Multinuclear Solid-state NMR Investigation of Nanoporous Silica Prepared by Sol-gel Polymerization Using Sodium Silicate

摘要

Multinuclear solid-state nuclear magnetic resonance (NMR) experiments were performed to investigate the local structure changes of nanoporous silica during hydrothermal treatment and surface modification with 3-aminopropyltriethoxysilane (3-APTES). The nanoporous silica was prepared by sol-gel polymerization using inexpensive sodium silicate as a silica precursor. Using ~1H magic angle spinning (MAS) NMR spectra, the hydroxyl groups, which play an important role in surface reactions, were probed. Various silicon sites such as Q~2, Q~3 Q~4, T~2, and T~3 were identified with ~(29)Si cross polarization (CP) MAS NMR spectra and quantified with ~(29)Si MAS NMR spectra. The results indicated that about 25% of the silica surface was modified. ~1H and ~(29)Si NMR data proved that the hydrothermal treatment induced dehydration and dehyroxylation. The ~(13)C CP MAS and ~1H MAS NMR spectra of 3-APTES attached on the surface of nanoporous silica revealed that the amines of the 3-aminopropyl groups were in the chemical state of NH~(3+) rather than NH2.