This Thesis deals with the construction of an electrochemical cell with two types of integrated composite electrodes based on carbon films. Using these electrodes, the voltammetric behavior of environmental pollutant triclosan (5-chlor-2-(2,4- dichlorophenoxy)phenol) was studied. For the construction of composite electrodes, graphite and glassy carbon were used as conductive microparticles. Several types of polymers served as the nonconductive binder. For the measurements, combinations of graphite with polystyrene and graphite with polycarbonate were selected as optimum materials. From the dependence of peak heights on solution composition, a mixture of a buffer of pH 7 and methanol (1:9, V/V) was selected as the optimum medium. In this medium, concentration dependences were measured; calculated triclosan detection limit were 0,49 µmol dm-3 for carbon polystyrene composite electrode and 0,25 µmol dm-3 for carbon polycarbonate composite electrode, respectively. The possibility of further increasing the sensitivity of the determination by the accumulation step was studied. Accumulation of triclosan on carbon polystyrene composite electrode was observed, but the increase in response was connected with the loss of repeatability. Accumulation of triclosan on carbon polycarbonate composite electrode was...

The application of electrochemical methods for the characterization of colloidal quantum dots (QDs) attracts considerable attention as these methods may allow for monitoring of some crucial parameters, such as energetic levels of conduction and valence bands as well as surface traps and ligands under real conditions of colloidal solution. In the present work we extend the applications of cyclic voltammetry (CV) to in situ monitoring of degradation processes of water-soluble CdTe QDs. This degradation occurs under lowering of pH to the values around 5, i.e. under conditions relevant to bioimaging applications of these QDs, and is accompanied by pronounced changes of their photoluminescence. Observed correlations between characteristic features of CV diagrams and the fluorescence spectra allowed us to propose mechanisms responsible for evolution of the photoluminescence properties as well as degradation pathway of CdTe QDs at low pH.

