Understanding electron-transfer (ET) processes in proteins is of fundamental importance. In a series of photophysical studies of well-behaved peptide model systems, it has become evident that the ET through peptide spacers is greatly influenced by the separation between the acceptor (A) and the donor (D), the nature of the peptide backbone, the amino acid sequence, and the resulting flexibility of the peptide conjugates. In particular, it was suggested in the literature that the presence of H-bonding will increase the rate of ET, and there is experimental evidence, mostly in proteins, to suggest that H-bonding indeed increases the rate of ET.<p>My aim was to develop a potential-assisted deposition method for ferrocene peptide disulfides onto gold surfaces and investigate the electrochemical properties of these films. We made use of two classes of Fc-peptides: acylic ferrocenoyl (Fc)-peptide disulfides and cyclo-1,1-Fc-peptide disulfides, allowing the preparation of tightly packed films of cyclic and acylic Fc-peptides on gold surfaces within 30 minutes. This is a significant benefit compared to the conventional soaking method of self-assembly requiring several days for the assembly of well-packed films. Such films exhibited considerably improved stability. This electrodeposition method should find wide-spread applications for the formation of tightly-packed films from disulfides. Our studies allowed a direct comparison of the electron transfer kinetics of cyclic and acyclic Fc-peptide disulfide systems. Our results showed faster ET kinetics for films prepared from cyclic Fc-peptide conjugates compared to the acyclic systems, presumably as a result of the enhanced rigidity of the Fc-peptide conjugates on the surface and/or an increase of the number of conductive peptide wires to the surface. Following the idea of peptide dynamics as a major contributor to the observed electron transfer rate in peptides and peptide conjugates, variable temperature electrochemical studies of Fc-peptide films were performed. An estimation of the reorganization energy associated with ferrocene/ferrocenium (Fc/Fc+) redox process allowed us to probe the role of peptide dynamics. Three counter-ions were tested, exhibiting different strengths of association with the Fc+ group (BF4- < ClO4- < PF6-) and the reorganization energies were evaluated in each case. The highest reorganization energy was obtained for the weakly interacting anion BF4-. Weakly interacting anions also showed significant broadness in the redox peaks and emergence of the second oxidation peak which is attributed to phase separation of the ferrocene group. Ferrocene agglomeration was not observed for any of the cyclic Fc-peptide conjugates but occurred for some of the acyclic systems. In particular, for acyclic Val and Leu containing Fc-peptide conjugates agglomeration were observed and was presumably caused by lateral interactions between the hydrophobic side-groups of the peptides. Further experiments involving the interaction of Fc-peptide films with alkali metal ions gave additional evidence that electron transfer is influenced significantly by peptide dynamics.

Since the diamond like carbon features include high hardness and high wear resistance, low friction coefficient, chemical inertness, high resistance, low dielectric constant, the IR Transparency and field emission. The process of Diamond carbon film was usually by CVD or PVD techniques. However, high substrate temperature or low deposition rate and the can not make large area of films leads to limit the applications of diamond like film. Electrodeposition method is an innovative method to prepare DLC film and it meets these demands such as: equipment cheap, high deposition rate and larger area coatings. In this paper, ITO substrate was used for electrodeposition the diamond-like carbon films and to evaluate the possibility for the large area of DLC films.For the process of electrical deposition, the electrolyte consists of acetic acid and DI water mixed in different proportions. The deposition process were conditioned as: electrolyte concentration between 0.01% and 0.8%; voltage from 2.1V to 50V; growth temperature in the range of 300C ~ 850C. In addition, by using the control variables method, the deposition parameters including voltage, deposition temperature and solution concentration of electrolyte were varied to evaluate the characteristics and quality of diamond-like carbon films. The n & k film analyzer (n & k Analyze), X ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM) were used to characterize the surface morphology, microstructure and compositional analysis. The reflectivity, transmittance, and refractive index of DLC Films were revealed by the n & k analyzer. Hence, the best conditions used for anti-reflective layer and projections Eopg can be achieved. For SEM analysis, the DLC film with uniformity surface structure can be found. Additionally, the current - time graph can be used to predict the properties of film varied with the applied voltage, percent of concentrations, growth temperature etc.. The microstructure of DLC film was investigated by the XPS measurement; the sp2 / sp3 ratio varies from the growth parameters changes. The hydrogen content of DLC films was obtained by FTIR measurements, the contents decrease as the operating voltage, electrolyte concentration and the substrate temperature increase. As for the DLC deposited on ITO glass as an anti-reflective layer, the experimental results showed that DLC film can reduce the reflectivity from 40% to 70%. Finally, the results obtained show a reasonable match for various measurements. T he characteristics of DLC films also shows that it very depends on the deposited parameters and the relationship beteen them was discussed in detailed. Some of the advance study will be investigated in future.

