Double-resonance and two-dimensional silicon-29 NMR spectroscopy of minerals

Results of novel double-resonance and two-dimensional ²⁹Si NMR measurements, including ²⁷Al-to-²⁹Si and ²³Na-to-²⁹Si cross-polarization, ²⁹Si isotropic/anisotropic correlation, and ¹H/²⁹Si heteronuclear correlation experiments are reported. ²⁷Al-to-²⁹Si and ²³Na-to-²⁹Si cross-polarization were used to improve sensitivity, making two-dimensional ²⁹Si NMR techniques more feasible. ²⁹Si two-dimensional isotropic/anisotropic correlation spectra of the minerals albite, sepiolite, and gyrolite were measured and the principal components of the chemical-shift tensor for each site determined. A modified version of the TOSS-reTOSS pulse sequence was used and is shown to yield pure-phase isotropic/anisotropic correlation spectra. ¹H/²⁹Si heteronuclear correlation spectra of gyrolite and sepiolite were measured and used to assign ²⁹Si resonances to distinct crystallographic sites, to determine the proximity between silicon and hydrogen atoms, and to study ¹H-to-²⁹Si cross-polarization dynamics.