in the solution. The same characterizations were carried out on TiO2 in CdS, showed in both good uniformity, was also observed that the films showed good adhesion to the substrate. In order to prove that films are applicable for photovoltaic energy conversion, a prototype of a solar photovoltaic cell was prepared, which was placed in contact with a type of light for measuring electrical parameters like the electric current and potential difference. We also measured the same parameters in the dark, for comparison of results and to prove power generation in contact with the light. The research tests provides evidence that films showed the photoelectric effect, therefore, applicable in photovoltaic solar cells.
Dedicado à deposição e caracterização de filmes finos de Sulfeto de Cádmio e Dióxido de Titânio para a aplicação em células solares fotovoltaicas. Cada filme foi depositado por um processo diferente. O reagente TiO2 da marca vetec, foi misturado com ácido clorídrico em solução aquosa formando uma dispersão. Essa dispersão foi espalhada sobre o substrato de vidro e depois aquecida com uma chapa aquecedora. Depois de formado o filme, foram feitos MEV e EDX do mesmo. Para preparar o CdS foi necessário um procedimento um pouco mais complexo, que é a deposição por banho químico, onde é feita uma mistura de reagentes e mergulhado o substrato nesta mistura. Ocorreram reações químicas cujo resultado foi a formação do CdS, que ocorre em toda a superfície do recipiente e do substrato imerso na solução. As mesmas caracterizações feitas no TiO2 foram feitas no CdS, ambos mostraram uma boa uniformidade, também foi observado que os filmes mostraram uma boa aderência ao substrato. A fim de comprovar a aplicatividade dos filmes para fins fotovoltaicos, preparou-se um protótipo de célula solar fotovoltaica, que foi colocada em contato com a luz solar para assim medir a corrente elétrica e a diferença de potencial. Também foram medidos os mesmos parâmetros no escuro, para comparação de resultados e comprovação da geração de energia elétrica através do contato com a luz. Através dos resultados destes testes, concluiu-se que os filmes apresentaram o efeito fotoelétrico, sendo assim, aplicáveis em células solares fotovoltaicas.

CoordenaÃÃo de AperfeÃoamento de Pessoal de NÃvel Superior
This research describes the process of obtaining a photovoltaic cell, since getting electrical conductor glasses used for the flow of electrons coming from the photovoltaic effect until the deposition of thin films of semiconductor titanium dioxide (TiO2) and cadmium sulfide (CdS) at each of these glasses. The use of natural or synthetic dyes deposited on titanium dioxide layer has the objective to increase the absorption spectrum of the TiO2, since sunlight emits most of its energy in the frequency range of visible light. After joining the two glasses with thin films deposited over TiO2 plus dye and CdS, it was used a potassium triiodide electrolyte for regeneration and consequently the activation of photovoltaic solar cell. After mounting the cell concerned, tests of photoactivity have been performed by exposing the cells to sunlight collected for specified periods and the values of voltage and photocurrent generated. Theoretical studies have been conducted to mathematical modeling of the behavior of the solar cell mounted, and then we have analyzed the efficiency of converting solar energy into electrical energy. The constituents of the cell have been characterized by the techniques of X-ray diffraction (XRD) and scanning electron microscopy (SEM) for analyzing the porosity, uniformity and other physical parameters of thin films.
O presente trabalho descreve o processo de obtenÃÃo de uma cÃlula fotovoltaica, desde a obtenÃÃo de vidros condutores elÃtricos utilizados para o fluxo dos elÃtrons oriundos do efeito fotovoltaico, atà a deposiÃÃo dos filmes finos dos semicondutores diÃxido de titÃnio (TiO2) e sulfeto de cÃdmio (CdS) em cada um dos vidros. O uso de corantes naturais ou sintÃticos na camada depositada de diÃxido de titÃnio possuiu como objetivo aumentar o espectro de absorÃÃo do mesmo, uma vez que a luz solar emite uma grande parte de sua energia na faixa de frequÃncia da luz visÃvel. Depois de unir os dois vidros com os filmes finos depositados de TiO2 mais corante e o CdS, utilizou-se o eletrÃlito de tri-iodeto de potÃssio para a regeneraÃÃo e consequentemente a ativaÃÃo da cÃlula solar fotovoltaica. ApÃs a montagem da cÃlula em questÃo, foram realizados testes de fotoatividade, expondo as cÃlulas ao sol por perÃodos determinados e coletados os valores da fotocorrente gerada e a tensÃo, alÃm disso, foram realizados estudos teÃricos para modelagem matemÃtica do comportamento da cÃlula solar montada e em seguida analisou-se a eficiÃncia de conversÃo de energia solar em energia elÃtrica. Os constituintes da cÃlula foram caracterizados pelas tÃcnicas de difraÃÃo de raios-X (DRX) e microscopia eletrÃnica de varredura (MEV) para analisar a porosidade, uniformidade e outros parÃmetros fÃsicos dos filmes finos.