In this study, DLC thin films were electrodeposited at low DC potential using a mixture of acetic acid and DI water with different ratio. The parameters of DLC thin film deposition include the DC potential, deposition temperature, concentration of electrolyte solution, were correlated to the growth mechanism. The amount of nitrogen incorporated into DLC thin films were varied with the deposited temperature. The characteristics of DLC films by various measurements such as : the I-t curves of DLC film growth, SEM, AFM, FTIR, XPS, Raman and N&K spectroscopy, were investigated in detail. Experimental results showed that the surface roughness decreased, and sp3/sp2+sp3 value of DLC increased with the deposition temperature and deposition time. Optical properties showed that the refractive index, optical energy gap increased with the deposition temperature. For SEM cross-section measurement, it showed that the thickness of DLC films decreased due to the erosion process. However, the N-DLC films become graphitization. According to our study, we find that the surface morphology of the N-DLC films are homogeneous and compact. However, with the increase of the deposition temperature, the ratio of sp3-C-N bonds increase and the ratio of sp2-C-C bonds decrease, and these lead to the increase of refractive index and optical energy gap.

In this research, a low-cost template-based process has been developed to structure the surfaces of polymeric materials rendering them superhydrophobic. This biology-inspired approach was developed using results from the first part of this thesis: the first known detailed study of superhydrophobic aspen leaf surfaces. Aspen leaves, similar to lotus leaves, possess a dual-scale hierarchical surface structure consisting of micro-scale papillae covered by nano-scale wax crystals, and this surface structure was used as a blueprint in the structuring of templates. These distinctive surface features coupled with a hydrophobic surface chemistry is responsible for these leaves’ extreme non-wetting property. Non-wetting is further augmented by the unique high aspect ratio aspen leafstalk geometry. The slender leafstalks offer very little resistance to twisting and bending, which results in significant leaf movement in the slightest breeze, facilitating water droplet roll-off. The structured template surfaces, produced by sand blasting and chemical etching of electrodeposited nanocrystalline nickel sheets, resemble the negative of the superhydrophobic aspen leaf surfaces. Re-usable templates were subsequently employed in a hot embossing technique where they were pressed against softened polymers (polyethylene, polypropylene and polytetrafluoroethylene) thereby transferring their surface structures. The resulting pressed polymer surfaces exhibited features very similar to aspen leaf surfaces. This process increased the water contact angle for all pressed polymers to values above 150 degrees. Additionally, after pressing the water roll-off angle for all polymer surfaces dropped below 5 degrees. The effects of water surfactant concentration, water drop size and temperature on the wetting characteristics of the structured polymers were studied to indicate in which applications these functional surfaces could be most beneficial. Coupling this attractive superhydrophobic surface property with mechanical motion (shaking, bending, or vibrating) could result in superhydrophobic surfaces with superior non-wetting properties suitable for a wide range of applications.

In this research, a low-cost template-based process has been developed to structure the surfaces of polymeric materials rendering them superhydrophobic. This biology-inspired approach was developed using results from the first part of this thesis: the first known detailed study of superhydrophobic aspen leaf surfaces. Aspen leaves, similar to lotus leaves, possess a dual-scale hierarchical surface structure consisting of micro-scale papillae covered by nano-scale wax crystals, and this surface structure was used as a blueprint in the structuring of templates. These distinctive surface features coupled with a hydrophobic surface chemistry is responsible for these leaves’ extreme non-wetting property. Non-wetting is further augmented by the unique high aspect ratio aspen leafstalk geometry. The slender leafstalks offer very little resistance to twisting and bending, which results in significant leaf movement in the slightest breeze, facilitating water droplet roll-off. The structured template surfaces, produced by sand blasting and chemical etching of electrodeposited nanocrystalline nickel sheets, resemble the negative of the superhydrophobic aspen leaf surfaces. Re-usable templates were subsequently employed in a hot embossing technique where they were pressed against softened polymers (polyethylene, polypropylene and polytetrafluoroethylene) thereby transferring their surface structures. The resulting pressed polymer surfaces exhibited features very similar to aspen leaf surfaces. This process increased the water contact angle for all pressed polymers to values above 150 degrees. Additionally, after pressing the water roll-off angle for all polymer surfaces dropped below 5 degrees. The effects of water surfactant concentration, water drop size and temperature on the wetting characteristics of the structured polymers were studied to indicate in which applications these functional surfaces could be most beneficial. Coupling this attractive superhydrophobic surface property with mechanical motion (shaking, bending, or vibrating) could result in superhydrophobic surfaces with superior non-wetting properties suitable for a wide range of applications.

