Orientador: Devaney Ribeiro do Carmo / Resumo: O presente trabalho descreve a preparação de materiais porosos (MCM-41 e Zeólita FAU) inorganofuncionalizados com Titânio e Zircônio e subsequente modificação química com hexacianoferrato de níquel. Os materiais preparados foram caracterizados empregando diferentes técnicas: Espectroscopia na Região do Infravermelho por transformada de Fourier (FTIR), Ressonância Magnética Nuclear (RMN), Difração de Raios-X (DRX), Microscopia Eletrônica de Varredura (MEV), Espectroscopia de Energia Dispersiva de Raios-X (EDX), Análise Termogravimétrica (TGA), Porosidade e Área superficial. Após a obtenção dos materias (MTiNiH, MZrNiH, ZTiNiH e ZZrNiH), realizou-se um estudo sistemático sobre o comportamento voltamétrico desses materiais, empregando a técnica de Voltametria Cíclica (VC) e eletrodos de pasta de grafite. O voltamograma cíclico dos materiais MTiNiH e ZTiNiH exibiram um par redox bem definido com Eθ’= 0,49 V e os eletrodos de pasta de grafite modificados com MZrNiH e ZZrNiH exibiram um par redox com Eθ’= 0,50 V, atribuídos ao processo Fe(II)/Fe(III) em presença de níquel (II). Os eletrodos de pasta de grafite modificados com os materiais citados anteriormente mostraram-se sensível a concentrações de isoniazida e sulfito, sendo que apresentaram melhores desempenhos na eletro-oxidação catalítica da isoniazida. Após os testes de eletro-oxidação catalítica dessas substâncias, realizou-se uma investigação da influência dos principais interferentes, de forma que a interferência observad... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: The present work describes the preparation of porous materials (MCM-41 and FAU Zeolite) inorganofunctionalized with Titanium and Zirconium and subsequent chemical modification with nickel hexacyanoferrate. The prepared materials were characterized using different techniques: Fourier Transform Infrared Spectroscopy (FTIR), Nuclear Magnetic Resonance (NMR), X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM), Energy Dispersive X-Ray Spectroscopy (EDX), Thermogravimetric Analysis (TGA), Porosity and Surface Area. After obtaining the materials (MTiNiH, MZrNiH, ZTiNiH and ZZrNiH), a systematic study on the voltammetric behavior of these materials was performed using the Cyclic Voltammetry technique (CV) and modified graphite paste electrodes. The cyclic voltammogram of the MTiNiH and ZTiNiH materials exhibited a well-defined redox pair with Eθ’ = 0.49 V whereas the MZrNiH and ZZrNiH modified graphite paste electrodes exhibited a redox pair with Eθ’ = 0.50 V, all of them being assigned to the redox process Fe(II)/Fe(III) in the presence of nickel (II). The graphite paste electrodes modified with the aforementioned materials were sensitive to isoniazid and sulfite concentrations, and showed greater performance in the catalytic electrooxidation of isoniazid. After the catalytic electro-oxidation tests of these substances, the influence of the main interferents was investigated and so the observed interference was not significant for isoniazid. Recovery of these substances fro... (Complete abstract click electronic access below) / Doutor

Made available in DSpace on 2016-08-19T12:56:40Z (GMT). No. of bitstreams: 1 DISSERTACAO WENDELL.pdf: 1449569 bytes, checksum: 3293ccaefc405f2d45f32533547f901d (MD5) Previous issue date: 2012-07-05 / A ruthenium (III) hexacyanoferrate film was anchored with Nafion® on the surface of a glassy carbon electrode and tested in Britton-Robinson buffer ionic strength of 0.1 mol L-1 and pH = 1.8 at room temperature. The cyclic voltammograms of the electrode with the film showed four pair peaks with a surface-confined characteristic and they also indicated that the film is strongly dependent on the solution pH. The ruthenium (III) hexacyanoferrate film showed an excellent electrocatalytic activity toward the oxidation of hydrazine. The electrocatalytic oxidation of hydrazine was studied by cyclic voltammetry, rotating disk electrode voltammetry and chronoamperometry techniques. It has been observed that the oxidation of hydrazine to nitrogen occurs at a potential where oxidation is not observed at the bare glassy carbon electrode. The overall number of electrons involved in the catalytic oxidation of hydrazine was determined by cyclic voltammetry and rotating disk electrode experiments. A Tafel plots indicated a one-electron charge transfer process to be the rate-limiting step and the overall number of electrons involved in the catalytic oxidation of hydrazine was found to be four. It has been shown that the catalytic oxidation of