Cerium oxide nanoparticles coated by surfactant sodium bis(2-ethylhexyl) sulphosuccinate (AOT): local atomic structures and X-ray absorption spectroscopic studies

Cerium oxide nanoparticles coated by sodium bis(2-ethylhexyl) sulphosuccina te (AOT) were prepared by using a microemulsion method. Transmission electr on microscopy revealed an average particle size of 2-3 nm. X-ray diffractio n showed that the cerium oxide nanoparticles retain the CeF2-type cubic str uctures like the bulk crystal. The intermediate valence of formally tetrava lent compounds had been detected by x-ray-absorption near-edge structure (X ANES) spectra of Ce L-III absorption in bulk CeO2 and the cerium oxide nano particles. Two well resolved white lines can be assigned to the electron co nfigurations of 4f(0)L and 4f(1)L, respectively, where L denotes a ligand h ole. At the same time, the cerium oxide nanoparticles also showed the struc tural features of trivalent compounds, in comparison to the trivalent Ce(NO 3)(3) 6H(2)O, Four Lorentzian functions and two arctan functions were used to fit the normalized XANES spectra. The extended x-ray-absorption fine-str ucture (EXAFS) technique was used to probe the local atomic structures arou nd the absorber Ce. The multielectron excitation effect on the EXAFS spectr a was eliminated. A core-shell model was used to deduce the near-neighbour structural parameters around cerium. Bulk CeO2 with eight oxygen atoms loca ted at 2.343 Angstrom was used as the reference sample to extract the backs cattering amplitude and phase shift of the Ce-O bond. One half of the atoms locate at the core part with the CeF2-type cubic structures (eight oxygens at 2.343 Angstrom around Ce), the other half of the atoms are amorphous ph ase located in the shell part (surface of the nanoparticles) with approxima tely Ce2O3 structural features (averaged seven oxygens at 2.50 Angstrom ,ar ound Ce).