Chemical processes involved in the sol–gel preparation of an aluminium oxohydroxide gel from aluminium nitrate in organic medium

Abstract

Hydrolysis of aluminium nitrate in propan-1-ol leads to an aluminium oxohydroxide optically clear spinnable material as well as a slightly elastic, monolithic gel. The propanol has several roles in the hydrolysis. It dissolves the Al nitrate, induces the decomposition of the nitrate ions through nitric acid and promotes the hydrolysis and condensation of Al^III. Furthermore it reacts with nitric acid and/or its decomposition products resulting in formation of various oxidised derivatives of propan-1-ol. The products of the gel preparation, i.e. the organic compounds formed during heating of the aluminium nitrate–propan-1-ol mixture were investigated by gas chromatography as well as tandem MS techniques and UV–VIS spectroscopy. The coordination sphere of Al^III and the role of the organic compounds in building up the gel network has been studied by ²⁷Al MAS NMR and IR spectroscopy.