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CNPq
No presente trabalho foi investigado o desempenho de nanotubos de TiO2 sensibilizados com quantum dots de CdS na geração de hidrogênio por meio da reação de dissociação da água por meio da fotocatálise e fotoeletrocatálise. Os nanotubos de TiO2 foram obtidos pelo método de anodização (30 V, 1 hora) de chapas de Ti, em etilenoglicol e água contendo íons fluoreto. As amostras anodizadas foram submetidas a tratamento térmico 400°C durante 3 horas. Posteriormente as amostras foram sensibilizadas com quantum dots de CdS via síntese hidrotérmica in situ usando o ácido 3-mercaptopropiônico como agente estabilizante. A eficiência fotocatalítica dos materiais na produção de hidrogênio foi investigada por meio da reação de dissociação da água utilizando como fonte de irradiação um simulador solar. A quantificação do hidrogênio gerado foi determinada por meio de cromatógrafia gasosa. Por outro lado, para estimar a eficiência de geração de hidrogênio via fotoeletrocatálise, as amostras foram avaliadas como fotoânodos e medidas da fotocorrente gerada pela irradiação em uma célula fotoeletroquímica (PEC) de três eletrodos foram realizadas. A sensibilização dos nanotubos de TiO2 com os quantum dots de CdS a partir da síntese hidrotérmica in situ, permitiu uma boa impregnação e distribuição uniforme dos quantum dots ao redor da superfície dos nanotubos, de acordo com as análises de EDS e XPS. O perfil de profundidade de XPS mostrou que a concentração de CdS permaneceu praticamente inalterada (homogênea) ao longo da matriz nanotubular. A presença de ânions sulfato evidenciou a oxidação do material preferentemente na superfície. Os nanotubos conferem uma proteção ao CdS frente à oxidação e protegem também os quantum dots quanto à fotocorrosão na solução de sacrifício S2-/SO32- utilizada. Este comportamento define uma boa estabilidade na fotocorrente gerada como mostrado em experimentos de longa duração (20 horas) sob irradiação. Os resultados experimentais mostraram três comportamentos diferentes para a geração de H2 quando o tempo de síntese dos QDs de CdS aumenta. Foram observados, efeitos similares, antagônicos e sinérgicos frente à atividade fotocatalítica em relação aos nanotubos de TiO2. O efeito antagônico parece estar relacionado com a presença de duas populações de tamanhos de QDs de CdS, onde a população com um band gap menor atua como uma armadilha para os elétrons fotogerados pela população com um band gap maior, diminuindo a atividade fotocatalítica do TiO2 na região ultravioleta. A transferência de elétrons a partir dos QDs de CdS para o TiO2 foi comprovada pelos resultados de UPS combinados com as medidas do band gap óptico. A maior absorção no visível após a sensibilização com o CdS combinada com a transferência de elétrons possibilita um incremento na taxa de geração de hidrogênio por meio da fotocatálise a partir de luz visível de quase zero para os nanotubos de TiO2 até cerca de 0,3 μmol cm-2 h-1 após sensibilização com os QDs de CdS. No caso da fotoeletrocatálise em uma PEC, a taxa de geração de H2 a partir de luz visível estimada pela fotocorrente gerada após a sensibilização (1,79 μmol cm-2 h-1) chega a ser até 12 vezes maior que para os nanotubos de TiO2 sem sensibilizar (0,15 μmol cm-2 h-1).
In the present work, we investigated the performance of TiO2 nanotubes sensitized with CdS quantum dots on the photocatalytic and photoelectrocatalytic H2 production reaction. TiO2 nanotubes were obtained by anodization of Ti foil, followed by annealing to crystallize the nanotubes into anatase phase. Afterwards, the samples were sensitized with CdS quantum dots via an in situ hydrothermal route using 3-mercaptopropionic acid as the capping agent. This sensitization technique permits high loading and uniform distribution of CdS quantum dots onto TiO2 nanotubes. The XPS depth profile showed that CdS concentration remains almost unchanged (homogenous), while the concentration relative to the sulfate anion decreases by more than 80 % with respect to the initial value after ~200 nm in depth. The presence of sulfate anions is due to the oxidation of sulfide and occurs in greater proportion in the material surface. This protection for air oxidation inside the nanotubular matrix also protected the CdS from photocorrosion in sacrificial solution leading to good stability properties proved by a long duration photocurrent measurements. The effect of the sizes of CdS quantum dots attached to TiO2 nanotubes on the hydrogen production via photocatalysis was investigated. The experimental results showed three different behaviors when the CdS size is increased in the sensitized samples, e.g., similar, deactivation and activation effects on the hydrogen production with regard to TiO2 nanotubes. The deactivation effect was related with two populations of sizes of CdS, where the population with a shorter band gap acts as a trap for the electrons photogenerated by the population with a larger band gap. Electron transfer from CdS quantum dots to TiO2 semiconductor nanotubes was proven by the results of UPS combined with optical band gap measurements. This property facilitates an improvement of the visible-light photocatalytic hydrogen evolution rate from zero, for TiO2 nanotubes, to approximately 0.3 μmolcm-2h-1 for TiO2 nanotubes sensitized with CdS quantum dots. The hydrogen generation rate estimated from photocurrents measurements via photoelectrocatalysis in PEC systems was also investigated. The hydrogen generation rate after sensitization was improved from 0,15 μmol cm-2 h-1 to 1,79 μmol cm-2 h-1, near to 12 times better performance under visible-light irradiation.

MELO, T. F. Obtenção de uma célula solar fotovoltaica baseada em CdS e TiO2 fotossensibilizada com corante em substrato de vidro com camada condutora. 2014. 90 f. Dissertação (Mestrado em Engenharia Mecânica) – Centro de Tecnologia, Universidade Federal do Ceará, Fortaleza, 2014.
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This research describes the process of obtaining a photovoltaic cell, since getting electrical conductor glasses used for the flow of electrons coming from the photovoltaic effect until the deposition of thin films of semiconductor titanium dioxide (TiO2) and cadmium sulfide (CdS) at each of these glasses. The use of natural or synthetic dyes deposited on titanium dioxide layer has the objective to increase the absorption spectrum of the TiO2, since sunlight emits most of its energy in the frequency range of visible light. After joining the two glasses with thin films deposited over TiO2 plus dye and CdS, it was used a potassium triiodide electrolyte for regeneration and consequently the activation of photovoltaic solar cell. After mounting the cell concerned, tests of photoactivity have been performed by exposing the cells to sunlight collected for specified periods and the values of voltage and photocurrent generated. Theoretical studies have been conducted to mathematical modeling of the behavior of the solar cell mounted, and then we have analyzed the efficiency of converting solar energy into electrical energy. The constituents of the cell have been characterized by the techniques of X-ray diffraction (XRD) and scanning electron microscopy (SEM) for analyzing the porosity, uniformity and other physical parameters of thin films.
O presente trabalho descreve o processo de obtenção de uma célula fotovoltaica, desde a obtenção de vidros condutores elétricos utilizados para o fluxo dos elétrons oriundos do efeito fotovoltaico, até a deposição dos filmes finos dos semicondutores dióxido de titânio (TiO2) e sulfeto de cádmio (CdS) em cada um dos vidros. O uso de corantes naturais ou sintéticos na camada depositada de dióxido de titânio possuiu como objetivo aumentar o espectro de absorção do mesmo, uma vez que a luz solar emite uma grande parte de sua energia na faixa de frequência da luz visível. Depois de unir os dois vidros com os filmes finos depositados de TiO2 mais corante e o CdS, utilizou-se o eletrólito de tri-iodeto de potássio para a regeneração e consequentemente a ativação da célula solar fotovoltaica. Após a montagem da célula em questão, foram realizados testes de fotoatividade, expondo as células ao sol por períodos determinados e coletados os valores da fotocorrente gerada e a tensão, além disso, foram realizados estudos teóricos para modelagem matemática do comportamento da célula solar montada e em seguida analisou-se a eficiência de conversão de energia solar em energia elétrica. Os constituintes da célula foram caracterizados pelas técnicas de difração de raios-X (DRX) e microscopia eletrônica de varredura (MEV) para analisar a porosidade, uniformidade e outros parâmetros físicos dos filmes finos.

