Utilização de RMN no estado sólido em uma abordagem multinuclear para estudo de materiais carbonosos porosos.

• Ano de defesa: 2017
• Autor(a) principal: Lopes, Thierry Ramos
• Tipo de documento: Tese
• Tipo de acesso: Acesso aberto
• Idioma: por
• Instituição de defesa: Universidade Federal do Espírito Santo; BR; Doutorado em Física; Centro de Ciências Exatas; UFES; Programa de Pós-Graduação em Física
• Palavras-chave em Português: Activated carbon; Porous materials; Endocarp of babassu coconut; solid-state NMR; Carvão ativado; Materiais porosos; Endocarpo de babaçu; RMN no estado sólido; Física; 53
• Link de acesso: http://repositorio.ufes.br/handle/10/7383

This work is concerned with a study of activated carbons prepared by physical and chemical activation, using solid-state nuclear magnetic resonance (NMR) spectroscopy in a multinuclear approach. The activated carbons were obtained starting from the endocarp of babassu coconut (EB), either by physical activation (with steam named as EBF samples) or by chemical activation (using H3P O4 named as EBP samples). The activated carbons exhibited high speci c surface area, with values depending on the experimental conditions used in each synthesis. The 1H NMR spectra of the EBF samples showed two major peaks with chemical shifts changing as a function of the activation temperature. The broader peak was associated with 1H nuclei in aromatic groups, the other being associated with adsorbed water. In order to better understand these results, hydrated samples of milled graphites were also studied by 1H NMR, allowing the identi cation of a signi cant variation of the chemical shift of the peak due to adsorbed water as a function of the increase in the milling time (which caused structural changes in the milled graphites). The chemical nature of the phosphorus-containing species in the EBP samples was studied by 1H, 13C and 31P solid-state NMR spectroscopy, including 2D 1H -31 P correlation experiments, which allowed the detection of the formation of di erent phosphorus compounds (mostly containing phosphate groups) embedded into the porous carbon network. Due to the natural occurrence of silicon compounds in the endocarp of babassu coconut, the chemical activation with H3P O4 was found to produce silicon pyrophosphate nanocrystals. Nanocomposites containing nanostructured Al compounds were obtained by impregnation of EBF and EBP samples with Al(NO3)9H2O, followed by heat treatments at di erent temperatures; 27Al NMR spectra were used to analyze the coordination type of the Al3+ cations present in each sample, which was changed depending on the heat treatment temperature.