A general nonaqueous route to crystalline alkaline earth aluminate nanostructures

Abstract

A nonaqueous route based on the solvothermal reaction of alkaline earth precursors with aluminium isopropoxide in benzyl alcohol is introduced. This simple process leads to crystalline complex nanostructures of alkaline earth aluminates, which, up to now, could only be obtained by solid state reaction at temperatures above 1100 °C or by sol–gel and further calcination at temperatures only slightly lower (∼800 °C). The approach appears to be rather general since under the same reaction conditions BaAl₂O₄, CaAl₄O₇, and SrAl₄O₇ could be obtained. The as-synthesized materials were characterized by X-ray diffraction, electron microscopy techniques, solid-state NMR and FT-IR spectroscopies. The reaction mechanism, which was studied as well, indicates the in-situ formation of benzoate species. These can preferentially bind to particular crystallographic facets of the aluminates via bridging bonds, thereby stabilizing the surfaces that give rise to the peculiar complex structure of the final material. In order to supplement the synthesis approach and to investigate the formation of impurity phases, pure aluminium oxide hybrid nanostructures were synthesized under similar conditions and fully characterized.