Structural characterisation of binary SiO2/TiO2 nanoparticle aerogels by X-ray scattering

Abstract

The effect of SiO2 to TiO2 aerogels content on their local structure is evidenced from X-ray scattering measurements. TiO2-SiO2 aerogels were prepared by sol-gel method followed by supercritical drying with liquid CO2 and heat treatment. The local structure of TiO2-SiO2 system was investigated by analysing the atomic pair distribution function PDF, G(r), obtained from X ray scattering data The modified coordination radius values obtained for the first coordination spheres by addition of SiO2 denotes a diminution of the atom packing in this system. The PDF of the 300°C heat treated TiO2 aerogel sample shows well-defined features allowing an unambiguous structure search and refinement. In particular, the first peak in the PDF of the precursor phase is quite narrow and centered at about 1.9 Å, which is the Ti-O distance in Ti-O6 octahedra. This observation shows that well-defined Ti-O6 octahedra are already formed during the homogeneous precipitation stage of the chemical process. Inspecting the data from the analysis of the atomic pair distribution function G(r) one remarks the occurrence of Si-O pair as a first coordination formation at a distance of 1.49 Å and the interatomic distances at 2.18 Å for the first Si—Si and 3.58 Å for the second Si—Si bond.