High-resolution solid-state NMR study of the occurrence and thermal transformations of silicon-containing species in biomass materials

The occurrence of silicon in two kinds of biomass (rice hulls and endocarp of babassu coconut) and the thermal transformations taking place in these m aterials under heat treatments are studied here. We report also the product ion, characterization, and study of carbonaceous materials with high SiC co ntent through the carbothermal reduction of silica, using these natural pre cursors. X-ray diffraction, scanning electron microscopy, and C-13 and Si-2 9 room temperature high-resolution solid-state NMR measurements are used in the characterization and study of the materials as well as the process of SiC formation. Important conclusions about the nature of silicon in these t ypes of biomass and the effects of heat treatments on the structure of sili con-containing species are derived from the results presented. It is shown that silicon in these materials occurs in two distinct forms: amorphous hyd rated silica and organically bound silicon species. The influence of spin-l attice relaxation dynamics on the NMR spectra is discussed, evidencing the role played by the paramagnetic defects produced in the materials through p yrolysis.