Diese Arbeit beinhaltet unsere Studien an selbstorganisierenden Monoschichten (engl. SAM = self- assembled monolayer) einiger aromatischer Thiole auf Gold- und Kupferoberflächen. Die Bildung von Monoschichten von Thiophenol, 4-Mercaptophenol, 4-Nitrothiophenol, 4-Aminothiophenol, 1,4-Dithiobenzol, 4-Mercaptopyridin und 2-Mercaptopyridin auf Au und Cu wurde untersucht und charakterisiert. Das abschirmende Verhalten und die strukturelle Anordnung dieser Monoschichten wurden mit Hilfe elektrochemischer und spektroskopischer Methoden geprüft und bestimmt. Zyklische Voltammetrie und oberflächenverstärkte Raman Spektroskopie wurden intensiv zur Aufklärung von Elektronentransferreaktionen an diesen mit SAMs modifizierten Oberflächen genutzt. Elektrochemische Studien von Monoschichten aus Thiophenol, 4-Mercaptophenol, 4-Nitrothiophenol, 4-Aminothiophenol, 1,4-Dithiobenzol, 4-Mercaptopyridin und 2-Mercaptopyridin in 0,1 M wässriger KClO4-Lösung lassen schlussfolgern, dass diese Moleküle schwefelseitig an die Substratoberfläche gebunden sind. In 0,1 M wässriger KClO4-Lösung aufgenommene zyklische Voltammogramme an Gold- und Kupferoberflächen, welche mit oben genannten, aromatischen Thiolen beschichtet wurden, legen nahe, dass Adsorptionsschichten von Thiophenol und 1,4-Dithiobenzol eine stärkere Tendenz zum Abschirmen besitzen als andere. Durch das Einbringen von Kupferproben, welche mit genannten aromatischen Thiolen behandelt wurden, in 0,1 M Silbernitrat-Lösung können sehr leicht Silber-Nanodendritstrukturen erhalten werden. Abscheidezeit und Konzentration der Silbernitrat-Lösung haben einen großen Einfluss auf das Wachstum der Silber-Nanodendritstrukturen auf den modifizierten Kupferproben. Diese Silber-Nanodendritstrukturen besitzen eine hohe katalytische Aktivität hinsichtlich der Oxidation von Hydroquinon. Untersuchungen zur Korrosion an polykristallinem Kupfer, welches mit obigen aromatischen Thiolen modifiziert wurde, in 0,1 M Silbernitrate-Lösung ließen vermuten, dass dieses Kupfersubstrat mehr anodisches Verhalten zeigte als reines Kupfer bei ähnlichen Bedingungen. Zyklische Voltammetrie an wie oben behandeltem Kupfer in 0,1M wässriger KClO4-Lösung zeigte, dass die Geschwindigkeit der Kupferauflösung bei diesen Messungen erhöht war gegenüber anderen, in welchen reines Kupfer bei identischen Bedingungen eingesetzt wurde. / It deals with our studies on self-assembled monolayers of aromatic thiols on gold and copper surfaces. Monolayer formation of thiophenol, 4-mercaptophenol, 4-nitrothiophenol, 4-aminothiophenol, 1,4-dithiobenzene, 4-mer¬cap¬to¬pyridine and 2-mercaptopyridine on Au and Cu surfaces was studied and characterized. The blocking behaviour and structural arrange¬ments of these monolayers were evaluated and characterized using electrochemical and spec¬troscopic techniques. Cyclic voltammetry and surface enhanced Raman spectroscopy were extensively used for the study of electron transfer reactions on these SAM modified surfaces. Electrochemical and spectroelectrochemical studies of thiophenol, 4-mercaptophenol, 4-nitrothiophenol, 4-aminothiophenol, 1,4-dithiobenzene, 4-mercaptopyridine and 2-mercaptopyridine monolayers in aqueous solution of 0.1 M KClO4 suggest that these molecules adsorbed to substrate. Cyclic voltammetry of gold and copper covered with these aromatic thiolates recorded in aqueous solution of 0.1 M KClO4 suggests that adlayers of thio¬phenol and 1,4-dithiobenzene exhibit more blocking behavior than the other ones. Silver nanodendritic structures are easily produced by placing copper samples modified with these aromatic thiolates into 0.1 M silver nitrate solution. Deposition time and concentration of silver nitrate solution have great influence on growing up silver nanodendritic structures on the surface of modified copper samples. These silver nanodendritic structures exhibit electrocatalytic activity towards the oxidation of hydroquinone. Corrosion investigation of polycrystalline copper modified with these aromatic thiolates in 0.1 M silver nitrate solution suggest that copper substrate might be more anodic compared to bare copper under identical condition. Cyclic voltammetry of copper modified with these aromatic thiolates suggests that the rate of dissolution copper in aqueous solution of 0.1 M KClO4 is higher than bare copper in the same condition.

Optimum detergent dosage during a washing process depends on water quality, degree of pollution and quantity of laundry. Particularly, water quality is an important factor. Other parameters like carbonate- or non-carbonate hardness and calcium / magnesium (Ca / Mg) ratio in addition to total hardness of water have an impact on the amount of detergent. This work discusses the possibilities realizing a detergent sensor that measures important parameters for the washing process and assess the ideal necessary amount of detergent during the washing process. The approach is to combine impedance spectroscopy with cyclic voltammetry in order to determine both water quality and concentration of detergent in the suds which build up the basis for an optimum detergent dosage. The results of cyclic voltammetry show that it is possible to identify the Ca / Mg ratio and the carbonate hardness separately, which is necessary for the optimization of the washing process. Impedance measurements identify total hardness and detergent concentrations.

