The structure of multicomponent (titania/zirconia) nanoparticles

The local structure of titania/zirconia nanoparticles has been investigated using small-angle neutron scattering (SANS). The colloids were prepared either by hydrolyzing a mixture of titanium and zirconium alkoxides, and peptizing the resulting hydrolyzate with nitric acid (homogeneous) or hydrolyzing a titanium alkoxide, and peptizing the hydrolysate with zirconium(IV) nitrate (heterogeneous). The final titania/zirconia and metal oxide/nitrate mole ratios were 16.0 and 10.0, respectively. The nanoparticles were crystalline anatase (crystallite size ca.8 nm) and amorphous zirconia. The results of SANS contrast-variation experiments are described. The minimum-contrast points for the homogeneous and heterogeneous colloids, determined using either the known analytic form of the scattering at q = 0 or the scattering invariant, gave similar results. Significant differences from the expected value were attributed to the sorption of nitrate counter-ions and hydroxyl species on the surface of the colloids. In both cases, the scattering at minimum contrast was consistent with a fractal network of uni-dimensional zirconia, with a typical diameter of similar to 1.5 nm. The results indicate that in the homogeneous colloids, the zirconia is segregated within the matrix of the titania crystallites (on similar to 1 nm scale), whereas in the heterogeneous colloids, the zirconia is segregated on the surface of the titania crystallites (on similar to 10 nm scale).