Spectroscopic studies of interfacial structures of CeO2-TiO2 mixed oxides
Spectroscopic studies of interfacial structures of CeO2-TiO2 mixed oxides
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DOI：
10.1016/j.apsusc.2007.05.013
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发表时间：
2007-09-15
影响因子：
6.7
通讯作者：
Huang, Weixin
中科院分区：
文献类型：
--
作者：
Fang, Jun;Bi, Xinzhen;Huang, Weixin
利用X射线衍射（XRD）、高分辨X射线光电子能谱（XPS）、325 nm和514.5 nm激光激发的拉曼谱和扫描电子显微镜（SEM）等手段，对溶胶-凝胶法制备的不同Ce/TiO_2质量比的CeO_2-TiO_2复合氧化物的几何结构和电子结构进行了详细的研究。铈的存在有效地抑制了TiO 2由锐钛矿相向金红石相的相变。随着CeO 2含量的增加，TiO 2的XRD衍射峰不断衰减，但只有当Ce/TiO 2质量比达到0.50时，才出现立方相CeO 2的XRD衍射峰。CeO_2-TiO_2复合氧化物中TiO_2立方晶和CeO_2立方晶的平均晶粒尺寸小于单独TiO_2立方晶和CeO_2立方晶的平均晶粒尺寸。由514.5 nm激光激发的拉曼光谱法在Ce/TiO 2的重量比达到0.70之后检测CeO 2，而由325 nm激光激发的拉曼光谱法在Ce/TiO 2的重量比达到0.90之后检测CeO 2。XPS结果表明，Ti在CeO 2-TiO 2复合氧化物中以Ti4+的形式存在。在Ce/TiO 2重量比为0.05的混合氧化物中，Ce完全以Ce 3+的形式存在。随着Ce/TiO 2质量比的增加，Ce 4+占主导地位。基于这些结果，我们提出，CeO 2最初成核的缺陷（氧空位）内的TiO 2陶瓷，形成CeO 2和TiO 2陶瓷之间的氧桥接的界面。在界面处，Ce物种不能取代TiO_2晶格中的Ti ~（4+），而Ti ~（4+）可以取代CeO_2晶格中的Ce ~（4+）。氧空位浓度的降低、Ti-O-Ce界面的存在以及TiO 2微晶平均晶粒尺寸的减小都抑制了TiO 2微晶的相变。随着CeO 2含量的增加，CeO 2团簇不断生长并形成立方CeO 2纳米晶。光谱结果表明CeO-TiO_2复合氧化物的表面富集了TiO_2。(c)2007 Elsevier B. V.保留所有权利。
We have investigated the geometric and electronic structures of the cerium oxide (CeO2)-titanium dioxide (TiO2) mixed oxides with various Ce/TiO2 weight ratios prepared by the sol-gel method in detail by means of X-ray diffraction (XRD), high-resolution X-ray photoelectron spectroscopy (XPS), Raman spectroscopy excited by 325 and 514.5 nm lasers, and scanning electron microscope (SEM). Existence of cerium effectively inhibits the phase transition of TiO2 from the anatase phase to the rutile phase. XRD peaks of TiO2 anatase attenuate continuously with the increasing amount of CeO2 in the mixed oxide, but the XRD peaks of cubic CeO2 appear only after the weight ratio of Ce/TiO2 reaches 0.50. The average crystalline sizes of TiO2 anatase and cubic CeO2 in CeO2-TiO2 mixed oxides are smaller than those in the corresponding individual TiO2 anatase and cubic CeO2. Raman spectroscopy excited by the 514.5 nm laser detects CeO2 after the weight ratio of Ce/TiO2 reaches 0.70 whereas Raman spectroscopy excited by the 325 nm laser detects CeO2 after the weight ratio of Ce/TiO2 reaches 0.90. XPS results demonstrate that Ti exists in the form of Ti4+ in the CeO2-TiO2 mixed oxide. Ce is completely in the form of Ce3+ in the mixed oxides with a 0.05 weight ratio of Ce/TiO2. With the increasing weight ratio of Ce/TiO2, Ce4+ dominates. On basis of these results, we proposed that CeO2 initially nucleates at the defects (oxygen vacancies) within TiO2 anatase, forming an interface bridged with oxygen between CeO2 and TiO2 anatase. At the interface, Ce species cannot substitute Ti4+ in the lattice of TiO2 anatase whereas Ti4+ can substitute Ce4+ in the lattice of cubic CeO2. The decreasing concentration of oxygen vacancies, the Ti-O-Ce interface, and the decreasing average crystalline size of TiO2 anatase act to inhibit the phase transformation of TiO2 anatase. With the increasing amounts of CeO2, the CeO2 clusters continuously grow and form cubic CeO2 nanocrystals. Spectroscopic results strongly demonstrate that the surface region of CeO-TiO2 mixed oxide is enriched with TiO2. (c) 2007 Elsevier B.V. All rights reserved.