RuO2/carbon composites have attracted a lot of attention for use as supercapacitor electrodes due to their high power and energy capabilities. Methods for loading the RuO2 into the carbon include impregnation and electrochemical deposition. The first project involves impregnation of RuO2 nanoparticles into a mesoporous carbon powder. Structural changes of the RuO2 nanoparticles in the composite were induced by annealing at high temperatures, and X-ray diffraction (XRD) and X-ray absorption (XAS) were used to study the changes. In situ electrochemical-XAS experiments were also developed and performed to study the structural stability of the RuO2 nanoparticles in the composite as well as bulk RuO2•xH2O, with respect to changing potential. Preliminary work on the electrodeposition of RuO2•xH2O onto Au foil and carbon cloth was performed. An electrode with a high specific capacitance of the RuO2•xH2O component was achieved. However, further studies need to be performed to optimize the deposition solution.

Τα τελευταία χρόνια έχει αυξηθεί ιδιαίτερα το ενδιαφέρον για το υδρογόνο, καθώς η αξιοποίηση του θα μπορούσε να οδηγήσει σε μείωση της ανησυχίας για την εξάντληση των αποθεμάτων των ορυκτών κυρίως καυσίμων και της επιβάρυνσης του περιβάλλοντος. Ο προσανατολισμός προς την κατεύθυνση του υδρογόνου οφείλεται κυρίως στο υψηλό ενεργειακό περιεχόμενο του έναντι άλλων συμβατικών καυσίμων καθώς επίσης και στο γεγονός ότι κάνει "καθαρή" καύση αφού όταν καίγεται με οξυγόνο παράγει μόνο νερό και θερμότητα με αποτέλεσμα να μην ρυπαίνει το περιβάλλον. Πιο συγκεκριμένα, στη παρούσα εργασία αναλύεται η τεχνολογία παραγωγής υδρογόνου με τη μέθοδο της ηλεκτρόλυσης. Η ηλεκτρόλυση λαμβάνει χώρα σε ηλεκτρολυτικό κελί τύπου Hofmann. Ως ηλεκτρόδιο ανόδου χρησιμοποιήθηκε ανοξείδωτος χάλυβας StS304, ενώ ως ηλεκτρόδιο καθόδου υπόστρωμα χαλκού πάνω στο οποίο εναποτέθηκαν με τη μέθοδο της ηλεκτροχημικής εναπόθεσης, λεπτά υμένια μεταβατικών μετάλλων με βάση το νικέλιο. Τα υμένια που παρασκευάστηκαν ήταν NiFe, NiFeZn, NiCoZn, NiMoFe, NiZn και NiMoZn. Κύριος στόχος της εργασίας ήταν η μελέτη των ηλεκτροκαταλυτικών ιδιοτήτων των παραπάνω υμενίων ως προς την παραγωγή υδρογόνου. Αρχικά μελετήθηκαν τα υμένια σε πραγματικές συνθήκες ηλεκτρόλυσης, μετρώντας την παραγωγή υδρογόνου για συγκεκριμένες πάντα συνθήκες. Στη συνέχεια έγιναν μετρήσεις υπερδυναμικού παραγωγής υδρογόνου και από τα δεδομένα αυτά και με τη βοήθεια των διαγραμμάτων Tafel υπολογίστηκαν οι ηλεκτροκαταλυτικοί συντελεστές, όπως η πυκνότητα ρεύματος ανταλλαγής και η κλίση Tafel. Τέλος, για μια πιο ολοκληρωμένη εικόνα για την επίδραση των συνθηκών της ηλεκτροχημικής εναπόθεσης στην μορφολογία της επιφάνειας των λεπτών υμενίων. πραγματοποιήθηκαν μετρήσεις σε ηλεκτρονικό μικροσκόπιο σάρωσης (SEM). / Recently the interest in hydrogen has increased as the utilization could lead to reduced concern about depletion of fossil fuels . The increased interest for hydrogen is mainly due to its high energy content compared to other fossil fuels, as well as the fact that it is a completely clean burning fuel; its only product is water. In the present study hydrogen production by electrolysis is analyzed. Electrolysis takes place in type Hofmann electrolytic cell. As anode electrode stainless steel StS304 was used. As cathode electrode copper substrate was used; in particular we have deposited films of the transition metal Ni on copper substrates. The alloys we fabricated were NiFe, NiFeZn, NiCoZn, NiMoFe, NiZn and NiMoZn. The main objective of this work was to study the electrocatalytic properties of these films for hydrogen production. At first we studied the electrocatalytic properties of the thin film alloys during the electrolytic production process using the same conditions every time. Subsequently, we measured the hydrogen production overvoltage, and using these data, we constructed Tafel diagrams and calculate Electrocatalytic coefficients sush as: exchange current density and Tafel slope. Finally SEM , gave us a complete picture of the effect of the electrochemical deposition conditions on the morphology of the surface of thin films.

