Metalopolimeros são considerados excelentes materiais para a construção de eletrodos modificados quimicamente devido ao fato de apresentar propriedades essenciais, como por exemplo, uma alta atividade eletrocatalítica, eletroluminescia, aplicações na área da eletroquímica e eletroanalítica em atividades de eletrocatálise, quimioresistores, fotoeltrocatálise e desenvolvimento de sensores, respectivamente. Alguns complexos de metais de transição contendo Bases de Schiff como ligantes exibem propriedades eletrônicas não convencionais, que têm sido extensivamente estudadas para a aplicação no desenvolvimento de modelos sintéticos aos compostos biológicos como as metaloproteínas e metaloenzimas. O intuito principal desta tese foi o estudo da síntese, otimização e aplicação do nano-metalopolimero à base de poli[Ni(Salpn)] como plataforma sensorial eletroquímica, visando a obtenção de melhoras significativas em determinadas propriedades estruturais, catalíticas, dentre outras. Essas propriedades dependem, não somente do comportamento molecular, mas também, dos efeitos dos possíveis rearranjos estruturais devido às interações intermoleculares. Desta forma, foi construído e estudado o desempenho eletroquímico de uma plataforma sensorial à base de eletrodos constituídos com filmes poliméricos, sendo possível a avaliação de suas aplicações na determinação de substâncias com importância analítica nas áreas clínica, farmacêutica e ambiental. No âmbito que tange a síntese e caracterização do complexo Ni(Salpn), foi possível confirmar por meio de técnicas de caracterização de materiais a eficiência do métodos utilizados. Analogamente, a eletropolimerização foi realizada com sucesso, obtendo nano-filmes com espessura aproximada 110 nm com ótima atividade eletroquímica. A avaliação na aplicação do nano-metalopolímero poli[Ni(Salpn)] apresentou uma excelente resposta frente ao H2O2, possuindo uma rápida resposta, um intervalo linear de 49,9 a 1480 μmol L-1, com limite de detecção de 7,68 μmol L-1 e sensibilidade de 24,05 μÅ mmol-1, viabilizando assim a construção de uma plataforma sensorial viável, rápida, precisa e exata, com a finalidade de resolução de problemas analíticos. / Metalopolymers are considered to be excellent materials for the construction of chemically modified electrodes due to the fact that they present essential properties, such as high electrocatalytic activity, electroluminescence, electrochemical and electroanalytical applications in electrocatalysis, chemoresistors, photoeltrocatalysis and sensor development, respectively. Some transition metal complexes containing Schiff Bases as binders exhibit unconventional electronic properties which have been extensively studied for application in the development of synthetic models for biological compounds such as metalloproteins and metalloenzymes. The most aim of this thesis was to study the synthesis, optimization and application of nano-metallopolymer based on poly [Ni(Salpn)] as an electochemical sensorial platform, aiming at obtaining significant improvements in certain structural, catalytic properties, among others. These properties depend not only on molecular behavior but also on the effects of possible structural rearrangements due to intermolecular interactions. In this way, the electrochemical performance of a sensorial platform based on electrodes made with polymer films was constructed and studied, being possible the evaluation of its applications in the determination of substances with analytical importance in the clinical, pharmaceutical and environmental areas. In terms of the synthesis and characterization of the Ni(Salpn) complex, it was possible to confirm by means of techniques of material characterization the efficiency of the methods used. Analogously, the electropolymerization was performed successfully, obtaining nano-films with a thickness of approximately 110 nm with excellent electrochemical activity. The evaluation in the application of the poly[Ni(Salpn)] nano-metallopolymer showed an excellent response against H2O2, having a fast response, a linear range of 4.99 x 10-5 to 1.48 x 10-3 mol L-1, with detection limit of 7.68 x 10-6 mol L-1 and sensitivity of 24,05 μmol mmol-1, thus making possible the construction of a viable, fast, precise and accurate sensorial platform for the purpose of resolution of analytical problems.

No description available.

