In situ XAFS study at the Zr K-edge for SiO2/ZrO2 nano-sol

The structural characterisation of SiO2/ZrO2 nano-sol particles, prepared b y mixing SiO2 sol and aqueous solution of ZrOCl2 8H(2)O, has been carried o ut by in-situ XAS measurement at the Zr K-edge during condensation reaction . The detailed XANES features at the Zr K-edge of the mixed sol of SiO2/ZrO 2 are compared with those of other references such as ZrO2, ZrOCl2 8H(2)O, BaZrO3, and ZrSiO4, and it becomes obvious that the Zr4+ ions are stabilise d in an octahedral symmetry. The EXAFS result also indicates that each Zr a tom is coordinated with six oxygen ones as the first nearest neighbour, whe re two oxygen atoms are from the linkage of (Si-O-Zr) at short distance, an d four ones are from water molecules at long distance. As the condensation reaction proceeds, it is found that the number of oxygen atoms due to the f ormation of (Si-O-Zr) bond at short distance and the second neighbour of si licon atoms increase simultaneously. From the above EXAFS and XANES results , the structural and gelating models could be proposed, which is based on t he octahedrally coordinated but distorted zirconium species attaching on th e SiO2 sol surface.