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

By a recently developed sol-gel process - treating Al(NO3)(3) . 9H(2)O in 1 -propanol - excellently spinnable material as well as slightly elastic tran sparent bulk hydrogel had been prepared. In this work the short- and interm ediate-range structure of the two different products were investigated by m eans of Al-27 MAS NMR and small-angle X-ray scattering. In the spinnable ma terial Al(III) ions are linked mainly through carboxylates by weak bonding, and build up a semi-ordered network. In contrast, in the hydrogel Al-oxohy droxide-acetate oligomers are found, the connectivity is maintained by shar ed OH, O and acetate ions. These oligomers form the elementary units, which build up large aggregates. The slightly elastic gel is essentially a porou s network of Al aggregates, where the pores are filled with water. With dry ing, both the arrangement and the inner structure of the aggregates are get ting more compact, resulting in a transparent, glass-like material. (C) 199 9 Elsevier Science B.V. All rights reserved.