UV Raman spectroscopic study on TiO2.: I.: Phase transformation at the surface and in the bulk
UV Raman spectroscopic study on TiO2.: I.: Phase transformation at the surface and in the bulk
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DOI：
10.1021/jp0552473
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发表时间：
2006-01-19
影响因子：
3.3
通讯作者：
Li, C
中科院分区：
文献类型：
--
作者：
Zhang, J;Li, MJ;Li, C
利用325和244 nm激光激发的紫外拉曼光谱、532 nm激光激发的可见光拉曼光谱、X射线衍射（XRD）和透射电子显微镜（TEM）研究了TiO2从金红石到金红石的相变。发现紫外拉曼光谱比可见拉曼光谱和XRD对TiO 2的表面区域更敏感，因为TiO 2强烈吸收紫外光。在较高温度下煅烧的样品通过UV拉曼光谱检测到的α相比通过可见拉曼光谱和XRD检测到的α相要高。上述三种方法所得结果的不一致性表明，在相转变过程中，表面区域的TiO2的锐钛矿相可以在相对较高的煅烧温度下保持。TEM结果表明，TiO2样品经高温煅烧后，小颗粒团聚成大颗粒，团聚过程沿着由金红石型向金红石型的转变。结果表明，团聚TiO2颗粒中的金红石相开始在团聚颗粒之间的界面处形成，即团聚TiO2颗粒内部区域的金红石相比团聚TiO2颗粒外表面区域的金红石相更容易转变为金红石相。当TiO2的纳米颗粒被高度分散的La2O3覆盖时，由于避免了纳米颗粒的直接接触并由La2O3占据了纳米颗粒的表面缺陷位点，体相和表面区域中的相变被显著地延迟。
Phase transformation of TiO2 from anatase to rutile is studied by UV Raman spectroscopy excited by 325 and 244 nm lasers, visible Rainan spectroscopy excited by 532 nm laser, X-ray diffraction (XRD), and transmission electron microscopy (TEM). UV Raman spectroscopy is found to be more sensitive to the surface region of TiO2 than visible Raman spectroscopy and XRD because TiO2 strongly absorbs UV light. The anatase phase is detected by UV Raman spectroscopy for the sample calcined at higher temperatures than when it is detected by visible Raman spectroscopy and XRD. The inconsistency in the results from the above three techniques suggests that the anatase phase of TiO2 at the surface region can remain at relatively higher calcination temperatures than that in the bulk during the phase transformation. The TEM results show that small particles agglomerate into big particles when the TiO2 sample is calcined at elevated temperatures and the agglomeration of the TiO2 particles is along with the phase transformation from anatase to rutile. It is suggested that the rutile phase starts to form at the interfaces between the anatase particles in the agglomerated TiO2 particles; namely, the anatase phase in the inner region of the agglomerated TiO2 particles turns out to change into the rutile phase more easily than that in the outer surface region of the agglomerated TiO2 particles. When the anatase particles of TiO2 are covered with highly dispersed La2O3, the phase transformation in both the bulk and surface regions is significantly retarded, owing to avoiding direct contact of the anatase particles and occupying the surface defect sites of the anatase particles by La2O3.