We have measured 29Si, 27Al, and 1H NMR spectra of kaolinites with natural and synthetic origins, using high-resolution solid-state techniques such as the magic angle spinning and the multipulse sequences. The 29Si spectra demonstrate clearly that two inequivalent Si sites are present, and the origin of the line width has been discussed quantitatively. The line shape of the 27Al spectra is governed by the second-order quadrupole interaction and suggests the presence of two inequivalent Al sites with different quadrupole coupling constants and asymmetry factors. The 1H static spectra are broadened by the dipole-dipole interactions between 1H spins and between 1H and 27Al spins, indicating that the hydrogen atoms in the hydroxyl groups are in a rigid lattice state at room temperature. The technique of combined rotation and multiple-pulse spectroscopy has been successfully applied to kaolinites. The 1H chemical shift of the hydroxyl groups is 2.8 ppm from tetramethylsilane.
All Science Journal Classification (ASJC) codes
- Physical and Theoretical Chemistry