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Conducting polymer is a rapidly developing area of research due to its potential in combining the physical properties of polymers with electrical properties previously found only in inorganic systems. These conducting polymers owe their unique properties to a conjugated polymer backbone and become conducting upon oxidation or reduction. Melanin, a biopolymer, possess a conjugated backbone required of a conducting polymer, and has shown properties of an amorphous semiconductor. However, there has not been much study done in this area despite its potential, and this is partially due to the lack of processing methods as melanin is generally synthesised as an intractable powder. Thus, a better synthetic method was required, and a possible solution is the use of electrochemical synthesis. In our previous study we have shown that melanin can be synthesised electrochemically as a free-standing film, which was the first step towards the use of melanin as a bulk material. This project aims to continue from this preliminary work, investigating the various synthetic parameters and possible modifications as well as investigating possible applications for the electrochemically synthesised melanin film.

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<p dir="ltr">Developing high-nitrogen materials is highly important to industries, such as pharmaceuticals and energetic materials development. The production of such materials is often wrought with hazardous conditions that raise manufacturing costs and produce toxic waste streams. This is often observed using heavy-metal redox reagents such as potassium permanganate, lead acetate, zinc, and silver metal. Elucidating novel synthesis techniques to alleviate these issues is highly important for reducing environmental toxicity and lowering reaction costs. One green technique that has gained popularity in the past few decades is synthetic organic electrochemistry. Electrochemistry is a technique that utilizes the direct flow of electrons to drive chemical reactions. This is advantageous as the direct use of electrons supplied from an electrode is an inherently cheap and environmentally friendly redox reagent. Additionally, electrochemistry allows for unique reaction pathways that would be difficult, if not impossible, to obtain via traditional chemical methodologies.</p><p dir="ltr">Herein, I discuss our work on advancing electrochemical synthesis for synthesizing high-nitrogen and energetic materials, which includes: An overview of potential reaction pathways toward developing promising high-nitrogen heterocyclic small molecules and polymers. Studies of the reaction efficiency of the decagram scale electrochemical production of useful energetic feedstocks, such as potassium dinitroethane. Novel azo bridged energetic materials produced via electrochemical amine oxidation reactions that were further utilized to prepare a series of energetic <i>N</i>-nitramines. Finally, a novel sequential electrochemical-photochemical methodology has been developed that has produced annulated heterocycles with promising pharmaceutical and energetic applications.</p>

Nanocrystalline cerium oxide thin films on metal and semiconductor substrates have been fabricated with a novel electrodeposition approach - anodic oxidation. X-ray diffraction analysis indicated that as-produced cerium oxide films are characteristic face-centered cubic fluorite structure with 5 ~ 20 nm crystal sizes. X-ray photoelectron spectroscopy study probes the non-stoichiometry property of as-produced films. Raman spectroscopy and Scanning Electron Microscopy have been applied to analyze the films as well. Deposition mode, current density, reaction temperature and pH have also been investigated and the deposition condition has been optimized for preferred oriented film formation: galvanostatic deposition with current density of -0.06 mA/cm2, T > 50oC and 7 < pH < 10. Generally, potentiostatic deposition results in random structured cerium oxide films. Sintering of potentiostatic deposited cerium oxide films leads to crystal growth and reach nearly full density at 1100oC. It is demonstrated that in-air heating favors the 1:2 stoichiometry of CeO2. Nanocrystalline cerium oxide powders (4 ~ 10 nm) have been produced with anodic electrochemical synthesis. X-ray diffraction and Raman spectroscopy were employed to investigate lattice expansion phenomenon related to the nanoscale cerium oxide particles. The pH of reaction solution plays an important role in electrochemical synthesis of cerium oxide films and powder. Cyclic voltammetry and rotation disk electrode voltammetry have been used to study the reaction mechanisms. The results indicate that the film deposition and powder formation follow different reaction schemes. Ce(III)-L complexation is a reversible process, Ce3+ at medium basic pH region (7~10) is electrochemically oxidized to and then CeO2 film is deposited on the substrate. CE mechanism is suggested to be involved in the formation of films, free Ce3+ species is coordinated with OH- at high basic pH region (>10) to Ce2O3 immediately prior to electrochemically oxidation Ce2O3 to CeO2. CeO2 / montmorillonite nanocomposites were electrochemically produced. X-ray diffraction and Raman spectroscopy illustrate the retaining of FCC structure for cerium oxide. Fourier Transform Infrared Spectroscopy and Differential Scanning Calorimetry of composites indicate the insertion of montmorillonite platelets into the structural matrix of cerium oxide. Sintering study of the nanocomposites demonstrates that low concentration of montmorillonite platelet coordination into cerium oxide matrix increases crystal growth rate whereas high concentration of montmoillonite in nanocomposites retards the increase of crystallite size during the densification process.

