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

The structural characterisation of SiO2/ZrO2 nano-sol particles, prepared by mixing SiO2 sol and aqueous solution of ZrOCl2 8H2O, has been carried out 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/ZrO2 are compared with those of other references such as ZrO2, ZrOCl2 8H2O. BaZrO3, and ZrSiO4, and it becomes obvious that the Zr4+ ions are stabilised in an octahedral symmetry. The EXAFS result also indicates that each Zr atom is coordinated with six oxygen ones as the first nearest neighbour, where two oxygen atoms are from the linkage of (Si-O-Zr) at short distance, and 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 formation of (Si-O-Zr) bond at short distance and the second neighbour of silicon atoms increase simultaneously. From the above EXAFS and XANES results, the structural and gelating models could be proposed, which is based on the octahedrally coordinated but distorted zirconium species attaching on the SiO2 sol surface.