Academic literature on the topic 'Titanium Dioxide Cadmium Sulfide'

An unprecedented morphology of a 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 reported here.

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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 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.

Research into renewable energy sources is crucially increasing to counteract the ever more concerning impact of non-renewable sources. Theoretically, Quantum Dot Solar Cells (QDSCs) can achieve much greater efficiencies than current, commercial solar cells, but its expansion is still in its very early stages of scientific study and development. In this project TiO2, one of the most efficient and cost-effective photocatalysts, is coupled with Cadmium Selenide (CdSe) Quantum Dots (QD) in a study of interfacial charge transfers. Thus far, in other studies, CdSe QDs have shown some of the most promising results of QDSCs. EPR spectroscopy has been used here to study charge transfer processes in CdSe quantum dot (QD) sensitised titania. Visible light excitation of QDs directly adsorbed onto titania surfaces causes electron transfer to the titania, producing characteristic EPR signals of trapped electrons in the titania. Under ultraviolet excitation the trapped electron signals seen in titania alone are suppressed in the presence of directly adsorbed quantum dots, as is the formation of superoxide in the presence of oxygen. These observations suggest that reverse electron transfer from the titania to the QDs can also occur. No visible light excited electron transfer occurs in the case of QDs attached to the titania surface via bi-linker molecules, but under ultraviolet excitation a similar suppression of electron trapping in the titania phase is seen. These results show that the nature of the interface between the QDs and the titania phase is crucially important in the electron transfer processes in both directions. The study also looks at the pitfalls of synthesis techniques used for making the CdSe QDs as well as the method of attaching it to the TiO2. Ionic deposition, which generally resulted in the best photocurrents in other studies, was discovered early on this project produced very impure samples. Direct Adsorption produces low titania surface coverage, which can potentially be improved. Whereas the lack of discussion in literature of clear purification methods in synthesis techniques for attaching QDs via a bi-linker molecule, through ligand exchange, causes a significant drawback in the study of such systems.

This study focuses on the visible light response of hetero-structures of TiO2-graphene- MoS2 for solar energy harvestings. The commercial P25 TiO2 nano-particles, and selfprepared layered reduced graphene oxides (RG) and MoS2 were assembled for the targeted hetero-structure materials as visible-light responsible solar harvesting cocatalysts. The hydrothermal method was applied for nano-material synthesis, the reduction of graphene oxides, and bonding formation. Multiple characterization methods (SEM-TEM, XRD, XPS, UV-VIS, PL, FT-IR, TGA) have been applied to understand the electron-hole pair separation and recombination, and performance tuning in their visible-light photo-catalysis rhodamine B (Rh.B) degradations process Compared to TiO2, an obvious red shift of light absorption (from 3.1 eV to 2.6 eV) of the as-prepared RG-TiO2 was observed by UV-vis analysis, and an enhanced photocatalytic degradation of the Rhodamine B (Rh.B) using the as-prepared RG-TiO2 was also observed in a Xe lamp exposure test. The explication of these two approaches to photocatalytic improvements were concluded as the energy gap changing, the formation of Ti-O-C chemical bonds between TiO2 and RG for charge transfer and the reduction of the band gap, as well as a likelihood of up-conversion photoluminescence mechanism (UCPL). The synthesis temperature was found to be critical factor to control binding formation and agglomeration of nano-materials. The lower and higher temperatures induced ineffective formations of preferable bonding structures and the significant agglomeration. The optimal synthesis temperature was found to be within 120 ℃-150 ℃ in the TiO2-RG system. For better understanding of the Ti-O-C bonding, a heterostructure of TiO2 nanotube arrays with GO (TNA-GO) was synthesized using the Langmuir-Blodgett (LB) assembly method. The band gap of this assemble was very close to the previous TiO2-RG synthesized below 120 ℃, which is very close to that of TiO2 nano-particles. This lead to the conclusion on the significance of the Ti-O-C bonding in the visible-light-responsible photo-catalysis solar harvestings. This study revealed the fundamental mechanisms on the bonding formations and the significant visible-light-response of hetero-structcures between commercial-available, inexpensive and non-toxic TiO2 and layered materials, such as the zero-band-gap graphene and the smaller-band-gap MoS2. This mechanisms understanding will greatly sustain applications of economical-effective and environmental-safe TiO2.

