Abstract
Complex fumed nanooxides SiO2/Al2O3 (SA), SiO2/TiO2 (ST), and Al2O3/SiO2/TiO2 (AST) were studied using nuclear magnetic resonance spectroscopy, transmission electron microscopy, X-ray diffraction, infrared spectroscopy, adsorption, and quantum chemistry. Interior and surface contents of alumina in SA and AST are nonmonotonic functions of total Al2O3 content in contrast to that of titania in ST and AST. This is due to a larger difference in the precursor reactivity of sublimated Al2Cl6 and SiCl4 vapor than that for TiCl4 and SiCl4. Titania tends to form cores and silica (with alumina in AST) forms NPNP shells. Partially crystalline titania phase forms at lower content (∼9 wt%) than alumina remaining mainly amorphous even at CAl2O3 = 30 wt% (SA) or 22 wt% (A22S28T50). Chemical shift peak position in 29Si NMR spectra does not depend on CAl2O3 in contrast to CTiO2 due to different effects of dielectric alumina and semiconducting titania on magnetic shielding of the Si nuclei.
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