Investigation of carbonaceous and lignocellulosic materials by solid state 13C nuclear magnetic resonance.

Name: Daniel Fernandes Cipriano
Type: PhD thesis
Publication date: 03/12/2019

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 *
Paulo Roberto Filgueiras External Examiner *
Tito José Bonagamba External Examiner *
Wanderson Romão External Examiner *

Summary: Solid-state 13C nuclear magnetic resonance (NMR) spectroscopy was used in investigations of different biomass materials from Brazil, as well as in studies of the structural properties of carbon materials such as chars derived from phenolic resin, graphite oxide and reduced graphite oxide. In the case of the biomass materials, methods for determining the lignin, cellulose and hemicellulose contents of different lignocellulosic feedstocks were evaluated, using 13C NMR with cross polarization (CP) and magic angle spinning (MAS). The lignin contents were evaluated by means of the calibration of the intensity of the signal due to methoxyl groups present in the 13C CP/MAS NMR spectra of 41 different samples of lignocellulosic materials. A method for the determination of the lignin, cellulose and hemicellulose contents was also developed, using the technique of multivariate curve resolution with alternating least squares to analyze the 13C CP/MAS NMR spectra of 11 lignocellulosic biomass samples and 18 mixtures of cellulose, lignin and xylose. The results obtained with the use of these two methodologies were in reasonable agreement with the experimental results obtained by chemical quantification methods. Regarding the studies of carbon materials, the single pulse (SP) and CP methods were used in MAS experiments, WHEREas the spin-echo method was employed in experiments with static samples, in order to evaluate the effect of heat treatments on the structure of chars produced from a phenolic resin precursor. From the 13C CP/MAS and SP/MAS NMR spectra, it was possible to follow the evolution of the chemical structure of the chars as a function of the heat treatment temperature and to study the processes of spin-lattice relaxation in these systems. By means of spin-echo experiments performed with static samples, it was possible to analyze the 13C NMR powder patterns of the heat-treated chars and to observe the growth of the chemical shift anisotropy with the increase in the heat treatment temperature. Similar studies were also conducted with graphite, milled graphite, graphite oxide and reduced graphite oxide samples. The profile of the 13C NMR powder patterns observed for these materials was influenced by the diamagnetic susceptibility and the partial alignment of the particles with respect to the static magnetic field.

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