In this study, photoemission spectroscopy (PES) was used to investigate the electronic properties of nanocrystalline titanium dioxide (TiO2), zinc oxide (ZnO), and cadmium selenide (CdSe). Electrospray deposition technique enabled the preparation of thin films in vacuum from a dispersion prepared outside the vacuum chamber. This method also allowed the step-wise formation of interfaces and the monitoring of the evolution of the electronic structure with intermittent PES characterization. The work function of nanocrystalline TiO2 and ZnO was measured with ultraviolet photoemission spectroscopy (UPS) and low-intensity x-ray photoemission spectroscopy (LIXPS). Measurements on environmentally contaminated surfaces revealed an instantaneous and permanent work function decrease of 0.3-0.5 eV upon exposure to ultraviolet radiation during a UPS measurement. The work function reduction is likely to be related to the formation of a surface dipole caused by the photo-chemical hydroxylation of surface defects. This phenomenon was further investigated with regard to its influence on the electronic structure of the indium tin oxide (ITO)/TiO2 interface found in dye-sensitized solar cells. The experiments suggest that UV radiation can cause a small but significant change of the charge injection barriers at the interface. The determined band line-ups revealed electron injection barriers of ~0.3-0.5 eV, while UV radiation caused an increase of about 0.15 eV. This might have the potential to further impede electron transfer to the ITO electrode and affect the performance of solar cell device. Another type of photovoltaic cell using nanocrystalline material is a heterojunction bulk solar cell. Conversion efficiencies of such devices are currently only about 3% due to the inefficient charge separation at interfaces formed by blending organic and inorganic material. An approach to improve efficiencies in such devices is the use of covalently bonded conductive polymer/inorganic hybrid nanocrystals. In this study a prototypical model system was investigated with PES with the aim to develop a measurement protocol that allows the determination of electronic properties for such hybrid materials. The comparison of the relative core-level binding energies of the organics-functionalized CdSe nanocrystal compared to the ligand-free CdSe nanocrystal and the arylselenophosphate ligand material enabled the determination of the electronic structure at the interface. Core-level measurements support the hypothesis that the Se functionality of the organic ligand coordinates to the Cd sites on the nanopthesis surface.

