Structural and rheological aspect of mesoporous nanocrystalline TiO2 synthesized via sol-gel process

Mesoporous nanocrystalline titanium dioxide was prepared via the sol-gel technique using titanium glycolate as precursor in 1 M HCl solution at various HCl:H2O ratios. XRD analysis indicates the anatase phase forms at calcination temperatures in the range 600-800 degreesC. From the average grain sizes, we deduce that the nucleation rate dominates the kinetics at lower temperature, and growth rate becomes the controlling factor at higher temperature for materials prepared at HCl:H2O ratios of 0.28 and 0.33. At higher volume ratios, the growth rate appears to be the dominant factor at all temperatures. The highest specific surface area (BET) obtained was 125 m(2)/g at the HCl:H2O ratio of 0.28. A small decrease of specific surface area was observed from low to high acid ratio and a substantial decrease from lower to higher temperature. The material calcined at 800 degreesC was found to consist primarily of spherical particles with diameters smaller than 1 mum. Application of the Winter rheological criteria for the gel point indicates that the gelation time increases with increase of the HCl:H2O volume ratio. The fractal dimension of the critical gel cluster decreases with acid ratio, whereas the gel strength increases with acid ratio. Thus, increase of acidity leads to a less dense but stronger network structure. (C) 2003 Elsevier Inc. All rights reserved.