Abstract The present Thesis discusses various Titanium dioxide (TiO2) - Cadmium Sulfide (CdS) assemblies for efficient harvesting of the solar photon. Inorganic semiconductor nanocrystals such as CdS have attracted considerable attention in the realm of solar photon harvesting mainly due to beneficial properties such as easy tunability of their optical, electrical, magnetic properties, functional stability i.e. non-degradability under atmospheric conditions, materials synthesis and device fabrication by benchtop methods. However, a major detrimental issue that prevails in semiconductor nanocrystals is charge recombination. Tailored semiconductor assemblies with favourable energetics can significantly alleviate the effect of charge recombination. Improved charge separation in an optimum semiconductor assembly may aid in decrease in charge recombination and hence, result in enhanced photoelectrochemical function. Owing to the band structure, CdS can harvest solar photon and when attached with wide band gap semiconductor TiO2. The photogenerated electron in the CdS conduction band can be injected at ultrafast timescales to the conduction band of the TiO2. The thesis discusses easy and cost-effective synthesis of various TiO2 and CdS assemblies and explores application of them in photovoltaics, photocatalysis and (photo conducting) image sensor. Various interactions and physical properties are also studied including the ultrafast photoinduced electron dynamics from CdS to TiO2. Sun is a great source of alternative energy especially, electrical energy. In this context, nanostructured semiconductor assemblies have demonstrated great potential towards efficient harvest of the solar photon. In Chapter 1, general properties and scope of nanostructured assemblies in the context of few applications namely liquid junction semiconductor sensitized solar cell (for solar photon conversion to electricity), visible light photocatalysis (to degrade pollutants using solar photon) and large area image sensor (sensitive to white light) are discussed. The Chapter also discusses the various characterization and quantification methods which not only provide detailed analysis of properties of the novel semiconductor assemblies but also throw light on the prospects for industrial applications. Chapters 2 to 5 comprises of discussions on the electronic and photovoltaic properties of various shaped semiconductor nanocrystals (average size  30 nm). In Chapter 2, cadmium sulfide (CdS) semiconductor nanocrystals of various shapes (tetrapod, tetrahedron, sphere and rod) obtained using an optimized solvothermal process exhibited a mixed cubic (zinc blende) and hexagonal (wurtzite) crystal structure. The various nanocrystal shapes obtained here are a consequence of the simultaneous presence of wurtzite and zinc blende phases in varying amounts. The simultaneous presence of the two crystal phases in varying amounts is observed to play a pivotal role in not only determining the final nanocrystal shape but also both the electronic and photovoltaic properties of the CdS nanocrystals. Light to electrical energy conversion efficiencies measured in two-electrode configuration laboratory solar cells remarkably decreased by one order in magnitude from tetrapod  tetrahedron  sphere  rod. The tetrapod-CdS nanocrystals, which displayed the highest light to electrical energy conversion efficiency, showed a favourable shift in position of the conduction band edge leading to highest rate of electron injection (from CdS to TiO2) and lowest rate of electron-hole recombination (higher free electron lifetimes). Chapter 2 successfully demonstrated that the photovoltaic (PV) efficiency of a device can be influenced by tuning the shape of the light harvester nanocrystal. While the light to electricity conversion efficiencies varied by one order in magnitude between the various nanocrystal shapes (average size  30 nm), the magnitude of the efficiencies was itself not very high. In Chapter 3, the same nanocrystal shapes are used to sensitize multi-layered Titania films and liquid junction solar cells are then fabricated using them. This optimization of the cell configuration showed tremendous enhancement in the light to electricity conversion efficiency by nearly one order in magnitude compared to the ones discussed in Chapter 2. The semiconductor-electrolyte interface is also studied in detail by performing ac-impedance spectroscopy on the full cell to estimate the electron lifetime of the device. The estimated recombination resistance and the electron lifetime are observed to follow the same trend as of the PV-performances of the cells composed of various shaped nanocrystals in the new configuration. The photoinduced electron transfer processes in a nano-heterostructure semiconductor assembly are complex and depend on various parameters of the constituents of the assembly. Chapter 4 discusses the ultrafast electron transfer characteristics of an assembly comprising of a wide band gap semiconductor, titanium dioxide (TiO2) attached to light harvesting cadmium sulfide (CdS) nanocrystals of varying crystallographic phase content. The nanocrystals employed here are the same as that discussed in Chapters 2 and 3. Quantitative analysis of synchrotron high resolution X-ray diffraction data of CdS nanocrystals precisely reveal the presence of both wurtzite and zinc blende phases in varying amounts. The biphasic nature of CdS influences directly the shape of the nanocrystal at long reaction times (as also highlighted in Chapters 2 and 3) as well as the transfer of the photo-excited electrons from the CdS to TiO2 as obtained from transient absorption spectroscopy. Higher amount of zinc blende phase is observed to be beneficial for fast electron transfer across the CdS-TiO2 interface. The electron transfer rate constant differs by one order in magnitude between the CdS nanocrystals and varies linearly with the fraction of the phases. Chapters 2-4 show that the electron recombination lifetime in a sensitized semiconductor assembly, which has a major impact on the performance in a solar cell, is greatly influenced by the crystal structure and geometric form of the light harvesting semiconductor nanocrystal. In Chapter 5, the final Thesis Chapter related to semiconductor assemblies for liquid junction based semiconductor sensitized solar cells, deals with the influence of downsizing of light harvester nanocrystals on the electron recombination lifetime and its eventual influence on the light to electricity conversion efficiency of the solar cell. The semiconductor (photoanode)-electrolyte interface in a liquid junction semiconductor sensitized solar cell which has a direct impact on the photovoltaic performance is probed here systematically. The light harvesting cadmium sulfide (CdS) nanocrystals (average size  6-12 nm) of distinctly different and controlled shapes are obtained using a novel and simple liquid-gas phase synthesis method performed at different temperatures involving very short reaction times. High resolution synchrotron X-ray diffraction and spectroscopic studies respectively exhibit different crystallographic phase content and optical properties. When assembled on a mesoscopic TiO2 film by a linker molecule, they exhibit remarkable variation in electron recombination lifetime by one order in magnitude, as determined by ac-impedance spectroscopy. This also drastically affects the photovoltaic efficiency of the differently shaped nanocrystals sensitized solar cells. In Chapter 6, focus shifts from liquid junction semiconductor sensitized solar cells to visible light photocatalysis. The possibility of harvesting light via a semiconductor assembly of the same chemical compositions (as in Chapters 2-5) however, in a different spatial configuration is again explored. An unprecedented morphology of titanium dioxide (TiO2) and cadmium sulfide (CdS) self-assembly obtained using a ‘truly’ one-pot and highly cost-effective method with a multi-gram scale yield is discussed here. The TiO2– CdS assembly comprised of TiO2 and CdS nanoparticles residing next to each other homogeneously self-assemble into ‘woollen knitting ball’ like microspheres. The microspheres exhibited remarkable potential as a visible light photocatalysts with high recyclability. Finally, in Chapter 7, a semiconductors assembly comprising of titanium dioxide (TiO2) rods sensitized by cadmium sulfide (CdS) nanocrystals for potential applications in large area electronics on three dimensional (3-D) substrates is discussed. Vertically aligned TiO2 rods are grown on a substrate using a 1500C process flow and then sensitized with CdS by SILAR method at room temperature. This structure forms an effective photoconductor as the photo-generated electrons are rapidly removed from the CdS (‘carpet’) via the TiO2 thereby permitting a hole rich CdS. Current-voltage characteristics are measured, and models illustrate space charge limited photo-current as the mechanism of charge transport at moderate voltage bias. With this stable assembly, high speed can be achieved. The frequency response with a loading of 10 pF and 9 M shows a half power frequency of 100 Hz.