Recent developments on environmental fate models indicate that as nano waste, engineered nanomaterials/nanoparticles (ENM/Ps) could reach terrestrial ecosystems thus potentially affecting environmental and human health. Plants can be therefore exposed to ENM/Ps but controversial data in terms of fate and toxicity are currently available. Furthermore, there is a current lack of information on complex interactions/transformations to which ENM/Ps undergo in the natural environment as for instance with existing toxic compounds. The main aim of current study is to evaluate potential toxicological risks due to the exposure of plants to ENM/Ps in their natural environment, and investigating different routes of exposure (i.e. water and soil). The aim of the first study reported in chapter 1 was to asses behavior and biological effects of titanium dioxide nanoparticles (n- TiO2) (Aeroxide P25, Degussa Evonik) and its interaction with cadmium (CdCl2) in plants using radish seeds (Raphanus sativus parvus) as model species. Radish seeds were exposed to different concentrations of n-TiO2 (range 1-1000 mg/L) and CdCl2 ( range 1-250 mg/L) alone and in combination using a seed germination and seedling growth toxicity test OECD 208. Percentages of seed germination, germination index (GI) and root elongation were calculated. Cell morphology and oxidative stress parameters as glutathione-S-transferase (GST) and catalase activities (CAT) were measured in radish seeds after 5 days of exposure. Z-Average, PdI and Z-potential of n-TiO2 in Milli-Q water as exposure medium were also determined. DLS analysis showed small aggregates of n-TiO2, negative Z-potential and stable PdI in seed’s exposure media. Germination percentage, GI and root length resulted affected by n-TiO2 exposure compared to controls. Exposure of CdCl2 significantly abolished germination % and GI compared to control seeds and a concentration dependent decrease on root elongation was observed against controls (p<0.05). As well, significant decrease of germination %, GI and root elongation was observed in seeds co-exposed to n-TiO2 and CdCl2 at the highest concentrations (1000mg/L n-TiO2 and 250 mg/L CdCl2) compared to co-exposed seeds at low concentration (1mg/L n-TiO2 and 1 mg/L CdCl2) and controls (p<0.05). Root elongation significantly increase compared to controls at the lowest co-exposure concentration (p<0.05). Similarly at intermediate concentrations of 10 and 100 mg/L in co-exposure conditions, n-TiO2 did not affect CdCl2 toxicity. Concerning antioxidant enzymes, a significant increase of CAT activity in seeds exposed to single high n-TiO2 concentration (1000 mg/L) was observed while n-TiO2 (1 mg/ L), CdCl2 (1 and 250 mg/L) and co-exposure resulted significantly decreased compared to controls (p<0.05). Regarding GST activity, a slight increase in seeds exposed to 1000 mg/L n-TiO2 but no significantly was observed, however both n-TiO2 and CdCl2 alone (1 and 250 mg/L, respectively) or in combinations caused a significant decrease in GST activity (p<0.05). Therefore, overall data support the hypothesis that the presence of n-TiO2 do not affect the toxicity of CdCl2 at least at the highest concentration (100 and 250 mg/L) in radish seeds. Morphological alterations in nuclei, vacuoles and shape of radish root cells were observed upon single Cd exposure and not abolished in the presence of n-TiO2. Nevertheless, although n-TiO2 seems not to reduce Cd toxicity at high concentration (up to 250 mg/L), interactions cannot be excluded based on obtained results. The aim of the second study reported in chapter 2 was to assess if the presence of n-TiO2 might affect elutriate toxicity to radish seeds (R. sativus parvus) seeds as a model species. Radish seeds were exposed to 11 soils (elutriates) alone and in combination with 1 mg/L of n-TiO2 collected from an industrial site located in Taranto area (South East of Italy). Exposure of seeds was performed according to OECD (208) guideline. Then, root elongation, percentages of seed germination and germination index% (GI) were analyzed. In addition, levels of several trace elements were also determined in soils in order to assess their level of contamination and effects on root elongation, seed germination and GI% further discussed. Main results revealed that the presence of n-TiO2 seems not affecting root length, GI % and germination% of seeds compared to seeds exposed to elutriates alone with the exception of only 2 sites. Moreover, the absence of any clear relationship between effects of elutriate on radish seed germination and trace elements levels was observed. Only slight but not significant changes based on levels of trace elements present in soil were observed in growth parameters. In particular levels of Co, Ni, Zn, Cu, Ti and Sn seem to affect radish seeds germination more than others. Regarding co-exposed seeds, the presence of n-TiO2 caused 100% of germination of radish seeds. Furthermore, in comparison to exposed seeds to elutriates alone, root length and GI % resulted more stimulated. Only slight effects on GI% and root length were observed which might be linked to interaction of these elements with n-TiO2. Likewise, it seemed that Co, Se, Sb and As in presence of n-TiO2 are responsible for changes on growth parameters. According on the overall results, soil elutriates alone could not be able to show real toxicity of a contaminated soil on seeds germination and future study should be performed in order to assess their suitability in real exposure scenarios. Therefore, based on observed data further investigations are required in order to assess real environmental scenarios where such particles could be present in soils together with existing contaminants such trace elements. The purpose of third study reported in chapter 3 chapter was to assess the impact of n-TiO2 alone and in combination with CdCl2 on germination and growth of radish seeds (R. sativus) exposed in vitro (experiment 1) and in vivo (directly into soils) (experiment 2). In experiment 1(in vitro) radish seeds were exposed to n-TiO2 (1 and 1000 mg/L and CdCl2) and CdCl2 (1 and 250 mg/L) alone and in combination (n-TiO2 1, 10, 100, 1000 mg/L and CdCl2 1, 10, 100, 250 mg/L) using a seed germination and seedling growth toxicity test OECD 208. In experiment 2 (in vivo), radish exposed only to water and then seedling transferred to soils contaminated with n-TiO2 (1 and 1000 mg/L and CdCl2) and CdCl2 (1 and 250 mg/L) alone and in combination (n-TiO2 1, 10, 100, 1000 mg/L and CdCl2 1, 10, 100, 250 mg/L), still following OECD 208 test conditions. Root length, shoot length and numbers of secondary leaves of all plants from the two experiments (1 and 2) were recorded at day 10 and day 21. Growth parameters of radish at both day 10 and day 21 showed that plants from seeds exposed during germination (experiment 1) resulted more affected by single and co-exposure to n-TiO2 and CdCl2 than those exposed directly in soil (experiment 2). Furthermore, presence of CdCl2 at 250 mg/L alone and in combination with 1000 mg/L of n-TiO2 seemed affect the root and shoot length in both experiments 1and 2 at day 10 and day 21. Growth parameter analysis of single and co-exposed groups in experiment 1 at day 10, showed a decrease in root length in all tested plants with exception of those exposed to n-TiO2 (1mg/L), co-exposed to n-TiO2 and CdCl2 (1mg/L and 1mg/L), (10 mg/L and 10 mg/L) and (100 mg/L and 10 mg/L) which showed slight increase compared to control. In experiment 2 at day10 only exposed plants to 1000 mg/kg of n-TiO2 revealed significant increase of root length while other all single and co-exposure groups showed a decrease of root length respect to control. Shoot length in exposed plants to all single and co-exposure groups in both experiments 1 and 2 at day 10 showed a decrease compared to control except plants exposed to n-TiO2 and CdCl2 (100 mg/kg and 10 mg/kg) in experiment 2 which showed an increase. Obtained results on day 21 showed a decrease of root length respect to control on tested plants to all single and co-exposure groups in both experiments 1 and 2 with exception of exposed radish to 1 mg/L of CdCl2 in experiment 1. Shoot length of all tested single and co-exposure groups in experiments 1 and 2 showed a decrease compared to control except radish exposed to 1000 mg/kg of n-TiO2 which revealed an increase in experiment 2. Regarding secondary leaves, in both experiments 1and 2 at day 10 no leaves were shown. On the opposite, (2 leaves) were present at day 21 in most plants exposed to single and in combination, while those exposed to CdCl2 (250 mg/kg), n-TiO2 and CdCl2 (10 and 100 mg/L) and (1000 mg/kg and 250 mg/kg) in experiment 1 showed no leaves. Likewise, exposure n-TiO2 (1000 mg/kg) and co-exposure of n-TiO2 and CdCl2 (10 mg/kg and 100) showed only one secondary leaf in experiment 2 at day 21.

