Short- and intermediate-range structure in Al(III)-containing gels prepared from Al-nitrate in organic medium Original Research Article

By a recently developed sol–gel process – treating Al(NO3)3·9H2O in 1-propanol – excellently spinnable material as well as slightly elastic transparent bulk hydrogel had been prepared. In this work the short- and intermediate-range structure of the two different products were investigated by means of 27Al MAS NMR and small-angle X-ray scattering. In the spinnable material Al(III) ions are linked mainly through carboxylates by weak bonding, and build up a semi-ordered network. In contrast, in the hydrogel Al-oxohydroxide–acetate oligomers are found, the connectivity is maintained by shared OH, O and acetate ions. These oligomers form the elementary units, which build up large aggregates. The slightly elastic gel is essentially a porous network of Al aggregates, where the pores are filled with water. With drying, both the arrangement and the inner structure of the aggregates are getting more compact, resulting in a transparent, glass-like material.