碩士
國立中正大學
光機電整合工程研究所
105
Graphene is a suitable material in the application of photodetectors due to its excellent physical properties. However, it has the disadvantage of a weaker photoresponse. In this study, the photoresponse of graphene is enhanced through the spin coating of titanium dioxide (TiO2). Although TiO2 have superior photoresponse performance in ultraviolet region, due to the limit of its energy gap, there is almost no photoresponse in visible light region. In this study, we produce graphene composite device by growing cadmium sulfide (CdS) through Successive Ionic Layer Adsorption and Reaction (SILAR) method. Utilizing the absorption of CdS in visible light region, we are able to enhance the photorepsonse of the grapheme composite device in both ultraviolet and visible light region. In this study, we fabricated and measured the optoelectronic properties of both CdS/G and CdS/TiO2/G composite device. The results show that CdS/TiO2/G composite device have the best photoresponse performance under 365 nm LED light source. Thus, we measure the device’s properties under different voltage and optical intensity. We also measure the full spectral response of CdS/TiO2/G composite device under Xenon light source. We discover that the device have great photoresponse performance under wavelength from 300 nm to 600 nm, over 100A/W in 300 nm to 500 nm region with the best value of 889.2 A/W under 300 nm. This prove that utilizing CdS and TiO2, we are able to significantly increase the photoreponse of graphene devices.

碩士
國立成功大學
化學工程學系碩博士班
97
These studies utilize the method of chemical bath deposition (CBD) to assemble, CdS and CdSe onto porous TiO2 films as sensitizer for photoelectrochemical hydrogen generation. The sensitizer incorporated amount and co-sensitized effect on photoelectrochemical conversion efficiency were discussed in this study. The results show that the CdS/CdSe co-sensitized photoelectrode has not only a complementary effect in light harvest and the cascade structure, TiO2/CdS(4)/CdSe(4), but leads to a stepwise structure of band-edge levels which is advantageous to the electron injection and hole-recovery of the system. The energy conversion efficiency (ECE) achieved by the TiO2/CdS(4)/CdSe(4) electrode under illumination (AM1.5, UV cut-off, 100 mW/cm2) is 7.4%. Zinc Sulfide (ZnS) was further deposited as passivation layer to improve the photoelectrode stability and reduce leakage current. The corresponding hydrogen evolved rate measured for the TiO2/CdS(4)/ CdSe(4)/ZnS electrode is 210 µmol．cm-2．h-1. Further, thermal-treatment process was used to improve TiO2/sensitizer interface and increase sensitizer crystallinity, the electron transfer ability of photoelectrodes and decrease the electrode defects. At the temperature of 300℃ and 150℃, the electrode TiO2/CdS(4)300℃/CdSe(4)150℃ had the highest photocurrent density about 17 mA/cm2 and ECE is 10.6%.

碩士
中原大學
化學研究所
102
Titanium oxide nanotube arrays (TNA) were fabricated from titanium foil by anodizing process. TNA was a good photocatalytic material because of its high surface area and continuous electron transfer path. This study focus on the materials of TNA, and modifications such as CdS modified TNA. The photochemical catalysis of water splitting experiments using above materials for hydrogen generation were investigated. CdS sensitized TiO2 nanotube arrays (TNA) was fabricated by inserting CdS nanoparticles into TNA via ultrasonic-assisted chemical bath deposition, and its effect on photocatalytic properties and hydrogen generation rate were discussed in this study. To enhance the optical response of TNA, TNA will be immersed in Cd2 + and S2-containing solution, 5,10,15,20 cycle times, CdS modified TNA was formed by the immersion method. When soaking in higher number of times, the surface color of TNA changed from light yellow to dark yellow. Immersion of TNA for 15 times in CdS solution generated 1.462 mA/cm2 photocurrent, compared to 0.075 mA/cm2 of TNA-pure increase of 21.9 times was obtained.

