NMR characterization on the preparation of sol-gel derived mixed oxide materials

The hydrolysis and polycondensation reaction of titanium(IV) isopropoxide w as chemically modified by acetylacetone, ethylacetoacetate, and triethanola mine. The reaction rates of these modified isopropoxides were investigated by H-1 NMR spectroscopy. The structural changes and effects of these chelat ing ligands upon the formation of Ti-alkoxide sol and TiO2 gel powders were investigated by H-1, C-13 NMR, IR spectroscopy and the dynamic light scatt ering method. The modified titania-silica mixed oxides prepared by sol-gel techniques were characterized by FT-IR, H-1 and C-13 NMR and Si-29 NMR spec troscopy. The degree of cross-linking of the silica network was inferred fr om the frequency of the Si-O-Si skeletal vibration. The formation of Si-O-T i(H) bridges was monitored by the intensity of the characteristic 945-960 c m(-1) vibration in a FT-IR spectrum. Si-29 NMR spectra of these gel powder was characterized by broad lines over the three types of sites. Different c ontributions, which were observed for Q(2), Q(3) and Q(4) sites in these mi xed oxide samples, were related to the types of ligand used on modified tit anium precursors. The extent of condensation reactions was inferred from th e fracture of completely cross-linked Q4 sites and these sites were increas ed with an elaborated temperature. (C) 2001 Published by Elsevier Science L td.