O glicerol, 1,2,3-propanotriol, é o principal subproduto da indústria do biodiesel, cerca de 10% em massa. Apesar das inúmeras aplicações que o glicerol tem na indústria, a oferta desse poliálcool, devido ao grande aumento da produção de biodiesel nos últimos anos, tem crescido tanto que o produto tem se acumulado nas usinas, levando a um desequilíbrio entre produção e consumo. Dessa forma, muita pesquisa vem sendo feita na tentativa de utilizar essa abundante, barata e não tóxica matéria prima como base para a obtenção de energia e outros produtos de maior valor agregado. Dentre os vários processos para a conversão do glicerol, a eletro-oxidação recebe atenção especial devido à sua versatilidade, simplicidade e baixo custo. Neste trabalho, utilizou-se a voltametria cíclica para a análise do comportamento eletroquímico do glicerol e dos possíveis produtos obtidos pela sua eletro-oxidação sobre diversos eletrodos e a influência de variáveis experimentais, tais como, solvente, eletrólito de suporte, concentrações de substrato e eletrólito de suporte, na atividade eletrocatalítica do sistema. As técnicas de eletroforese capilar, coulometria e voltametria cíclica foram utilizadas para a determinação da taxa de conversão e análise quantitativa do glicerol e dos produtos obtidos por meio de eletrólise exaustiva e como esses parâmetros são influenciados pelas variáveis experimentais. Além disso, é importante citar que o método analítico baseado na técnica de eletroforese capilar com detecção condutométrica sem contato foi desenvolvido e otimizado durante o projeto de mestrado e tem grande relevância para este trabalho / Glycerol, 1,2,3-propanetriol, is the main by-product of biodiesel industry, around 10% w/w. Despite of several glycerol applications in industry, the offer of this polyalcohol has increased so much in the last years that it has accumulated in the mills, leading to an unbalance between its production and consumption. Thus, a lot of research has been done trying to use this abundant, cheap and non-toxic raw material as the basis for energy production and synthesis of other more value-added compounds. Among the several conversion processes, the electrooxidation has drawn attention due to its versatility, simplicity and low cost. Cyclic voltammetry is used for analyzing the electrochemical behavior of glycerol and the possible electroconversion products on several electrodes, as well as the influence of experimental variables, such as, solvent, supporting electrolyte and its concentration, substrate concentration on the electrocatalytic activity of the system. Capillary electrophoresis, coulometry and cyclic voltammetry were used for determination of rate conversion and quantitative analyses of glycerol and the obtained products through bulk electrolysis and how these parameters are influenced by experimental conditions. Besides, it is noteworthy that the analytical method based on capillary electrophoresis technique with contactless conductometric detection was developed and optimized along this Master project and it has large relevance for this work.