Rapid industrial globalization and technological development and energy consumption across the globe has significantly increased in response to mounting energy needs. The necessity for alternative and sustainable energy conversion devices has become apparent with the growth of energy utilization. In recent years, many research efforts have been made in the development of low-cost, efficient, environmentally friendly energy conversion devices. One type of energy conversion device, polymer electrolyte membrane fuel cells (PEMFCs), uses hydrogen oxidation at the anode and oxygen reduction at the cathode, with a solid-state proton conducting membrane between to generate energy with water as a by-product. PEMFCs use Nafion®, a sulfonated fluoropolymer-copolymer for proton transport; however, temperature restraints and the need for hydration limits the efficacy of this polymer. Moreover, the kinetics of oxygen reduction (ORR) are significantly slower at the cathode than the anode. Platinum is currently the industry standard, but these materials have limited resources, are expensive, and can be sensitive to carbon monoxide poisoning. Platinum is also the preferred catalyst for hydrogen evolution reactions (HER)—critical electrochemical reactions at the cathode for water splitting applications for the generation of hydrogen. Metal-Organic Frameworks (MOFs) have been explored for proton conductivity and as electrode catalysts. The tunability of metal ions and organic linkers both in situ and post-synthesis allows for the targeted design of specific surface areas and topologies while fine tuning selective functionality. Furthermore, due to morphology retention upon pyrolysis, MOFs are good platforms for logical design both pre- and post- carbonization. Taking advantage of the amendable design, along with tunable porosity and growth in controlled dimensions, this work explores the modification of a zinc based MOF as a possible candidate for proton conduction, as well modification of zinc, cobalt, and iron based MOFs for ORR catalysis. Post-synthetic modification was employed as a technique to oxidize the imidazolate ligand to include carboxylic acid functionality of a zinc based MOF. Proton conductivity generally arises from the mobility of the charge carriers present (i.e. carboxylates and phosphates). The incorporation of Brønsted acidity by way of free carboxylates is often challenging, as these are generally sites of coordination in the framework. Herein, we report the successful augmentation of Brønsted acidity with retention of framework crystallinity in a robust MOF. Additionally, the effects of metal content and carbonization temperature of MOFs were explored for ORR and HER. Cobalt and iron were doped either pre- or post-synthesis and carbonized in an inert atmosphere at various temperatures to generate MOF-derived carbons with catalytically active centers without the need for additional support. Carbons with parent MOFs containing moderate amounts of cobalt doping in a bimetallic Co/Zn MOF, or carbons that contained no zinc in the parent material, showed excellent electrocatalytic performance for ORR when carbonized at temperatures just at or above the boiling point of zinc. Zinc based MOFs were doped with various amounts of iron post-synthesis and prior to carbonization in an inert atmosphere. The formation of iron nanoflakes and nanorods on the surface of these carbons generated from the pyrolysis of these iron doped MOFs yielded high surface areas and outstanding electrochemical performance for ORR in both acidic and alkaline media. Likewise, excellent HER catalysis was exhibited by the MOF-derived carbon matrix with the highest iron loading pre-carbonization and more disperse nanorods. Not only does the amenability of MOFs make them a good platform for the direct inclusion of essential electrochemically active moieties, but it also allows for more targeted, nuanced, and rational design of materials needed to enhance proton conduction and electrochemical performance, particularly in cases on non-precious metal electrocatalysts where mechanisms are often not well-understood.

Thesis (Ph.D.)--University of Delaware, 2006. / Principal faculty advisor: Jingguang G. Chen, Dept. of Chemical Engineering. Includes bibliographical references.