碩士
國立成功大學
化學工程學系碩博士班
98
In this study, the CdS/TiO2 photoanodes were prepared by chemical bath deposition (CBD) technique. The photoactivity of CdS/TiO2 photoanodes and hydrogen generation were studied via photoelectrochemical (PEC) process. Experimentally, the self-assembled TiO2 nanotube arrays were formed by electrochemical anodization process, then the TiO2 nanotubes arrays were sequentially immersed in Cd(NO3)2 and Na2S solution several times to fabricate CdS/TiO2 photoanode. The experimental conditions including calcination atmosphere and temperature, immersion time, number of immersion, solvent, and UV illumination were investigated. Besides, the properties of CdS/TiO2 photoanodes such as surface morphology, crystalline structure and band gap were discussed. The photoactivities of CdS/TiO2 photoanodes and hydrogen generation via photoelectrochemical splitting of water were also studied. From the experimental results, the photoactivity of photoanode calcined in air atmosphere was better than that in nitrogen atmosphere. The CdS grains calcined at 300 oC was zinc blende structure with small quantity of wurtzite. From the PEC results, it revealed that the CdS/TiO2 sample with the highest photoactivity was obtained at immersing time of 20min and repeating 13 cycles. The saturation current density was 6.163 mA/cm2 and the maximum photoelectrochemical conversion was 4.45 % in the PEC system under Xenon lamp (I0 = 100 mW/cm2) illumination. The hydrogen generation rate for the sample was 1.49 ml/cm2-hr measured with a double-tank PEC reactor. The solvent effect in CBD procedure was investigated in advance. It was found that the photoactivities of CdS(W)/TiO2 prepared starting from the aqueous Cd(NO3)2 solution were higher than those of prepared in ethanol(95%) solution. From the result of characterization, as compared with CdS(A)/TiO2, the CdS(W)/TiO2 showed bigger particle size. However, the CdS amount in CdS(W)/TiO2 sample was relatively large, and the band gap was smaller. On the other hand, the photoactivity of CdS(UV)/TiO2 which prepared under UV (λmax=253.7 nm) illumination somewhat reduced. In the presence of UV light, it resulted in increase of the Cd2+ adsorption on the TiO2 surface. However, it also accompanied with aggregation of CdS.

碩士
國立成功大學
化學工程學系碩博士班
100
In this work, ZnS/CdS/TiO2 photoanodes were prepared by pulse electrodeposition from zinc chloride and sodium thiosulfate solutions. The influence of the electrodeposition condition on the composition and structure of photoanode was investgated. Furthermore, the photoelectrochemical activities and hydrogen production rates of the photoanodes were also studied. For the study of ZnS electrodeposition, the preparation conditions including applied voltage, electrolyte composition, pH, input electricity, deposition temperature, and calcination temperature were investigated. The characterizations of photoanodes were investigated by means of XRD, SEM, TEM, XPS and UV techniques. In order to measure the photoactivity of prepared photoanode, a photoelectrochemical (PEC) cell with an electrolyte of 0.25 M Na2S and 0.35 M Na2SO3 were used under illumination by Xe lamp (100 mW/cm2). Moreover, the hydrogen generation experiment was carried out in a two-compartment PEC reactor. The concentration of alkaline electrolyte and the stirring rate in the anode compartment were investigated as well. The results showed that deposition amount, particle size, defects, and surface charges of ZnS layer were strongly influenced by the deposition conditions, which would in advance manipulate the photoactivity of photoanode. It was found that the optimal deposition conditions were: reductive voltage of -0.8 V (vs. Ag/AgCl), the electrolyte of 0.03 M ZnCl2, 0.3 M Na2S2O3, pH3, input reductive electricity of 1 C, deposition temperature of 25 ℃ and calcination temperature of 300 ℃. From the results of hydrogen genetation experiment, it revealed that the hydrogen generation condition was optimized at rotating speed of 300 rpm and the electrolyte of 1 M NaOH, 0.35 M Na2SO3 and 0.25 M Na2S. When the ZnS/CdS/TiO2 photoanode equipped with the PEC cell were operated at the optimal conditions, a maximum photocurrent density (8.17 mA/cm2) and photoconversion efficiency (3.56%) could be achieved. Moreover, the hydrogen generation rate reached to 87.98 mol/cm2-h with a long-term stability. As compared with CdS/TiO2 photoanode, the studied ZnS/CdS/TiO2 photoanode exhibited not only a promotion in photoactivity but also an increase in the hydrogen production rate. The lifetime of photoanode was increased as well, owing to the reduction in photocorrosion of photoanode.

碩士
國立中興大學
奈米科學研究所
105
In this study, titanium dioxide particles using different pH values ranging from 3 to 11 are prepared by sol-gel method, while, cadmium sulfide quantum dots with size about 5nm are synthesized by reverse micelles method. The photoelectrode paste of the quantum dot-sensitized solar cells are prepared by mixing of different ratio of TiO2 and CdS. The solar cell using the photoelectrode paste that is prepared with pH = 7 and TiO2/CdS=1 has the best performance. The photoelectric conversion efficiency of this cell is 0.8, and the short circuit current density is 2.47mA/cm2,, and the open circuit voltage equals to 0.68V. Ac impedance is employed to investigate the electron transport mechanism between the interfaces of the battery.

碩士
逢甲大學
材料與製造工程所
94
A study on the synthesis and their photocatalytic activities of TiO2 hollow spheres and composite CdS/TiO2 hollow spheres was discussed in this research. Polystyrene (PS) nanoparticles, used as a template, were prepared by emulsion-free polymerization using AIBA as an initiator. With these PS nanoparticles and titanium tetraisopropoxide (TTIP) precursor, PS/TiO2 core-shell composite spheres were prepared. After removing PS by calcination under different temperatures, different kinds of crystalline morphology of TiO2 hollow spheres were then obtained. To prepare composite CdS/TiO2 hollow spheres, the as-prepared TiO2 hollow spheres were further doped with CdS. Comparison of the photocatalytic activities between TiO2 hollow spheres and composite CdS/TiO2 hollow spheres were discussed extensively in the whole study.

碩士
國立臺灣大學
環境工程學研究所
102
Hydrogen gas is one of the most promising renewable energy nowadays as it has high energy yield and zero carbon emission. An attractive and effective method for converting solar energy to hydrogen energy is photocatalytic water splitting over semiconductors. This study investigated the photocatalytic conversion of formic acid solution to hydrogen using visible light (150 W, 350 < λ < 800 nm). The resultant materials were well characterized by high-resolution transmission electron microscope (HR-TEM), X-ray diffraction (XRD), scanning electron microscopy/energy dispersive X-ray (SEM/EDX), and UV-Vis spectra. The study aimed at utilizing organic sacrificial agents in water, modeled by formic acid, in combination with visible light driven photocatalysts to produce hydrogen with high efficiencies. CdS/TiO2-WO3 ternary hybrid was used as photoactive composite. Microwave induced titanate nanotubes (TNTs) were used as the main carrier to incorporate with CdS for the reason that it holds higher surface area than TiO2. The optimized CdS content is 28 wt% and the production rate of 28 wt%CdS/TNTs achieved 179.35 μmol．h-1. Furthermore, WO3 was physically mixed with the optimized CdS/TNTs binary hybrid. The enhanced photocatalytic activity could be attributed to the electron transfer from CdS to TiO2 to WO3 through the interfacial potential gradient in the ternary hybrid conduction bands, which effectively reduces the chance of charge recombination compared with the binary hybrids. The hydrogen production rate reached 212.68 μmol．h-1. Coating of platinum metal onto the WO3 could further promote the reaction. Results showed that 0.2 g 0.1 wt%Pt/WO3 + 0.2 g 28 wt%CdS/TNTs had the best hydrogen production rate of 428.43 μmol．h-1 , which was more than double compared with CdS/TNTs+ WO3.

