Al-27 triple-quantum magic-angle spinning nuclear magnetic resonance characterization of nanostructured alumina materials

Abstract

The nanostructured transition aluminas were synthesized from an aluminum alkoxide precursor in the presence of various surfactants under hydrothermal conditions without any organic additives. The synthesized nanostructured alumina materials showed different morphologies depending on surfactants with high surface area, thermal stability, and aluminum sites of different coordination. The Al-27 triple-quantum (3Q) magic-angle spinning (MAS) NMR results showed that the samples prepared with cationic and nonionic surfactants consisted of mainly gamma-Al2O3 phase and a small amount of eta-Al2O3 phase due to the presence of the distorted tetrahedral site, but that the samples with anionic and neutral surfactants were predominantly i: the eta-Al2O3 phase. The experimental and calculated values of the electric field gradient (EFG) definitely suggested that cation vacancies were preferentially located at the octahedral sites in gamma-Al2O3 whereas at the tetrahedral sites in eta-Al2O3.