hydrazine obeys fist-order kinetics with respect to hydrazine concentration. The diffusion coefficient of hydrazine was also estimated using chronoamperometry, presenting a value of 1,2 x 10-5 cm2 s-1. / Um filme de hexacianoferrato de rutênio (III) foi ancorado com Nafion® na superfície de um eletrodo de carbono vítreo e testado em tampão Britton- Robinson com força iônica de 0,1 mol L-1e pH = 1,8 à temperatura ambiente. Voltamogramas cíclicos do eletrodo com o filme mostraram quatro pares de picos com características de espécies confinadas na superfície do eletrodo. A resposta eletroquímica do filme de hexacianoferrato de rutênio (III) apresentou alta dependência do pH da solução e excelente atividade eletrocatalítica para a oxidação de hidrazina. O estudo eletrocatalítico foi realizado por voltametria cíclica, eletrodo de disco rotatório e cronoamperometria. Foi observado que a oxidação de hidrazina a nitrogênio acontece em uma região de potencial onde a oxidação não é observada para o eletrodo de carbono vítreo sem o filme de hexacianoferrato de rutênio (III). O número total de elétrons envolvidos na oxidação catalítica da hidrazina foi determinado por experimentos de voltametria cíclica e eletrodo de disco rotatório. Diagramas de Tafel indicaram que a reação de oxidação eletrocatalítica da hidrazina envolve um número total de quatro elétrons, sendo que um elétron é envolvido no processo de transferência de carga na etapa determinante da reação. Os resultados indicaram que a oxidação eletrocatalítica de hidrazina obedece a uma cinética de primeira ordem com relação à concentração da hidrazina. O coeficiente difusional da hidrazina foi também estimado usando cronoamperometria apresentando um valor de 1,2 x 10-5 cm2 s-1.

Prussian blue (PB) and Prussian blue analogues (PBAs) are compounds with potential applications in a large variety of fields such as gas storage, poison antidotes, electrochromism, electrochemistry and molecular magnets. The compounds are easy to synthesize, cheap, environmentally friendly and have been pursued for both fundamental research and industrial purposes. Despite the multifunctionality of PB and PBAs, they have complicated compositions, which are largely dependent on the synthesis methods and storage conditions. Thus, performing investigations on such compounds with defined composition, stoichiometry and crystal structure is essential. This thesis has focused on synthesis and detailed structure characterization of copper hexacyanoferrate (CuHCF) via X-ray powder diffraction (XRPD), neutron powder diffraction (NPD), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), inductively coupled plasma-optical emission spectroscopy (ICP-OES), scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS), Mössbauer spectroscopy, extended X-ray absorption fine structure (EXAFS), infrared (IR) and Raman techniques. In addition, kinetics of thermal dehydration process, CO2 adsorption and CO2 adsorption kinetics were investigated. Moreover, in operando synchrotron X-ray diffraction experiments were performed to gain insight into the structure-electrochemistry relationships in an aqueous CuHCF/Zn battery during operation. / <p>At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 4: Manuscript. Paper 5: Manuscript.</p>

Electrical double-layer formed at the interface between an electrode and an electrolyte has been a topic of innumerable studies. The electrical interface plays a crucial role in kinetics, mechanisms and applications in variety of electrochemical reactions. The electrical double-layer and electron-transfer reactions lead to many important applications of electrochemistry, which include energy storage devices, namely, batteries, fuel cells and supercapacitors. Electrochemical supercapacitors can withstand to higher power than batteries and deliver higher energy than the conventional electrostatic and electrolytic capacitors. A supercapacitor can be used as an auxiliary energy device along with a primary source such as a battery or a fuel cell for the purpose of power enhancement in short pulse applications. Among the various materials studied for electrochemical supercapacitors, carboneous materials, metal oxides and conducting polymers received attention. Among carboneous materials, various forms of carbon such as powders, woven cloths, felts, fibers, nanotubes etc., are frequently studied for electrochemical supercapacitors. Low cost, high porosity, higher surface area, high abundance and well established electrode fabrication technologies are the attractive features for using carboneous materials. However, specific