碩士
中原大學
化學研究所
100
Asymmetric crystal structure of zinc oxide (ZnO) has a very wide bandgap, the defect structure of non-stoichiometric, high transmittance, high refractive index and nonlinear optical coefficient, and has excellent dielectric, piezoelectric wisdom of the nature of the profiles of the pyroelectric, acousto-optic and optoelectronic materials. Nanostructures of zinc oxide is not only low-cost and easy synthesis of the past decade, such as nanowires, nano-ring with nanometer and nano comb synthesis has also been land continued the successful development of which the nanowires and nano the most widely used in the column. The purpose of this study is to use the chemical solution method, the growth of nano- zinc oxide on the silicon substrate under the mixing ratio of the same geometric concentration of zinc nitrate and hexamethylene tetramine. The ZnO/TiO2 nano-rods process , in the silicon substrate of different impregnated TiO2 time , the formation of ZnO/TiO2 nano-rods surface structure and optical excitation changes. The ZnO/CdS nano-rods process, the silicon substrates of different impregnated CdS time, and the formation of ZnO/CdS nano-rods surface structure and optical excitation changes.

碩士
國立高雄應用科技大學
化學工程與材料工程系碩士在職專班
101
Visible-light responsive evolution of hydrogen on Pt/CdS/N-doped mesoporous TiO2 from photocatalytic water splitting Student：Yao-Zhang Huang Advisors：Dr. Shou-Heng Liu Department of Chemical and Materials Engineering National Kaohsiung University of Applied Sciences Abstract A simple method was developed to fabricate CdS/nitrogen doped mesoporous TiO2 through evaporation induced self-assembly by using an ionic liquid simultaneously as nitrogen sources and a mesopore creator and Cd(NO3)2 as Cd precursors, respectively. Then, the CdO on nitrogen doped mesoporous TiO2 can be ion exchanged with Na2S to form CdS/N-doped mesoporous TiO2 photocatalyst. Finally, different amounts of Pt were deposited on CdS/N-doped mesoporous TiO2 by impregnation method. These Pt/CdS/N-doped mesoporous TiO2 samples were fully characterized by a series of spectroscopic and analytical techniques, such as small- and large-angle X-ray diffraction (XRD), N2 adsorption-desorption isotherms, transmission electron microscopy (TEM), Raman, ultraviolet-visible (UV-vis) diffuse reflectance and X-ray photoelectron (XPS) spectroscopies. Photocatalytic splitting of water by these photocatalysts under visible light was also performed in this stduy. The UV-vis spectra indicated that absorbance of CdS/N-doped mesoporous TiO2 red-shifted to visible area (ca. 510 nm). Moreover, after depositing Pt, the intensity of visible light absorption was significantly enhanced. In the photocatalytic splitting of water under visible light, we found that higher amounts of Pt on CdS/N-doped mesoporous TiO2 could enhance hydrogen evolution, which may due to the fact that Pt metals hindered recombination rate of electron-hole. Keywords: nitrogen-doping mesoporous TiO2, Pt, CdS, EISA, water splitting by visible light.

碩士
國立高雄應用科技大學
化學工程與材料工程系博碩士班
101
In this study, various methods including indirect and direct deposition and ionic exchange with/without bifunctional linker (MPA) were developed to prepare CdS quantum dots / nitrogen-doped mesoporous titania during evaporation-induced-self-assembly (EISA) process. A variety of different spectroscopic and analytical techniques, such as small- and wide-angle powder X-ray diffraction (XRD), Brunauer-Emmet-Teller (BET) analysis, Raman scattering spectroscopy (Raman), small angle X-ray scattering (SAXS), UV-visible spectroscopic (UV-vis), Fourier transform infrared (FT-IR), X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM) were used to characterize the physicochemical properties of various materials. Photocatalytic splitting of water by the synthetic photocatalysts under visible light was also examined in this study. Among all CdS quantum dots / nitrogen-doped mesoporous titania, it the SAXS and BET results indicated that the photocatalysts prepared via ion-exchange method had the better mesoporous structure with highest specific surface areas of 69.4 m2/g. It was also found the more CdS quantum dots were deposited would lead to the decreased specific surface areas. It was observed that UV-visible reflectance spectra suggested that red shifted to the visible region (approximately 500 nm) upon the deposition of CdS quantum dots onto nitrogen-doped mesoporous titania. Among all the prepared photocatalysts under visible-light photocatalytic splitting of water, the photocatalysts fabricated by ion-exchange method had the highest amount of hydrogen production. This result showed that the mesoporous structure of photocatalysts with high specific surface areas and optimum CdS quantum dots would be favorable for photocatalytic evolution of hydrogen under visible light irradiation.

博士
國立成功大學
化學工程學系碩博士班
99
The method of successive ionic layer adsorption reaction (SILAR) was used to assemble cadmium sulfide (CdS) and cadmium selenide (CdSe) onto mesoporous TiO2 films. CdS/CdSe co-sensitized photoelectrodes were prepared and applied for photoelectrochemical hydrogen generation. The results show that the CdS/CdSe co-sensitized photoelectrodes have a complementary effect on the light harvest, and furthermore, the performance of the electrodes is strongly dependent on the order of CdS and CdSe with respected to the TiO2. Dark current and flat-band measurements revealed that TiO2/CdS has a Fermi-level higher than that of TiO2/CdSe while both Fermi-levels of TiO2/CdS/CdSe and TiO2/CdSe/CdS locate between those of TiO2/CdS and TiO2/CdSe, which implies energy level reorganization occurs at the CdS/CdSe interface. The ultraviolet photoelectron spectroscopy (UPS) analysis showed an upward shift of CdSe conduction band edge in the TiO2/CdS/CdSe, sustaining the inference mentioned above. Therefore, TiO2/CdS/CdSe electrode possess a stepwise structure of energy levels, which is advantageous to the electron injection and hole regeneration in the photoelectrode. The saturated photocurrent achieved by the TiO2/CdS/CdSe electrode is 14.9 mA/cm2 (AM1.5 100 mW/cm2, UV cut-off) which is three times the values obtained by the TiO2/CdS and TiO2/CdSe. By using zinc sulfide as a passivation layer to improve the stability and reduce the leakage current, the corresponding hydrogen evolution rate measured for the TiO2/CdS/CdSe/ZnS electrode is 220 ?mol/cm2h. Time resolved photoluminescence (PL) and open-circuit photovoltae decay (OCVD) experiments revealed that the photogenerated electrons in the TiO2/CdS/CdSe have higher injection efficiency, but lower recombination rate to the electrolyte, attributable to the stepwise structure of band-edge levels constructed by the effect of the energy level alignment. Furthermore, TiO2/CdS/CdSe co-sensitized electrode was utilized to fabricate all-solid-state quantum dot sensitized solar cells (QD-SSCs) by using an organic hole transport material (Spiro-OMeTAD), instead of liquid electrolytes. An overall conversion efficiency of 0.65 % (AM 1.5, 100 mW/cm2) was obtained for the TiO2/CdS/CdSe electrode of 2 μm in thickness. Moreover, diisooctyl phosphonic acid (DIOPA) and benzenethiol derivatives were used as surface-modifying agents of the TiO2/CdS/CdSe electrode. It was found that the dipole-moment induced by the surface-modified layers can inhibit the charge recombination, facilitate charge injection from QDs to TiO2, and therefore, enhance photovoltage and photocurrent of the QD-SSC. The overall conversion efficiency achieved by the TiO2/QDs-BTOMe-DIOPA electrode is 0.88%.