>Magister Scientiae - MSc / A study on carbon paste electrode (CPE) materials containing 1-methyl-3-octylimidazolium bis (trifluoromethylsulfonyl) imide [MOIM[Tƒ2N] – a hydrophobic room temperature ionic liquid (IL) - is reported. CPEs with (a) the IL as the only binder (ILCPE) and (b) 1:1 (v/v) IL: paraffin mixture as the binder (ILPCPE) were prepared, characterized, and applied to the electrodeposition of films of multivalent transition metal oxides (MV-TMO) from five precursor ions (Fe2+, Mn2+, Cu2+, Co2+, Ce4+) in aq. KCl. Cyclic voltammetry (CV) showed a potential window of +1.5 V to -1.8 V regardless of the electrode type, including the traditional paraffin CP electrode (PCPE). However, the IL increased the background current by 100-folds relative to paraffin. The electrochemical impedance spectroscopy (EIS) of ILPCPE in aq. KCl (0.1M) revealed two phase angle maxima in contrast with the single maxima for PCPE and ILCP. The study also included the CV and EIS investigation of the electrode kinetics of the Fe(CN)6 3-/4 redox system at these electrodes. The electrodeposition of Fe2+, Co2+, and Mn2+ possibly in the form of the MV-TMOs FexOy, CoxOy, and MnxOy, respectively, onto the electrodes was confirmed by the observation of new and stable cathodic and anodic peaks in a fresh precursor ion –free medium. CVs of H2O2 as a redox probe supported the same conclusions. Both ATR-FTIR spectra and SEM image of surface samples confirmed the formation of electrodeposited films. This study demonstrated that the use of this hydrophobic IL alone or in combination with paraffin as a binder gives viable alternative CPE materials with better performance for the electrodeposition of MV-TMOs films than the paraffin CPE. Thus, in combination with the easy preparation methods and physical “morpheability” in to any shape, these CPEs are potentially more useful in electrochemical technologies based on high surface-area MV-TMO films in general, and MnxOy films in particular.

Made available in DSpace on 2014-06-11T19:32:11Z (GMT). No. of bitstreams: 0 Previous issue date: 2011-10-21Bitstream added on 2014-06-13T20:42:54Z : No. of bitstreams: 1 baptista_jaa_dr_araiq.pdf: 3396992 bytes, checksum: fc53db41a4c7db199456bac2e1fe3e67 (MD5) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / Neste trabalho estudou-se a permeação de hidrogênio no aço CFF durante a eletrodeposição de zinco em diferentes soluções de eletrodeposição, densidade de corrente e o tempo. Estes estudos foram feitos empregando-se as técnicas de voltametria cíclica, cronoamperometria do hidrogênio permeado em um eletrodo bipolar, microscopias óticas e de varredura eletrônica. As voltametrias cíclicas foram feitas para analisar o comportamento do aço diante das soluções empregadas para a eletrodeposição e para determinar o comportamento dos depósitos de zinco formados em diferentes banhos em solução tampão borato (pH 8,4). Observou-se que as soluções de eletrodeposição de zinco que continham citrato de sódio (NaCit), os voltamogramas cíclicos não mostraram a região de oxidação do zinco eletrodepositado e respectiva oxidação, indicando que o íon zinco está na forma de um complexo estável, o que dificulta a deposição de zinco, tornando o depósito mais compacto. A maioria dos voltamogramas cíclicos dos revestimentos de zinco sobre aço CFF mostrou a presença de um pico em torno de -1,0 V, que foi relacionado à deposição do zinco. Em potenciais mais positivos após a deposição do zinco ocorre oxidação da superfície formando um óxido que bloqueia a superfície do eletrodo, porém em este fenômeno não é observado após a formação do depósito para soluções que contém citrato de sódio (NaCit). As imagens de MEV dos depósitos mostraram diferentes morfologias dos depósitos de zinco nos banhos estudados, que dependem da corrente aplicada e do tempo de deposição. A composição do banho também influencia na morfologia dos depósitos obtidos, sendo que, entre as soluções estudadas, a que continha somente citrato de sódio, sulfato de zinco e cloreto de potássio em sua composição formaram depósitos mais compactos... / In this work, the hydrogen permeation into CFF steel, during the zinc electrodeposition, was studied using different baths, current densities and deposition time. These studies were carried out by employing the following techniques: cyclic voltammetry, chronoamperometry of the permeated hydrogen in a bipolar electrode, optical and electronic microscopy. The cyclic voltammetry was conducted in order to analyze the steel behavior with relation to the utilized solutions for its electrodeposition and also to determine the behavior of the formed zinc deposits in different baths in borate buffer solution (pH 8.4). It was observed that cyclic voltammograms for the solutions of zinc electrodeposition containing sodium citrate (NaCit) did not show the region corresponding to the oxidation of electrodeposited zinc, indicating that the zinc ion is forming a stable complex. In this situation, the complex hinders the zinc deposition and therefore the deposit becomes more compact. Most of cyclic voltammograms for zinc coatings into CFF steel exhibited the presence of a peak at about -1.0 V, which is related to the zinc deposition. At more positive potentials after the zinc deposition, it takes place surface oxidation, forming an oxide that blocks the electrode surface. However, this phenomenon is not noticed after the deposit formation for solutions containing sodium citrate (NaCit). The SEM images of the zinc deposits presented different morphologies depending on the bath, applied current density and deposition time. The bath composition also influences on the obtained deposits morphology, where the bath containing only sodium citrate, zinc sulfate and potassium chloride formed more compact, adherent and less rough deposits. The growth and formation of the zinc coatings were observed in situ by optical microscopy, showing that the deposition curren... (Complete abstract click electronic access below)