capacitance (SC) of these materials is rather low. These electrodes store charge by electrostatic charge separation at the electrode/electrolyte interface. Electronically conducting polymers are interesting class of materials studied for supercapacitor application because of the following merits: high electronic conductivity, environmental friendliness, ease of preparation and fabrication, high stability, high capacitance and low cost. Polyaniline (PANI), polypyrrole and polythiophene are studied in this category. Transition metal oxides have attracted considerable attention as electrode materials for supercapacitors because of the following merits: variable oxidation state, good chemical and electrochemical stability, ease of preparation and handling. Hydrated RuO2 prepared by sol-gel process at low temperature has a specific capacitance as high as 720 F g-1 due to solid state pseudo faradaic reaction. However, high cost, low porosity and toxic nature limit commercialization of supercapacitors using this material. MnO2 is attractive as it is cheap, environmentally benign, its resources are abundant in nature and also it is widely used as a cathode material in batteries. An early study on capacitance behaviour of MnO2 was reported by Lee and Goodenough. Amorphous hydrous MnO2 synthesized by co-precipitation method exhibited rectangular cyclic voltammogram in various aqueous alkali salt solutions. A specific capacitance of 200 F g-1 was reported. Following this report, several reports appeared on capacitance characteristics of MnO2. According to the charge-storage mechanism reported, a specific capacitance of 1370 F g-1 is expected from MnO2. However, this value can be obtained in practice only when the mass of MnO2 is at the level of a few micrograms per cm2 area. At such a low thickness range, the utilization of the active material is high. As thin layers of MnO2 are uneconomical for practical capacitors, studies with a mass range of 0.4-0.5 mg cm-2 have been extensively reported. At this mass range, a maximum specific capacitance of about 240 F g-1 has been obtained. With an increase in mass per unit area, the specific capacitance of MnO2 decreases. The problem associated with low values of specific capacitance of thick layers of MnO2 is the following. The MnO2 deposits or coatings generally do not possess high porosity and the electrolyte cannot permeate into the coating. Only the outer layer of the electrode is exposed to the electrolyte. Consequently, the electrochemical utilization of the material decreases with an increase in thickness. Nevertheless, utilization of thick layers of the active materials is preferable for obtaining capacitance as high as possible in a given volume and area of the electrodes. Indeed, it would be ideal if specific capacitance of MnO2 is improved from its presently reported value of 240 F g-1 to a value equivalent to that of RuO2.xH2O, namely, 720 F g-1. In view of this, attempts are made to enhance specific capacitance of MnO2 by electrochemical deposition in presence of surfactants. Nanostructured MnO2 synthesized by inverse microemulsion route is also studied for electrochemical supercapacitors. The effect of crystallographic structure of MnO2 on the capacitance properties, studies on electrochemical deposition of MnO2 in acidic and neutral medium using electrochemical quartz crystal microbalance and capacitance characteristics of MnO2-polyaniline composites are also described in the thesis. Chapter 1 briefly discusses the importance of electrochemistry in energy storage and conversion, basics of electrochemical power sources, importance of MnO2, different synthetic procedures for MnO2 and its applications in energy storage and conversion in particular for electrochemical supercapacitors. Chapter 2 provides the experimental procedures and methodologies used for the studies reported in the thesis. In chapter 3, the effect of surface active agents, namely, sodium dodecyl sulphate (SDS) and Triton X-100 added to the electrolyte during electrodeposition of MnO2 on Ni substrate on capacitance properties is presented. Electrocrystallization studies show that MnO2 nucleates instantaneously under diffusion control and grows in three dimensions. The potentiodynamically prepared oxide provides higher specific capacitance than the potentiostatically and galvanostatically prepared oxides. Specific capacitance values of 310 and 355 F g-1 obtained for MnO2 electrodeposited in the presence of 100 mM SDS and 10 mM Triton X-100 are higher than the oxide electrodeposited in the absence of