The progresses of nanoparticles (NPs) research have been passed through several advancements, such as simple spherical NPs to different shapes (anisotropic), hollow, core/shell, doped, movable core/shell or yolk shell, etc. These NPs have more advanced properties in several applications, such as catalysis, biomedical, electronics, solar cells, sensors, and so on because of high surface area to volume ratio, the presence of more loosely bound surface atoms, etc. When the particles are made of multimaterials it’s not only show improved property of the main material but also developed multifunctionality. Because of these reasons the multimaterials NPs are continuously drawing significant research attentions in the recent years. Under the multi-materials nanoparticles category, doped nanoparticles are also considered as an important class. This thesis is focused on synthesis, characterization, properties, and applications of Ag doped semiconductor nanoparticles. More specifically, TiO2, CdS, and ZnS were considered as the host materials and Ag as the dopant to form single, core/shell, hollow, and hollow bi-layer NPs for the applications in visible light induced photocatalytic degradation of organic compounds (nitrobenzene, metronidazole, methylene blue dye), antifungal agent (against Fusarium solani and Venturia inaquaelis), and sensor for the detection of arsenic and fluoride ions in aqueous media. The abstracts of the studied works are organized sequentially in the following paragraphs. Continuous increasing consumption of antibiotics in health care results to increase concentration of these compounds in surface water through wastewater treatment systems, which in turn, cause adverse effects on the aquatic ecosystems of the receiving water bodies, because of the intrinsic biological activity of these compounds. However, there are limited efforts on remediation of water pollution because of antibiotics using an effective and clean technology. In this study, photocatalytic activity of TiO2, CdS, and ZnS semiconductor nanoparticles were employed to degrade the metronidazole antibiotic in visible light irradiation. The particle size of pure TiO2, CdS, and ZnS was 33.39 ± 1.67, 4.06 ± 0.63, and 5.85 ± 0.5 nm, respectively. The particle size of Ag doped TiO2, CdS, and ZnS was 27.6 ± 2.08, 3.44 ± 0.76, and 4.91 ± 0.45 nm, respectively. The maximum degradation efficiencies of the pure TiO2, CdS and ZnS nanoparticles were 80.78, 82.46, and 81.66%, respectively. These particles were also modified by silver doping to improve its degradation efficiency. Doping of silver greatly enhanced the degradation efficiency of these nanoparticles. The particular concentrations of silver dopant were 1.00, 1.5, and 1.25% for TiO2, CdS, and ZnS nanoparticles for achieving the maximum degradation efficiency and the corresponding maximum degradation efficiencies were 94.39, 94.9%, and 95.11%. The basic mechanism of doping and the photocatalytic processes was explored in detail. A kinetic study of the degradation reaction shows first order kinetics fits well for all three cases. The reusability and stability of these photocatalyst were confirmed by the cyclic degradation test. In addition to the antibiotics, contamination of water because of other organic pollutants, especially synthetic dyes, causes severe environmental problems because of its toxic nature to microorganisms, aquatic life, and human beings. In this regard, an effective and clean remediation process for the remediation of dye contaminated effluent waters becomes more demanding to reduce the environmental impact. This section reports the photocatalytic behaviour of methylene blue using pure and silver doped semiconductor heterogeneous nanocatalysts (TiO2, CdS, and ZnS) under visible light. The photodegradation studies show there is a significant enhancement in degradation efficiency of all three nanoparticles after silver doping. For all nanoparticles, there is an optimum doping concentration to get the maximum degradation efficiency, which again depends on the material. The maximum degradation efficiencies for the three Ag doped TiO2, ZnS, and CdS nanoparticles were 95.9, 95.33, and 94.99% for 1.00, 1.25, and 1.50% Ag, respectively. The first order rate constant value of 1.00% Ag doped TiO2, 1.5% Ag doped CdS, and 1.25% Ag doped ZnS is 5.21, 5.72, and 7.71 times higher compared to their respective pure nanoparticles. The maximum degradation efficiency with minimum doping concentration among all three materials studied here was again found for TiO2. Further, silver doped hollow TiO2 (Ag-h-TiO2) nanoparticles were also synthesized by a sacrificial core (AgBr) method to enhance the surface area for higher photocatalytic activity. The Ag doping and the core removal was done simultaneously during the dissolution of the core in (NH4)OH solution. The mean particle size of synthesized Ag-h-TiO2 nanoparticles was 17.76 ± 2.85 nm with the wall thickness ~2.5 nm. The hollow structured nanoparticles have the specific surface area of 198.3 m2/g, where as solid TiO2 nanoparticles have the specific surface area of 95.1 m2/g. The suitability of this synthesized hollow nanoparticles as photocatalyst were tested for the photocatalytic degradation of three important different classes of organic compounds such as nitrobenzene (NB), metronidazole (MTZ) antibiotic, and methylene blue dye (MBD) in aqueous solution under irradiation of visible light. The maximum NB degradation was obtained 95.5%, and the metronidazole degradation efficiency was found to be 96.55 and 94.77% under the irradiation of visible light for the initial MTZ concentration of 15 and 30 mg/L with catalyst dose of 0.5 g/L. Photodegradation studies show there is a significant enhancement of the degradation efficiency of the TiO2 after the hollow structure formation and silver doping. The recycling tests of the catalysts show only ~ 10% decrease in efficiency for NB and MTZ degradation after sixth cycle of reuse. The light emission capacity in terms of quantum yield (QY) is enhanced by 18.7% for Ag-h-TiO2 than that of pure TiO2 nanoparticles. The above mentioned hollow TiO2 NPs were also used as photoinduced antifungal agent. The chemical based pesticides are widely used in agricultural farming to protect crops from insect infestation and diseases. However, the excessive use of highly toxic pesticides causes several human health (neurological, tumour, cancer) and environmental problems. So, nanoparticles based green pesticides are of special importance in recent years. Antifungal activities of the pure and Ag doped (solid and hollow) TiO2 nanoparticles were studied against two potent phytopathogens, Fusarium solani (causing Fusarium wilt disease to potato, tomato etc.) and Venturia inaquaelis (causing apple scab disease) and found hollow nanoparticles are more effective than other two. The antifungal activities of the nanoparticles enhanced further under visible light exposure against these two phytopathogens. Fungicidal effect of the nanoparticles depends on different parameters, , such as particle concentration, and intensity of visible light. The minimum inhibitory dose of the nanoparticles for V.inaquaelis and F.solani are 0.75 and 0.43 mg/plate. Presence of Ag as a dopant helps to the formation of stable Ag-S and di-sulfide bond (R-S-S-R) in cellular protein, which leads to the cell damage. During photocatalysis generated OH radicals loosen the cell wall structure and finally lead to the cell death. The mechanisms of fungicidal effect of nanoparticles against these two phytopathogens are supported by biuret and triphenyl tetrazolium chloride analyses, and field emission electron microscopy. Apart from the fungicidal effect, at very low dose (0.015 mg/plate) the nanoparticles are successfully arrest production of toxic napthoquinone pigment for F.solani which is related to the fungal pathogenecity. The nanoparticles are found to be effective to protect spoiling of potato affected by F.solani or other fungus. The doped nanoparticles can also be used effectively for the easy detection of toxic ions in water. In this regard, fluoride ion detection has taken a considerable research interest in recent years because of its typical nature. It is an essential anion for biological and medical systems, as well as for some industrial applications. But, the fluoride ions above its permissible level can cause different diseases, such as fluorosis, urolithiasis, kidney failure, cancer, and even leading to death. Because of this reason a simple and low cost method is highly desirable for the detection of fluoride ion. In this study a fluorometric method based on Ag-CdS/Ag-ZnS nanoparticle is developed for the fluoride ion detection. The developed nanoparticles were of size range 5.92 ± 0.76 nm with shell layer of 0.75 nm and it showed the quantum yield of 77.57%. The method was tested in aqueous solution at different pH. The selectivity and sensitivity of the fluorescence probe was checked in the presence of other anions (Cl-, Br-, I-, OH-, NO3- SO42-, HCO3-, HPO42-, CH3COO-, H2PO4-). The fluoride ion concentration was varied in the rage 190 – 22,800 μg/L and the lower detection limit was obtained as 99.7 μg/L. Arsenic poisoning from drinking water is also an important global issue in recent years. Because of high level toxicity of arsenic to human health, an easy, inexpensive, and low level and highly selective detection technique is of great importance to take any early precautions. This study reports the synthesis of Ag doped hollow CdS/ZnS bi-layer (Ag-h-CdS/ZnS) nanoparticles for easy fluorometric determination of As(III) ions in aqueous phase. The hollow bi-layer structures are synthesized by a sacrificial core method using AgBr as the sacrificial core and the core is removed by dissolution in ammonium hydroxide solution. The synthesized nanoparticles were characterized by using different instrumental techniques. The particle size of Ag-h-CdS/ZnS nanoparticles is ~ 76.02 ± 2.47 nm with the shell thickness of CdS layer is 1.5 nm and ZnS layer is 1.8 nm. The QY of the Ag-h-CdS/ZnS nanoparticles is 88.14%. A good linear relationship is obtained between fluorescence quenching intensity and the As(III) concentration in the range of 750 – 22500 ng/L at neutral pH with a limit of detection as low as 226 ng/L.

