Magnetic susceptibility effects on C-13 MAS NMR spectra of carbon materials and graphite

C-13 high-resolution solid-state nuclear magnetic resonance (NMR) was emplo yed to study carbon materials prepared through the thermal decomposition of four different organic precursors (rice hulls, endocarp of babassu coconut , peat, and PVC). For heat treatment temperatures (HTTs) above about 600 de greesC, all materials presented C-13 NMR spectra composed of a unique reson ance line associated with carbon atoms in aromatic planes. With increasing HTT, a continuous broadening of this resonance and a diamagnetic shift in i ts central frequency were verified for all samples. The evolution of the ma gnitude and anisotropy of the magnetic susceptibility of the heat-treated c arbon samples with HTT explains well these findings. It is shown that these results are better understood when a comparison is made with the features of the C-13 NMR spectrum of polycrystalline graphite, for which the magneti c susceptibility effect is also present and is much more pronounced. (C) 20 01 Academic Press.