Use of solid state NMR in a multinuclear approach to the study of porous carbonaceous materials.

Name: Thiérry Ramos Lopes
Type: PhD thesis
Publication date: 06/09/2017

Namesort descending Role
Jair Carlos Checon de Freitas Advisor *

Examining board:

Namesort descending Role
Jair Carlos Checon de Freitas Advisor *
Jorge Luis Gonzalez Alfonso Internal Examiner *
Leonardo Cabral Gontijo External Examiner *
Thiago Eduardo Pedreira Bueno External Examiner *
Tito José Bonagamba External Examiner *
Wanderlã Luis Scopel Internal Examiner *

Summary: 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 acti-vation (using H3PO4 - named as EBP samples). The activated carbons exhibited high specific 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 identification of a significant 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 different 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 H3PO4 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 different 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.

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