Estudo de reatividade de materiais orgânicos: síntese de melanina e sensores químicos baseados em nanoflakes de carbono.
Data
2020-04-06
Autores
Alves, Gabriel Gomes Baltazar
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Editor
Universidade Estadual Paulista (Unesp)
Resumo
Compostos baseados em carbono têm se mostrado materiais de grande interesse tecnológico, principalmente devido à sua alta flexibilidade de síntese, baixo custo relativo e propriedades únicas. Graças a isto, tem-se observado um número crescente de trabalhos teóricos e experimentais acerca da compreensão de características básicas destes sistemas e a proposição de novos compostos com propriedades otimizadas para aplicações específicas. No presente trabalho são apresentados estudos teóricos acerca de dois temas relacionados à reatividade e propriedades estruturais de materiais orgânicos e baseados em carbono: i) estudo e análise de reatividade de subunidades de melanina; e ii) estudo estrutural e de reatividade de nanoflocos (ou nanoflakes em inglês) de carbono para aplicações em sensores químicos. Melaninas são pigmentos naturais com propriedades biológicas e eletrônicas que as tornam promissoras para aplicações bio-eletrônicas. Contudo não há ainda entendimento pleno acerca de sua estrutura macromolecular e conexão entre suas unidades básicas. Neste estudo cálculos de estrutura eletrônica, combinados com análise de reatividade, foram realizados para melhor compreender os processos de oligomerização. Os resultados obtidos permitem propor as estruturas diméricas mais prováveis e identificar reações que ocorrem no processo de síntese de melanina. Pode-se também estabelecer uma ordem de dominância de reatividade entre as subunidades e identificar núcleos de polimerização, o que pode auxiliar na definição de novas rotas sintéticas e modificações químicas destes biomateriais. O segundo tema traz estudos sobre diferentes geometrias e derivados de nanoflakes de carbono, bem como sua possível aplicação como sensor químico. Neste estudo foram avaliadas cinco diferentes geometrias e 11 modificações químicas destes materiais, cuja reatividade e estrutura eletrônica foram avaliadas. Os resultados obtidos sugerem uma grande variação de reatividade em todas as propriedades dos nanoflakes devido a sua geometria e terminações. Em geral, bordas do tipo zigzag são mais reativas. A análise comparativa dos níveis de fronteira dos derivados com diferentes analitos gasosos sugere a potencialidade das geometrias contendo bordas armchair como possíveis detectores dos gases Cl2 e SO2. De maneira geral, os resultados advindos de ambos os temas evidenciam a potencialidade do uso de índices de reatividade na análise de propriedades básicas e aplicadas de materiais orgânicos e estruturas de carbono.
Carbon-based materials have been considered compounds of great technological interest, manly due to their flexibility of synthesis, relative low cost and unique opto-electronic properties. A crescent number of theoretical and experimental studies has been reported regarding the comprehension of basic features of these materials and the proposition of new compounds with optimized properties. This thesis presents studies about the reactivity and structural properties of carbon based and organic materials according to two themes: i) reactivity study and oligomerization analysis of melanin; and ii) reactivity and structural analysis of carbon nanoflakes and their application as chemical sensors. Melanins are natural pigments with biological and electrical properties that turn them promising compounds for bioelectronic applications. However, despite of their promising properties, up to date the macromolecular structure of melanin and the connection between its basic units have not been understood in detail. In this study, electronic structure calculations, combined with reactivity analysis were conducted to better understand the oligomerization process of this compound. The obtained results allow us to propose the most probable dimeric structures and identify relevant reactions that occur during melanin oligomerization process. Furthermore, it was possible to observe a dominance order in the reactivity of the subunits and identify possible nucleation centers of melanin polymerization, which are valuable informations for the design of new synthetic routes and chemical modifications. In the second theme it was investigated the influence of geometries and chemical modifications in the reactivity and electrical properties of carbon nanoflakes, aiming their application in chemical sensors. Five different geometries and 11 chemical modifications of these materials were evaluated in the framework of the density functional theory. The obtained results indicate the existence of significant changes in the compounds reactivities due to their geometries and terminations. In general, zigzag edges are more reactive than armchair ones. A comparative analysis between the frontier levels of derivatives and gaseous analytes suggest a potential application of armchair edged systems as detectors of Cl2 and SO2. In general, the results from both themes show the potential of evaluating reactivity indices to better understand some basic and applied properties of organic materials and carbon-based structures.
Carbon-based materials have been considered compounds of great technological interest, manly due to their flexibility of synthesis, relative low cost and unique opto-electronic properties. A crescent number of theoretical and experimental studies has been reported regarding the comprehension of basic features of these materials and the proposition of new compounds with optimized properties. This thesis presents studies about the reactivity and structural properties of carbon based and organic materials according to two themes: i) reactivity study and oligomerization analysis of melanin; and ii) reactivity and structural analysis of carbon nanoflakes and their application as chemical sensors. Melanins are natural pigments with biological and electrical properties that turn them promising compounds for bioelectronic applications. However, despite of their promising properties, up to date the macromolecular structure of melanin and the connection between its basic units have not been understood in detail. In this study, electronic structure calculations, combined with reactivity analysis were conducted to better understand the oligomerization process of this compound. The obtained results allow us to propose the most probable dimeric structures and identify relevant reactions that occur during melanin oligomerization process. Furthermore, it was possible to observe a dominance order in the reactivity of the subunits and identify possible nucleation centers of melanin polymerization, which are valuable informations for the design of new synthetic routes and chemical modifications. In the second theme it was investigated the influence of geometries and chemical modifications in the reactivity and electrical properties of carbon nanoflakes, aiming their application in chemical sensors. Five different geometries and 11 chemical modifications of these materials were evaluated in the framework of the density functional theory. The obtained results indicate the existence of significant changes in the compounds reactivities due to their geometries and terminations. In general, zigzag edges are more reactive than armchair ones. A comparative analysis between the frontier levels of derivatives and gaseous analytes suggest a potential application of armchair edged systems as detectors of Cl2 and SO2. In general, the results from both themes show the potential of evaluating reactivity indices to better understand some basic and applied properties of organic materials and carbon-based structures.
Descrição
Palavras-chave
Cálculo de estrutura eletrônica, Índices de reatividade, Materiais orgânicos, Melaninas, Nanoflakes, Polimerização, Compostos baseados em carbono, Electronic structure calculation, Reactivity indexes, Nanoflakes, Organic materials, Melanins, Polymerization