The Influence of “Small Molecules” on Crystallization of TiO2 Xerogels

The sol-gel method was used for preparation of sols and the precursor sols were prepared from a mixture of titanium(IV) tetra-isopropoxide, isopropanol, water, nitric acid and “small molecule” as stabilizing reagent. The acetylacetone and acetic acid were used as small molecules (“stabilizers”). Three TiO2 xerogels were studied by DTA–TG analysis in combination with the XRD analysis. The crystallization was determined by non-isothermal analysis. The values of activation energy of crystallization were calculated using Johnson-Mehl-Avrami model. For xerogel without “small molecules” and xerogel with acetic acid, the activation energy of anatase crystallization is E = (1.07 ± 0.02)·105 J.mol-1 and E = (0.78 ± 0.02)·105 J.mol-1, respectively. According to Avrami coefficient M ∼ 1 for both xerogels, the mechanism of crystallization is surface nucleation. There is no crystallization of anatase in xerogel with acetylacetone.