[2009月02月14日]

 

  继我组TiO2的紫外拉曼光谱研究工作在J. Phys. Chem. BJing Zhang, Meijun Li, Can Li et al., 2006DOI: 10.1021/jp0552473)发表后,引起国际国内同行的高度重视,被引用次数达52次之多。最近,我组TiO2的紫外拉曼光谱研究:. 纳米尺寸效应对体相/表面相变的影响又取得新的进展(Jing Zhang, Qian Xu, Can Li et al.,  J. Phys. Chem. C, 113 (5), 1698–1704, 2009http://dx.doi.org/10.1021/jp808013k)。 

    无论是在材料领域还是催化领域,人们发现TiO2的不同晶相结构对其作为材料和催化剂的性能有很大的差异。从应用的角度来看,人们总希望能根据实际的需要使锐钛矿向金红石的转变人为可控, 因此研究纳米TiO2的结构相变就显得具有很重要的现实意义。由于催化反应常常在催化剂表面上发生,所以TiO2的很多物理化学性质,特别是催化性能在很大程度上取决于其表面晶相结构。很多研究者对TiO2的相变机理进行了研究,但是现有的研究结果主要集中于氧化物体相晶相结构以及体相相变的信息,而针对TiO2表面晶相结构变化的研究却很少也是非常困难的。该工作利用紫外拉曼光谱的表面灵敏性并结合其他表征手段对不同粒子大小氧化钛的体相/表面相变进行了深入研究。TiO2的粒子大小对TiO2的相变起始温度和相变机理有很大影响。TiO2粒子越小,相变的温度越低;当TiO2的粒子小于60 nmTiO2的相变是主要从锐钛矿粒子相互接触的界面上开始发生的。当TiO2的粒子大于60 nm时,锐钛矿粒子的自由表面,界面,以及体相均可能成为金红石晶相的成核位。这个工作的意义在于为全面认识TiO2的相变机理,特别是体相/表面相变机理提供了指导意义,从而为控制体相/表面晶相提供了方法。

UV Raman Spectroscopic Study on TiO2. II. Effect of Nanoparticle Size on the Outer/Inner Phase Transformations
Jing Zhang, Qian Xu, Meijun Li, Zhaochi Feng, Can Li

J. Phys. Chem. C, 113 (5), 1698–17042009

Article. http://dx.doi.org/10.1021/jp808013k 

AbstractThe mechanism of the size-dependent outer/inner phase transformation in ultrafine TiO2 particles with narrowed size distribution was intensively investigated using UV Raman spectroscopy, X-ray diffraction, and transmission electron microscopy. Particle size is found to be the critical parameter determining the onset transition temperature and nucleation performance. The transformation temperature was decreased with the decrease of initial particle size. Rutile nucleates at interfaces of the contacting anatase grains (<60 nm). The free surface, interface, and bulk are all likely to work as rutile nucleation sites for large particles (d60 nm). Thermal stability of nanoscale titania is significantly enhanced by the presence of La2O3 even with surface coverage less than 5%, which blocks the outer/inner phase transformation of nano anatase. A model was devised to describe the phase transformation as a function of particle size and to predict the phase stability.

 

KeywordsSize-dependent outer/inner phase transformation UV Raman spectroscopy the onset transition temperature nucleation performance thermal stability