CeO_2纳米晶的制备及其谱学性能研究

Study on the Preparation and Spectral Characteristics of CeO_2 Nanocrystallines

以硝酸亚铈为原料,浓氨水为沉淀剂,在80℃反应3h并陈化9h制备得到了纯CeO2纳米晶。XRD分析结果表明产物属于立方晶系。透射电镜观察发现产物呈六边形结构,推测为多面体形CeO2的投影,粒径在10nm左右,分散性良好。沉淀剂浓度、反应温度及陈化时间等对产物的纯度及形貌有明显影响。碱浓度降低或陈化时间缩短都导致产物中出现Ce(OH)3杂质;延长陈化时间,产物粒径增大;若反应温度低于40℃,产物中出现大量Ce(OH)3杂质。拉曼光谱研究表明,纯CeO2纳米晶在465cm-1处有一振动峰,对应于立方萤石结构的F2g拉曼位移,而含有Ce3+杂质的产物则在600cm-1处还出现一小峰。荧光光谱研究发现,在波长为400nm的激发光下,CeO2纳米晶在465nm附近出现一个不对称发射光谱峰。

Ceria （CeO2） nanoparticles were prepared by precipitation method using cerium nitrate（Ce（NO3）3·6H2O）and ammonia （25 Wt%） as raw materials under the reaction for 3 h and ageing for 9 h at 80 ℃ without any surfactants and further calcination. The powder X-ray diffraction （XRD） pattern shows the as-prepared CeO2 crystals belong to the cubic phase and are well crystallized. Transmission electron microscopic （TEM） studies reveal that the appearance of as-prepared CeO2 is hexagonal,which is proposed to be the projection of polyhedral shape. The regular fringes spacing of 0.31 nm is in agreement with the d value of （111） lattice planes of cubic phase CeO2 from high-magnification TEM image. Reaction conditions such as the concentration of precipitant,reaction temperature and ageing duration exert important influence on the purity and morphology of the product. Ce（OH）3 was detected when the reaction was processed at lower pH（〈9） or with ageing duration less than 8 h at 80 ℃. The size of polyhedral ceria nanoparticles increased with longer ageing time （〉15 h）. If the reaction went on at a temperature lower than 40 ℃,a large quantity of rodlike Ce（OH）3 was produced according to TEM observation. Raman spectra of CeO2 nanocrystallines exhibit a Raman shift at 465 cm^-1,corresponding to a F2g Raman band from the space group Fm3m of a cubic fluorite structure,while the Raman shift at about 600 cm^-1 may be attributed to the second Raman vibration mode of O2-vacancy due to Ce^3＋ impurity. Photoluminescence spectrum of CeO2 shows an emission at 465 nm at room temperature,which may be explained by charge transition from the 4f band to the valence band of CeO2.