In this work, the modification of conducting substrates with thin (nanometer thick) aryl films via reaction with aryldiazonium salts was investigated. Two methods were used: modification by electro-reduction of the aryldiazonium salts and modification by spontaneous reaction of aryldiazonium the salts with the surface at open circuit potential. The majority of the studies were undertaken using p-nitrobenenze diazonium salt, which gives electro-active nitrophenyl (NP) films at the surface that can be detected and characterized by cyclic voltammetry. Films prepared spontaneously on carbon and gold electrodes at open circuit potential were characterized by electrochemistry, atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS) and water contact angle measurements. At both carbon and gold, spontaneous modification proceeds via electron transfer from the surface to the diazonium salt.Furthermore, on both types of surface, spontaneously prepared NP films were found to be loosely packed multilayers of less than 5 nm in thickness. The spontaneous reaction was utilized for the patterning of carbon, gold, silicon and copper surfaces by microcontact printing (μCP) with diazonium salts. The presence of spontaneously formed films upon printing was confirmed by cyclic voltammetry and AFM. The films were demonstrated to be useful for the tethering of further molecules to the surface. Patterns prepared by μCP were imaged using scanning electron microscopy (SEM) and condensation figures. The preparation of two-component systems, with different chemical functionalities attached to different, well-defined, regions of the surface, was demonstrated. The optimization of the long term activity of glucose oxidase hydrogels by covalent attachment of the hydrogels to modified carbon electrodes was investigated. Covalent attachment was demonstrated, but the resulting electrode-hydrogel surfaces did not show long-term activities superior to those for physisorbed hydrogels. It is suggested that the limiting factor for long-term hydrogel activity is not adhesion of the hydrogel to the surface, but degradation of enzymatic activity by H2O2.

Orientador: Carlos Roque Duarte Correia / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Quimica / Made available in DSpace on 2018-08-06T00:38:56Z (GMT). No. of bitstreams: 1 Pastre_JulioCezar_M.pdf: 2844371 bytes, checksum: 6abfb0e87d60113816e3b01d9a02d6b9 (MD5) Previous issue date: 2005 / Mestrado / Quimica Organica / Mestre em Química

Ce travail de thèse concerne la préparation et caractérisation des électrodes de carbone vitreuses (GC) modifiées par les films de groupements aryl (substitués) ou par phtalocyanines des métaux (MPc) et l'évaluation de leurs activités catalytiques envers la réduction électrochimique des nitrates dans les milieux aqueux acides. Les techniques adoptées pour la modification de surface du substrat (le GC) consistent à la réduction électrochimique des sels de diazonium ou à l'abrasion physique de la surface contre la poudre des MPc. En faisant intervenir un mécanisme complexe, y compris les phénomènes d'adsorption du réactif et du produit sur la surface, l’électroréduction de sels de diazonium entraîne au greffage des groupements aryls sur la surface. Les analyses voltamétriques détaillées ont rendu possible de conclure, décisivement pour la première fois, que la réduction commence à se faire sur la surface entière et, selon la concentration du diazonium et/ou l'efficacité du greffage, peut continuer à se faire à traverse les ouvertures microscopiques générés parmi les groupements aryl greffés sur la surface durant l'étape précédente de réduction (...) / This thesis work concerns about the preparation, characterization and catalytic activities evaluation of (substituted) aryl and metallophthalocyanines films-modified glassy carbon (GC) electrodes towards nitrate electrochemical reduction in acidic aqueous media. The surface modification techniques adopted consisted of the electroreduction of 4-substituted aryl diazonium salts and the metallophthalocyanine (MPc) powder abrasive adsorption. Through a complex mechanism involving the reactants and products adsorptions on the substrate surface, the electroreduction of aryl diazonium salts leads to the covalent attachment of mono as well as multilayers of aryl groups on the substrate surface. Detailed voltammetric investigations enabled to conclude, decisively for the first time, that the diazonium cation reduction begins to take place on the bulk (whole) surface and, depending upon the concentration and/or the products grafting efficiency, may continue to take place across the microscopic pinholes formed among the aryl groups grafted on the surface during the previous reduction step, thereby explaining the origin of the two reduction peaks in the voltammograms on GC surface. Electrochemical characterization of 4-nitrophenyl(NP)-modified surfaces in various types of aqueous media shed light over a number of mechanistic aspects of the process. Some new electrochemical evidences of the complications of surface coverage determination of redox centers from their electrochemical responses and of the role of aqueous electrolyte species transport on the responses have been presented. Some new phenomena or observations such as identification of the regions of votammograms corresponding to aminophenyl and hydroxyaminophenyl formation of the surface bound NP groups reduction, identification of the method of surface bound NP groups surface coverage estimation from the total width at half wave maximum (or electron transfer coefficient) of the responses, identification of the mechanistic aspects governing the differences of voltammetric behaviors of surface bound NP layers and the solution phase nitrobenzene, electrochemical (and XPS) evidences of the presence of azo type functionalities in the aryl films prepared from aryldiazonium electroreduction were also noticed. Barrier characters of the aryldiazonium electroreduction-derived N,N-dimethylaminophenyl-, nitrophenyl- and aminophenyl-modified surfaces towards ferricyanide, hexaammineruthenium and proton electroreductions in aqueous media indicate to the existence of electrostatic interactions among the surface bound and the solution phase ionic species. However, upon negative potential applications (such as those of water or nitrate reductions) surface attached films are partly or completely lost from the surface, as evidenced by the analytical scale measurements as well as from potentiostatic electrolysis of nitrate reduction in acidic aqueous media. Concerning the MPc-modified GC surfaces, the analytical scale measurements showed that among the phthalocyanines of copper, Iron and Nickel, the one of Cu is an optimizing material for the nitrate electrochemical reduction in, not previously reported, acidic aqueous media. The catalytic activity of MPc powders towards nitrate reduction in these media, which varies in the order CuPc > FePc > NiPc > GC appears to be related to the mental center and not with the phthalocyanine ring