surfactants. Surfactant molecules adsorbed at the electrode/electrolyte interface alters structure of double-layer and kinetics of electrodeposition. Smaller particle size, greater porosity, higher specific surface area and higher efficiency of material utilization are the factors responsible for obtaining higher specific capacitance. Extended cycle-life studies indicate that the superior performance of MnO2 due to surfactants is present throughout the cycle-life tested. Chapter 4 pertains to electrochemical supercapacitor studies on nanostructured α-MnO2 synthesized by inverse microemulsion method and the effect of annealing. As synthesized nanoparticles of MnO2 was found to be in α-crystallographic structure with particles less than 50 nm size. Nanoparticles exhibited rectangular cyclic voltammograms between 0 and 1 V vs. SCE in aqueous 0.1 M Na2SO4 at sweep rates up to 100 mV s-1 due to the short diffusion path length. On annealing at different temperatures, a mixture of nanoparticles and nanorods with varying dimension is noticed. Specific capacitance of 297 F g-1 obtained during initial cycling decreases gradually on extended cycling. The capacitance loss is attributed to the increase in the resistance for intercalation/deintercalation of alkali cations into/from MnO2 lattice. MnO2 crystallizes into several crystallographic structures, namely, α-, β-, γ-, δ- and λ-structures. As these structures differ in the way MnO6 octahedra are interlinked, they possess tunnels or inter-layers with gaps of different magnitudes. Because capacitance properties are due to intercalation/deintercalation of protons or cations in MnO2, only some crystallographic structures, which possess sufficient gap to accommodate these ions, are expected to be useful for capacitance studies. The effect of crystal structure of MnO2 on its electrochemical capacitance properties is also included in chapter 4. Specific capacitance of MnO2 is found to depend strongly on the crystallographic structure, and it decreases in the following order: α ≅ δ > γ > λ > β. A specific capacitance value of 240 F g-1 is obtained for α-MnO2, whereas it is 9 F g-1 for β-MnO2. A wide (~ 4.6 Å) tunnel size and large surface area of α-MnO2 are ascribed as favorable factors for its high specific capacitance. A large interlayer separation (~7 Å) also facilitates insertion of cations in δ-MnO2 resulting in SC close to 236 F g-1. A narrow tunnel size (1.89 Å) does not allow intercalation of cations into β-MnO2. As a result, it provides very small SC. In Chapter 5, capacitance characteristics of PANI synthesized using (NH4)2S2O8, nanostructured MnO2 (α- and γ-form) and also PANI-MnO2 composites are presented. Morphology of PANI synthesized resembles the morphology of the MnO2 used as the oxidant. Electrochemical capacitance properties of PANI and composites are studied in a mixed electrolyte of 0.1 M HClO4 and 0.3 M NaClO4 between 0 and 0.75 V vs. SCE. Specific capacitance of 394 F g-1 is obtained for PANI synthesized using γ-MnO2. Chapter 6 describes the electrocatalytic behaviour of Mn3[Fe(CN)6]2 synthesized by ion-exchange reaction between MnSO4 and K3[Fe(CN)6] and the effect of annealing on its electrochemical capacitance properties. As prepared Mn3[Fe(CN)6]2 and also the sample heated at 100 oC exhibit redox couple in 0.1 M Na2SO4 electrolyte, corresponding to Fe(CN)64-/Fe(CN)63- present in the matrix. Mn3[Fe(CN)6]2 samples annealed at 150 oC and above decompose to oxides of manganese and iron, and hence exhibit capacitance characteristics in 0.1 M Na2SO4 electrolyte. A maximum specific capacitance of 129 F g-1 is obtained for Mn3[Fe(CN)6]2 annealed at 300 oC. Electrochemical quartz crystal microbalance (EQCM) investigations of kinetics of electrodeposition of MnO2 in acidic and neutral media, and capacitance behaviour are presented in chapter 7. Oxidation of Mn2+ to MnO2 is characterized by an anodic cyclic voltammetric peak both in acidic and neutral media. During the reverse sweep, however, reduction of MnO2 into Mn2+ occurs in two steps in the acidic medium and in a single step in the neutral medium. From EQCM data of mass variation during cycling, it is observed that the rate of electrodeposition of MnO2 is higher in the neutral medium than in the acidic medium. Specific capacitance of MnO2 deposited from the neutral medium is higher than that deposited from acidic medium owing to different crystallographic structures. Reversible insertion/deinsertion of hydrogen in to the layers of δ-MnO2 is observed in hydrogen evolution region. Details of the above studies are described in the thesis.