Controlling catalyst morphology and composition are required to make meaningful structure-activity/stability relationships for the design of future catalysts. Herein, we have employed strategies of presynthesis and infusion or electroless deposition to achieve exquisite control over catalyst composite morphology. The oxygen reduction (ORR) and the oxygen evolution reactions (OER) were chosen as model systems, as their slow kinetics is a major limiting factor preventing the commercialization of fuel cells and rechargeable metal air batteries. In acid, bimetallic (Pt-Cu, Pd-Pt) and monometallic (Pt) catalysts were presynthesized in the presence of capping ligands. Well alloyed Pt-Cu nanoparticles (3-5 nm) adsorbed on graphitic mesoporous carbon (GMC) displayed an ORR activity >4x that of commercial Pt. For both presynthesized Pt and Pt-Cu nanocrystals on GMC, no activity loss was also observed during degradation cycling due to strong metal-support interactions and the oxidation resistance of graphitic carbon. Similar strong metal-support interactions were achieved on non-graphitic carbon for Pd3Pt2 (<4 nm) nanoparticles due to disorder in the metal surface This led to enhanced mass activity 1.8x versus pure Pt, as well as improved stability. For basic electrolytes, we developed an electroless co-deposition scheme to deposit Ag (3 nm) next to MnOx nanodomains on carbon. We achieved a mass activity for Ag-MnOx/VC, 3x beyond the linear combination of pure component activities due to ensemble effects, where Ag and MnOx domains catalyze different ORR steps, and ligand effects from the unique electronic interaction at the Ag-MnOx interface. Activity synergy was also shown for Ag-Pd alloys (~5 nm), achieving up to 5x activity on a Pd basis, resulting from the unique alloy surface of single Pd atoms surrounded by Ag. Lastly, we combined arrested growth of amorphous nanoparticles with thin film freezing to create a high surface area, pure phase perovskite aggregate of nanoparticles after calcination. Sintering was mitigated during the high temperature calcination required to form the perovskite crystals. The high surface areas and phase purity led to OER mass activities ~2.5x higher than the benchmark IrO2 catalyst. / text

This dissertation explores the use of nanocarbons both as conductive supports for redox enzyme electrochemistry and as electrocatalytic components for the nonmediated detection of biogenic analytes. More specifically, the influence of nitrogen doping of these nanocarbons (referred to herein as nitrogen-doped carbon nanotubes, or N-CNTs) on their bioelectrocatalytic performance is studied through direct enzyme adsorption and exploitation of the N-CNTs' inherent reactivity toward H₂O₂ to create H₂O₂-based sensing strategies. Both nondoped CNTs and N-CNTs may be effectively incorporated into biogenic sensing assemblies, as demonstrated herein using a variety of electrochemical techniques. Chapter 1 gives a general overview of the scope of this research and describes previous studies conducted within our laboratories that demonstrate our CNTs' promise as biogenic electrode materials. Chapter 2 describes the chemical vapor deposition (CVD) method used to prepare both CNTs and N-CNTs and establishes their suitability for use in the detection schemes outlined in later chapters through long-term stability studies. Additionally, the redox activity of Fe nanoparticles entrapped in the CNTs as a result of this CVD growth process is examined using a host of electrochemical experiments. Importantly, the data presented in this chapter show that these Fe particles do not explain the observed electrocatalytic response of the CNTs. Chapter 3 explores the direct adsorption of horseradish peroxidase (HRP) at both nondoped and N-CNTs. Spectroscopic and electrochemical assays are used to compare the extent of HRP enzymatic activity upon immobilization at both types of CNTs. Both types of HRP/CNT composites are then utilized in a quantitative H₂O₂ sensing strategy. Chapter 4 discusses the intrinsic reactivity of N-CNTs toward H₂O₂. Koutecky-Levich plots are used to demonstrate differences in H₂O₂ consumption mechanisms between NCNTs and traditional peroxidases. By replacing HRP with N-CNTs in an amperometric glucose detection scheme, the versatility of N-CNTs as a peroxidase substitute for biogenic analyte detection is demonstrated. Chapter 5 outlines future directions for this research, including possible strategies for improving electron transfer between HRP and both types of CNTs. This chapter also presents a newly developed, mediated oxidase-substrate electrochemical detection method that can easily be modified to incorporate CNTs.

No description available.

Thesis (Ph. D.)--University of Texas at Austin, 2007. / Vita. Includes bibliographical references.

Thesis (M.S.)--University of Delaware, 2007. / Principal faculty advisors: Jingguang G. Chen, Dept. of Chemical Engineering; and Thomas P. Beebe, Jr., Dept. of Chemistry & Biochemistry. Includes bibliographical references.

Thesis (Ph. D.)--University of Washington, 1999. / Vita. Includes bibliographical references (leaves 121-125).