PREPARATION OF ORGANIC-MODIFIED CERIA NANOCRYSTALS WITH HYDROTHERMAL TREATMENT

摘要

The effect of the organic stabilizing agents on the structure and the surface states of CeO_2 nanocrystals prepared by the hydrothermal synthesis has been investigated with infrared (IR) spectroscopy, X-ray diffraction (XRD) measurement and transmission electron microcscope (TEM) observation. Investigation on the temperature dependence of the nanocrystal size and shape in the hydrothermal treatment using oleate as a stabilizing agent clearly revealed the acceleration of the crystalline growth at high temperature. Hydrothermal syntheses of carboxylate-modified CeO_2 nanocrystals were performed using laureate and linoleate species in addition to oleate. XRD measurement indicated the formation of nanocrystalline CeO_2 in any case and no remarkable difference in crystalline structure or crystallite size. IR spectroscopy revealed the different surface states of CeO_2 nanocrystals, depending on the molecular structure of stabilizing agents, that laureate species having a short straight hydrocarbon chain made a simple bidentate coordination to CeO_2, while oleate made mixed coordination state of bidentate and unidentate. Linoleate species having a convoluted hydrocarbon chain indicated the bidentate coordination and the existence certain amount of free linoleic acid or linoleate species among CeO_2 nanocrystals. TEM observation indicated that laureate adsorbed on CeO_2 made the uniform interdigitation, while linoleate made more complicated connections with free linoleate species or linoleic acid.