Neste trabalho foram polimerizadas blendas e compósitos de polianilina (PAni), utilizando métodos químico e eletroquímico, sobre eletrodos de platina (Pt) e aço inoxidável (AISI-304), em diferentes meios aquosos. As blendas e compósitos de PAni foram preparados a partir de solução aquosa de H3PO4, contendo anilina e diferentes concentrações de carboximetilcelulose sódica (CMC) ou ácido dodecilbenzenosulfônico (DBSA). Para a formação dos filmes poliméricos, sobre ambos os substratos metálicos, a técnica de voltametria cíclica foi utilizada, tendo sido investigada a influência das concentrações de CMC e de DBSA nas características do processo de polimerização bem como, no material resultante. Por outro lado, na polimerização química, realizada a 20º.C e na presença de ((NH4)2S2O8), curvas potenciométricas e calorimétricas foram obtidas para auxiliar na caracterização das sínteses. Os materiais poliméricos foram caracterizados com o uso das técnicas de voltametria cíclica (resposta eletroquímica), espectroscopia de UV-Vis-NIR, espectroscopia de infravermelho, de medidas de condutividade por quatro pontos, microscopia eletrônica de varredura, espectroscopia dispersiva de energia de raios-x (EDX) e termogravimetria (TG). A partir dos resultados obtidos, foram observadas diferenças decorrentes da concentração de CMC, com influência tanto na velocidade de polimerização, quanto nas propriedades físicas e químicas de PAni-CMC. As interações entre PAni e CMC ocorrem por ligações de hidrogênio sendo a estrutura dos filmes PAni-CMC fortemente depende da concentração de CMC. Há significativas diferenças, tanto no processo de eletropolimerização de PAni-DBSA sobre Pt e AISI-304, quanto nas propriedades físicas e químicas dos polímeros. Estruturalmente, os filmes de PAni-DBSA eletropolimerizados sobre AISI-304 são mais porosos e apresentam maior eletroatividade, conseqüência da pré-camada de óxido formada durante a eletropolimerização. Mediante os ensaios de corrosão, foi verificado que os filmes de PAni-CMC aplicados sobre AISI-304 apresentam variação na composição após os ensaios de corrosão, enquanto que a proteção fornecida pelos filmes de PAni-DBSA depende da espessura dos mesmos. Ambos os filmes protegem efetivamente superfícies de aço inoxidável AISI-304 contra a corrosão e são alternativas extremamente viáveis quando comparados aos materiais convencionalmente utilizados. / In this work, polyaniline (PAni) blends and composites were obtained on platinum (Pt) and stainless steel (AISI-304) substrates. The effects of chemical and electrochemical syntheses were studied in different aqueous media. PAni blends and composites were prepared from aniline monomer-containing solutions of H3PO, that contained different concentrations of sodium carboxymethylcellulose (CMC) or dodecylbenzene sulphonic acid (DBSA). For the formation of polymeric films on Pt and steel AISI-304 electrodes, cyclic voltammetry was the technique employed and the effect of monomer, CMC and DBSA concentration on both the process characteristics and the resultant material were investigated. Chemical polymerization was performed at 20 &#61616;C, in the presence of an oxidizing agent [(NH4)2S2O8] and potentiometric and calorimetric curves were obtained, which permitted the characterization of the synthesis. The resultant polymeric materials were characterized by their electrochemical response, ultraviolet (UV-VIS) and infrared (IR) spectroscopies, conductivity measurements, scanning electronic microscopy (SEM), film composition analysis by energy dispersive ray-x spectroscopy (EDS) and thermogravimetric analysis (TG). From the polymer characterization, the results demonstrate the differences between the PAni polymers due to CMC concentration used in the polymerization, which influences both the polymerization rate and the physical and chemical properties of the PAni-CMC composite. The interaction between PAni and CMC occurs by hydrogen bonding, and the structure of the PAni-CMC film depends strongly on the CMC concentration. There are significant differences between the electropolymerization process of PAni-DBSA films on Pt and that on steel AISI-304, resulting in different the physical and chemical properties of the respective polymers. Structurally, the PAni-DBSA films electropolymerized on steel AISI-304 are more porous and present greater electroactivity due to an oxide layer formed during the electropolymerization. From corrosion assays, which involved performing open circuit potential and potentiodynamic curves in NaCl, the viability of application of PAni-CMC and PAni-DBSA films electropolymerized on steel AISI-304 electrodes was analyzed. For the PAni-CMC films on steel AISI-304 a significant change in the film composition occurred after the corrosion assays. On the other hand the corrosion protection of steel AISI-304 covered with PAni-DBSA is dependent on the film thickness. The electrochemical parameters extracted from the potentiodynamic curves demonstrate that both films protect stainless steel against corrosion. Furthermore, the corrosion studies show that PAni-CMC and PAni- DBSA films are viable alternatives to the conventionally used corrosion protection films.