Made available in DSpace on 2014-06-11T19:35:06Z (GMT). No. of bitstreams: 0 Previous issue date: 2011-04-19Bitstream added on 2014-06-13T19:05:17Z : No. of bitstreams: 1 ribas_gcb_dr_araiq.pdf: 3555031 bytes, checksum: 870a15eca5c7dcd996e81e1d56ce8831 (MD5) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / Os metais nobres Pt, Rh e Ir e suas ligas apresentam diversas aplicações tecnológicas. O Hg pode ser considerado o principal contaminante dos metais nobres e suas ligas binárias e terciárias, por apresentar alta reatividade e uma ação corrosiva sobre os mesmo. Devido a isso, o objetivo deste trabalho foi estudar as reações em estado sólido das ligas Pt-6% Rh e Pt-10% Ir na presença e ausência de Hg, empregando técnicnas eletroquímicas e termogravimétricas. O preparo dos sistemas para os estudos eletroquímicos e de termogravimetria (TG/DTG) constituiu em fazer eletrodeposições de Hg no substrato metálico, com o auxílio de voltametria cíclica, gerando um filme de Hg e compostos intermetálicos sobre a superfície da lâmina. A partir desses resultados, foi possível evidenciar o ataque efetivo do mercúrio sobre o substrato, e a formação de compostos intermetálicos (PtHg, PtHg2, RhHg2 e PtHg4), que foram caracterizados com o auxílio das seguintes técnicas de análise de superfície: microanálise por EDX, mapeamento dos elementos, obtenção de imagens de MEV e difratometria de raios X (XRD). Estas análises de superfície revelaram também, uma distribuição homogênea do Hg, e a presença de um filme de intermetálicos sobre a superfície do substrato. A comparação entre os sistemas Pt-10% Ir-Hg e Pt-6% Rh-Hg sugere uma menor reatividade do substrato de Ir quando são empregadas as mesmas condições experimentais / The noble metals Pt, Rh and Ir and its alloys have many technological applications. Mercury can be considered a major contaminant of noble metals and their binary and tertiary alloys due to high reactivity and a corrosive action on the same. Because of this, the objective was to study the solid state reactions of the alloys Pt-6% Rh and Pt-10% Ir in the presence and absence of mercury, using electrochemical and thermogravimmetry techniques. The preparation of systems for electrochemical and thermogravimmetry (TG/DTG) studies consisted to make electrodepositions of mercury in the metallic substrate, using cyclic voltammetry techniques to generate a film of mercury and intermetallic compounds. From these studies, it was possible to show the actual attack of mercury on the substrate, and the formation of intermetallic compounds (PtHg, PtHg2, RhHg2 and PtHg4), which were characterized using these analysis of surface techniques: EDX microanalysis, mapping of the elements, scanning electronic microscopy and X-ray diffraction (XRD).These analysis also revealed a homogeneous distribution of mercury, and the presence of an film of intermetallic compounds on the surface of the substrate. The comparison between the systems Pt-10% Ir-Hg and Pt-6% Rh-Hg suggesting a lower reactivity of Ir are used when the same experimental conditions