碩士
大同大學
化學工程研究所
91
It has been found that the nano-sized materials are very helpful in the solid polymer electrolyte and therefore it has become an important research field. In this study, the solid polymer electrolyte have been prepared based on poly(ethylene oxide) (PEO) blended with different weight percentages of alkali metal salt (LiClO4). The X—ray diffraction and DSC studies reveal the crystallization of PEO, which is reduced with increasing the content of LiClO4. From the AC impedance measurements, the ionic conductivity of the PEO/LiClO4 SPE systems increases initially with decreasing [EO]/[Li+] ratio and reaches maximum value (7.13 × 10 — 6 S/cm) at the [EO]/[Li+] ratio of 10, but decreases as the [EO]/[Li+] ratio is further decreased. It can be found that SPE system blended with nanoparticles ((TiO2, SiO2, and CdS), and tetraethoxysilane (TEOS)) can enhance the ionic conductivity, except for SiC. The highest ionic conductivity of P(EO)8LiClO4 blended with 3 wt% of TEOS can reach 7.83 × 10 — 4 S/cm at room temperature, which is close to those of lithium liquid electrolyte lithium batteries (10 — 2 ~ 10 — 3 S/cm) used extensively at present. The ionic conductivities of P(EO)8LiClO4 SPE system blended with 3 wt% of SiO2, TiO2, and CdS is 2.9 × 10 — 4, 3.9 × 10 — 4, and 4.83 × 10 — 4 S/cm, respectively. In other words , the order of ionic conductivity for SPE blended with 3 wt% of nanoparticles is TEOS ＞ CdS ＞ TiO2 ＞ SiO2 ＞ SiC. The result can be confirmed by SEM micrographs. It can be found that SPE system blended with nanoparticles (TiO2, SiO2, and CdS) can improve the tensile strength stability of SPE film.

No
The objective of this review is to provide an overview concerning what the authors believe to be the most important photoelectrochemical techniques for the study of semiconductor nanoparticles. After a short historical background and a brief introduction to the area of photoelectrochemistry, the working principles and experimental setups of the various static and dynamic techniques are presented. Experimental details which are of crucial importance for their correct execution are emphasized, and applications of the techniques as found in the recent research literature as applied to semiconductor nanoparticles are illustrated.