Submitted by KELY SILVEIRA BONFIM null (kely_bonfim@hotmail.com) on 2018-04-03T11:29:36Z No. of bitstreams: 1 DISSERTAÇÃO Kely S Bonfim REPOSITÓRIO.pdf: 21420988 bytes, checksum: 96c7e94b56ac3b3bb0da89a1467d1409 (MD5) / Approved for entry into archive by Cristina Alexandra de Godoy null (cristina@adm.feis.unesp.br) on 2018-04-03T13:03:20Z (GMT) No. of bitstreams: 1 bonfim_ks_me_ilha.pdf: 21420988 bytes, checksum: 96c7e94b56ac3b3bb0da89a1467d1409 (MD5) / Made available in DSpace on 2018-04-03T13:03:20Z (GMT). No. of bitstreams: 1 bonfim_ks_me_ilha.pdf: 21420988 bytes, checksum: 96c7e94b56ac3b3bb0da89a1467d1409 (MD5) Previous issue date: 2018-03-02 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / O óxido de grafeno (OG) pertence a uma nova classe de materiais cristalinos bidimensionais que tem se destacado no campo científico inter e multidisciplinar, devido a propriedades especiais, que possibilitam a sua aplicação em nanomembranas, supercapacitores, biossensores, liberação controlada de fármacos; entre outros. A sua estrutura consiste em uma camada individual de grafeno ornamentada com grupos funcionais oxigenados que permitem que o óxido de grafeno seja modificado quimicamente com diversas moléculas, átomos ou íons metálicos, podendo resultar em um excelente sensor eletroquímico. Em vista disso, o presente trabalho descreve a modificação química do óxido de grafeno com o dendrímero PAMAM G.0 (OGP) e posterior reação com hexacianoferrato (II) e (III) de potássio e nitrato de cério (III) para aplicação eletroanalítica. Os materiais híbridos formados (OGPH(II)Ce e OGPH(III)Ce) foram caracterizados por diferentes técnicas, tais como: Espectroscopia de Fotoelétrons Excitados por Raios-X (XPS), Espectroscopia na Região do Infravermelho com Transformada de Fourier (FTIR), Espectroscopia de Energia Dispersiva de Raios-X (EDX), Microscopia Eletrônica de varredura (MEV) e Difração de Raios-X (DRX). Como aplicação eletroanalítica, os mesmos foram empregados com sucesso na eletro-oxidação catalítica de Ácido Ascórbico e Dopamina, utilizando para tal finalidade o eletrodo de pasta de grafite e a técnica de voltametria cíclica. O eletrodo de pasta de grafite modificado com OGPH(II)Ce apresentou duas regiões lineares para a eletro-oxidação catalítica do Ácido Ascórbico, sendo que a primeira região apresentou um limite de detecção (LD) de 2,14×10-7 mol L-1 e sensibilidade amperométrica (S) de 43,68 mA/mol L-1; para a segunda região, o LD foi de 2,29×10-6 mol L-1 e a S = 12,73 mA/mol L-1. O mesmo material também apresentou resposta favorável para a Dopamina, com LD = 4,09×10-7 mol L-1 e S = 195,28 mA/mol L-1 para a primeira região; LD = 1,39×10-6 mol L-1 e S = 25,10 mA/mol L-1 para a segunda região. Os resultados obtidos para o segundo material (OGPH(III)Ce) para detecção de Ácido Ascórbico, apresentaram LD = 1,37×10-7 mol L-1 e S = 78,43 mA/mol L-1 para a primeira região, LD = 4,10×10-6 mol L-1 e S = 16,55 mA/mol L-1 para a segunda região; além da detecção de Dopamina com LD = 6,62×10-7 mol L-1 e S = 85,26 mA/mol L-1. Desta forma, os materiais híbridos formados, incluem-se no rol dos materiais obtidos como potenciais candidatos para a construção de sensores eletroquímicos na detecção de Ácido Ascórbico e Dopamina. / Graphene oxide (GO) belongs to a new class of two-dimensional crystalline materials that has excelled in the inter and multidisciplinar scientific field due to special properties that enables its apllication in nanomembranes, supercapacitors, biosensors, drug releaser; among others. Its strutcture consists on an individual layer of ornate graphene with oxygenated functional groups that allow the graphene oxide to be chemically modified with several molecules, atoms or metallic ions, which can result in an excellent electrochemical sensor. Therefore, the present work describes the chemical modification of the graphene oxide with the PAMAM G.0 (GOP) dendrimer and subsequent reaction with potassium hexacyanoferrate (II) and (III) and cerium nitrate (III) for electroanalytical application. The hybrid materials formed (GOPH(II)Ce and GOPH(III)Ce) were characterized by different techniques, such as: X Rays Photoelectron Spectroscopy (XPS), Fourier Transform Infrared Spectroscopy (FTIR), Scanning Electron Microscopy (SEM), Energy Dispersive X- rays Spectroscopy (EDS) and X-ray diffraction (XRD). As an electroanalytical application, the same were successfully used in the catalytic electro-oxidation of Ascorbic Acid and Dopamine, using for this purpose the graphite paste electrode and the cyclic voltammetry technique. The graphite paste electrode modified with GOPH(II)Ce presented two linear regions for the catalytic electro-oxidation of Ascorbic Acid, wherein the first region presented a detection limit (DL) of 2,14×10-7 mol L-1 and amperometric sensitivity (S) of 43,68 mA/mol L-1; for the second region the DL was of 2,29×10-6 mol L-1 and the S = 12,73 mA/mol L-1. The same material also presented a favorable response for Dopamine, with DL= 4,09×10-7 mol L-1 and S = 195,28 mA/mol L-1 for the first region; DL = 1,39×10-6 mol L-1 and S = 25,10 mA/mol L-1 for the second region. The results obtained for the second material (GOPH(III)Ce) for ascorbic acid detection, presented DL= 1,37×10-7 mol L-1 and S = 78,43 mA/mol L-1 for the first region, DL = 4,10×10-6 mol L-1 and S = 16,55 mA/mol L-1 for the second region; besides of Dopamine detection with DL = 6,62×10-7 mol L-1 and S = 85,26 mA/mol L-1. In this way, the hybrid materials formed are included in the list of materials obtained as potential candidates for the construction of electrochemical sensors in the ascorbic acid and dopamine detection.

Orientador: Devaney Ribeiro do Carmo / Resumo: O óxido de grafeno (OG) pertence a uma nova classe de materiais cristalinos bidimensionais que tem se destacado no campo científico inter e multidisciplinar, devido a propriedades especiais, que possibilitam a sua aplicação em nanomembranas, supercapacitores, biossensores, liberação controlada de fármacos; entre outros. A sua estrutura consiste em uma camada individual de grafeno ornamentada com grupos funcionais oxigenados que permitem que o óxido de grafeno seja modificado quimicamente com diversas moléculas, átomos ou íons metálicos, podendo resultar em um excelente sensor eletroquímico. Em vista disso, o presente trabalho descreve a modificação química do óxido de grafeno com o dendrímero PAMAM G.0 (OGP) e posterior reação com hexacianoferrato (II) e (III) de potássio e nitrato de cério (III) para aplicação eletroanalítica. Os materiais híbridos formados (OGPH(II)Ce e OGPH(III)Ce) foram caracterizados por diferentes técnicas, tais como: Espectroscopia de Fotoelétrons Excitados por Raios-X (XPS), Espectroscopia na Região do Infravermelho com Transformada de Fourier (FTIR), Espectroscopia de Energia Dispersiva de Raios-X (EDX), Microscopia Eletrônica de varredura (MEV) e Difração de Raios-X (DRX). Como aplicação eletroanalítica, os mesmos foram empregados com sucesso na eletro-oxidação catalítica de Ácido Ascórbico e Dopamina, utilizando para tal finalidade o eletrodo de pasta de grafite e a técnica de voltametria cíclica. O eletrodo de pasta de grafite modificado com OGPH(... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: Graphene oxide (GO) belongs to a new class of two-dimensional crystalline materials that has excelled in the inter and multidisciplinar scientific field due to special properties that enables its apllication in nanomembranes, supercapacitors, biosensors, drug releaser; among others. Its strutcture consists on an individual layer of ornate graphene with oxygenated functional groups that allow the graphene oxide to be chemically modified with several molecules, atoms or metallic ions, which can result in an excellent electrochemical sensor. Therefore, the present work describes the chemical modification of the graphene oxide with the PAMAM G.0 (GOP) dendrimer and subsequent reaction with potassium hexacyanoferrate (II) and (III) and cerium nitrate (III) for electroanalytical application. The hybrid materials formed (GOPH(II)Ce and GOPH(III)Ce) were characterized by different techniques, such as: X Rays Photoelectron Spectroscopy (XPS), Fourier Transform Infrared Spectroscopy (FTIR), Scanning Electron Microscopy (SEM), Energy Dispersive X- rays Spectroscopy (EDS) and X-ray diffraction (XRD). As an electroanalytical application, the same were successfully used in the catalytic electro-oxidation of Ascorbic Acid and Dopamine, using for this purpose the graphite paste electrode and the cyclic voltammetry technique. The graphite paste electrode modified with GOPH(II)Ce presented two linear regions for the catalytic electro-oxidation of Ascorbic Acid, wherein the first region present... (Complete abstract click electronic access below) / Mestre