[pt] A busca pela diminuição da dependência de combustíveis fósseis faz com que a ciência avance, diariamente, na utilização de combustíveis ecológicos, como o H2. Uma das formas de sua obtenção é através da fotocatálise. Esse processo consiste em uma reação catalítica com o uso de energia, na forma de luz. A fotólise da água é amplamente utilizada, principalmente com luz solar como fonte luminosa, que é abundante e reduz os custos de sua produção. O desempenho desta reação depende da posição das bandas de condução (BC) e valência (BV) do fotocatalisador. O TiO2 é utilizado como fotocatalisador em diversas reações, inclusive para a produção de H2. Os fotocatalisadores utilizados na forma de pós nanométricos apresentam dificuldade de separação após a reação. A transformação do pó em um material compacto é uma alternativa para retirá-lo do meio reacional evitando perdas e custos com separação. Desse modo, a compactação do pó é uma alternativa para facilitar sua reciclagem. O principal método de sua produção é pelo processo de sinterização, que envolve temperaturas elevadas (geralmente, 75 por cento do ponto de fusão do material) e longo tempo, podendo durar até dias. Para diminuir os gastos energéticos, o processo de sinterização a frio é uma opção, que consiste na densificação do material com uso de pressão e um solvente (aquoso ou não) e, temperaturas de sinterização de até 500 Graus C. O objetivo do estudo consistiu na produção de pastilhas de TiO2, comercial, e P25, através de uma variação do método de sinterização a frio, onde aplicou-se a pressão no pó, junto com o solvente, antes de seu tratamento térmico. As pastilhas produzidas foram caracterizadas pelas técnicas de TGA/DSC, XRD, MEV, CV, e DRS. / [en] The quest to reduce dependence on fossil fuels makes science advance, daily, in the use of ecological fuels, such as H2. One of the ways to obtain it is through photocatalysis. This process consists on a catalytic reaction using energy, in the form of light. Water photolysis is widely used, mainly with sunlight as a light source, which is abundant and reduces production costs. The performance of this reaction depends on the position of the conduction (CB) and valence (VB) bands of the photocatalyst. TiO2 is used as a photocatalyst in several reactions, including the production of H2. Photocatalysts used in the form of nanometric powders have difficulty in separating after the reaction. The transformation of the powder into a compact material is an alternative to remove it from the reaction medium, avoiding losses and costs with separation. Thus, the compaction of the powder is an alternative to facilitate its recycling. The main method of its production is through the sintering process, which involves high temperatures (generally 75 percent of the material s melting point) and a long time, which can last up to days. To reduce energy costs, the cold sintering process is an option, which consists of densifying the material using pressure and a solvent (aqueous or not) and sintering temperatures of up to 500 C degrees. The aim of the study was the production of commercial TiO2 and P25 pellets, through a variant of the cold sintering method, where pressure was applied to the powder, with the proper solvent, before the heat treatment. The pellets produced were characterized by the techniques of TGA/DSC, XRD, SEM, CV, and DRS.

Rare earth and actinide metals, critical to security, medicine, and the economy, have been processed through methods such as solvent extraction and electrorefining. To minimize radiological waste and improve yield, a 'chloride volatility' process--also known as the chlorination and volatilization process (CVP)--has been proposed and demonstrated for processing rare earths. The process takes advantage of the low vapor pressure of rare earth chlorides (<700 >°C), CaCl2 was added to LaCl3 to lower the melting temperature. LaCl3 electrochemical behavior has not previously been studied in CaCl2. Cyclic voltammetry (CV) and square wave voltammetry (SWV) were applied to LaCl3 salts in CaCl2-LiCl and CaCl2 to study the metal ion behavior. Various electrode materials were compared at low CV scan rates (s-1) to determine compatibility with chlorine gas evolution. Experiments of eutectic LaCl3-CaCl2 were performed and analyzed to determine the efficacy of chlorine gas generation via electrolysis for the CVP. Through galvanostatic electrolysis, oxidation of chloride ions and subsequent chlorination of rare earth was demonstrated, with cerium chosen as the representative rare earth metal. Through a quadrupole mass spectrometer plumbed in line with the electrolytic cell, the quality of the generated gas was analyzed.

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