Characterization of Nanostructured Organic-Inorganic Hybrid Materials Using Advanced Solid-State NMR Spectroscopy

We demonstrate the applications of several novel techniques in solid-state nuclear magnetic resonance spectroscopy (SSNMR) to the structural studies of mesoporous organic-inorganic hybrid catalytic materials. Most of these latest capabilities of solid-state NMR were made possible by combining fast magic angle spinning (at >= 40 kHz) with new multiple RF pulse sequences. Remarkable gains in sensitivity have been achieved in heteronuclear correlation (HETCOR) spectroscopy through the detection of high-gamma (H-1) rather than low-gamma (e.g., C-13, N-15) nuclei. This so-called indirect detection technique can yield through-space 2D C-13-H-1 HETCOR spectra of surface species under natural abundance within minutes, a result that earlier has been out of reach. The N-15-H-1 correlation spectra of species bound to a surface can now be acquired, also without isotope enrichment. The first indirectly detected through-bond 2D C-13-H-1 spectra of solid samples are shown, as well. In the case of 1D and 2D Si-29 NMR, the possibility of generating multiple Carr-Purcell-Meiboom-Gill (CPMG) echoes during data acquisition offered time savings by a factor of ten to one hundred. Examples of the studied materials involve mesoporous silica and mixed oxide nanoparticles functionalized with various types of organic groups, where solid-state NMR provides the definitive characterization.