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Zwei Modellreaktionen wurden mit thermoresponsiven Nanoreaktoren untersucht. Die Reduktion von 4-Nitrophenol und von Kaliumhexacyanidoferrat(III) mit Natriumborhydrid. Die Nanoreaktoren bestehen aus einem Polystyrol Kern, umgeben von einer Hydrogel Schale aus Poly-(N-Isopropylacrylamid). Die Reaktionen werden auf der Oberfläche von Metall Nanopartikeln in der Hydrogel Schale katalysiert. In einer auf Gold- und Silberkatalysatoren fokussierten Literaturstudie zeigte sich, dass der geschwindigkeitsbestimmende Reaktionsschritt zwischen beiden Metallen variieren könnte. Kinetische Studien mit Silber haben gezeigt, dass ein erfolgreich auf Gold angewandtes Modell modifiziert werden muss um auf Silber anwendbar zu sein und haben gezeigt, dass sich die Kinetik der Reaktion auf beiden Metallen unterscheidet. Die weitere Analyse ergab die typische, nicht der Arrhenius Abhängigkeit folgende, Abhängigkeit der Reaktionsrate von der Temperatur und hat gezeigt, dass die Partitionierung der Reaktanden im Hydrogel für das kinetische Modell relevant ist. Die Reduktion von Kaliumhexacyanidoferrat(III) auf Gold hat gezeigt, dass elektrostatische Effekte hier eine maßgebliche Rolle spielen. Ein kinetisches Modell wurde erarbeitet, dass die relevanten Einflussfaktoren durch Hydrogel, Geometrie der Nanoreaktoren, diffusions- und elektrostatische Effekte miteinbezieht. Die gewonnenen Daten konnten mittels eines auf der Auswertung des stationären Zustands basierenden Modells erfolgreich gefittet werden. Hierbei wurde das komplexe Zusammenspiel von elektrostatischen Effekten, deren Abschirmung und Einfluss auf die Diffusion sowie die Reaktionsrate gezeigt. Mit wenigen physikalisch aussagekräftigen Fitparametern konnten alle beobachteten Effekte erfolgreich erklärt werden. Der Vergleich der Reduktion von 4-Nitrophenol und von Hexacyanidoferrat(III) zeigt hierbei die entscheidenden Faktoren sowohl für reaktions- als auch für diffusionskontrollierte Reaktionen in thermoresponsiven Hydrogelen. / Two model reactions were investigated with thermoresponsive core-shell nanoreactors, the reduction of 4-nitrophenol and of potassium hexacyanoferrate(III), both reduced with sodium borohydride. The nanoreactors comprise of a polystyrene core surrounded by a hydrogel shell of poly-N-isopropylacrylamide (PNIPAM) crosslinked with N,N’-methylenebisacrylamide. Metal nanoparticles are immobilized inside the hydrogel shell on the surface of which the model reactions are catalyzed. In the reduction of 4-nitrophenol, special emphasis is laid on the reduction on gold and silver catalysts. A literature review of mechanistic as well as kinetic studies reveals that the rate determining step may differ between the two catalyst metals. Kinetic investigations with a silver catalyst reveal that the kinetic model derived previously for gold catalysts needs to be modified for the kinetic analysis in this study, confirming a difference in the kinetics for both catalyst metals. The temperature dependent analysis reveals the typical non-Arrhenius dependency of the reaction rate and shows that the partition ratio of the reactants is relevant for the kinetics. The reduction of potassium hexacyanoferrate(III) on gold reveals that electrostatic effects play a major role in this reaction. A new kinetic model is derived, accounting the relevant influence factors of the hydrogel, the nanoreactor geometry, diffusional and electrostatic effects. With a stationary state approach the experimental data are fitted successfully, revealing the complex interplay of electrostatic effects, the screening thereof and the influence on diffusion and reaction rate. With only a few physically meaningful fit parameters all observed effects can be explained successfully. The comparison of the reduction of 4-nitrophenol and potassium hexacyanoferrate(III) highlights the decisive factors in both, reaction and diffusion controlled reactions inside thermoresponsive hydrogels.