Gasification is an important strategy for increasing the utilization of abundant domestic coal reserves. DOE envisions increased use of gasification in the United States during the next 20 years. As such, the DOE Gasification Technologies Program, including the FutureGen initiative, will strive to approach a near-zero emissions goal, with respect to multiple pollutants, such as sulfur, mercury, and nitrogen oxides. Since nearly one-third of anthropogenic carbon dioxide emissions are produced by coal-powered generation facilities, conventional coal-burning power plants, and advanced power generation plants, such as IGCC, present opportunities in which carbon can be removed and then permanently stored. Gas cleaning systems for IGCC power generation facilities have been effectively demonstrated and used in commercial operations for many years. These systems can reduce sulfur, mercury, and other contaminants in synthesis gas produced by gasifiers to the lowest level achievable in coal-based energy systems. Currently, DOE Fossil Energy’s goals set for 2010 direct completion of R&D for advanced gasification combined cycle technology to produce electricity from coal at 45–50% plant efficiency. By 2012, completion of R&D to integrate this technology with carbon dioxide separation, capture, and sequestration into a zero-emissions configuration is targeted with a goal to provide electricity with less than a 10% increase in cost of electricity. By 2020, goals are set to develop zero-emissions plants that are fuel-flexible and capable of multi-product output and thermal efficiencies of over 60% with coal. These objectives dictate that it is essential to not only reduce contaminant emissions into the generated synthesis gas, but also to increase the process or system operating temperature to that of humid gas cleaning criteria conditions (150 to 370 °C), thus reducing the energy penalties that currently exist as a result of lowering process temperatures (−40 to 38 °C) with subsequent reheat to the required higher temperatures. From a historical perspective, the evolution of advanced syngas cleaning systems applied in IGCC and chemical and fuel synthesis plants has followed a path of configuring a series of individual cleaning steps, one for each syngas contaminant, each step controlled to its individual temperature and sorbent and catalyst needs. As the number of syngas contaminants of interest has increased (particulates, hydrogen sulfide, carbonyl sulfide, halides such as hydrogen chloride, ammonia, hydrogen cyanide, alkali metals, metal carbonyls, mercury, arsenic, selenium, and cadmium) and the degree of syngas cleaning has become more severe, the potential feasibility of advanced humid gas cleaning has diminished. A focus on multi-contaminant syngas cleaning is needed to enhance the potential cost savings, and performance of humid gas cleaning will focus on multi-contaminant syngas cleaning. Groups of several syngas contaminants to be removed simultaneously need to be considered, resulting in significant gas cleaning system intensification. Intensified, multi-contaminant cleaning processes need to be devised and their potential performance characteristics understood through small-scale testing, conceptual design evaluation, and scale-up assessment with integration into the power generation system. Results of a 1-year study undertaken by DOE/NETL are presented to define improved power plant configurations and technology for advanced multi-contaminant cleanup options.