[2008年05月15日]

我组苏伟光等人关于“TiO2纳米粒子表面相的紫外拉曼和红外光谱研究”的工作发表在The Journal of Physical Chemistry CWeiguang Su, Jing Zhang, Zhaochi Feng, Tao Chen, Pinliang Ying, and Can Li,DOI: 2008. 10.1021/jp7118422)上。TiO2作为一种经典的半导体材料在催化领域中有着广泛的应用,氧化钛光催化分解水的发现,更是开创了多相光催化研究的新局面。实验表明TiO2不同的晶相特别是表面晶相结构对其作为材料和催化剂的性能有很大的差异。因为催化反应在催化剂表面上发生,所以TiO2的催化性能在很大程度上取决于其表面晶相结构。常规的表征手段例如XRD只能反映氧化物体相晶相结构的信息,到目前为止仍然缺少对金属氧化物表面晶相灵敏的表征方法。本研究利用紫外拉曼光谱和XRD详细考察了TiO2的相变过程以及相组成,然后利用CO和CO2吸附的红外光谱对不同晶相的TiO2样品进行了考察,结果发现紫外拉曼光谱的结果和红外光谱的结果相当一致,而与XRD的结果有着明显的差异,红外的结果进一步证实紫外拉曼光谱对氧化钛而言是一个表面灵敏的技术。红外光谱和紫外拉曼光谱均可以灵敏地探测氧化钛的表面相。在氧化钛的相变过程中,其表面相和体相是不同步的。


Abstract: Surface phases of TiO2 nanoparticles (30 ∼ 200 nm) were studied by UV Raman spectroscopy and FT-IR spectroscopy with CO and CO2 as probe molecules. UV Raman spectroscopy can differentiate the surface phase structure of TiO2 calcined at different temperatures. IR spectra of adsorbed CO and CO2 on TiO2 calcined at different temperatures are in good agreement with the results from UV Raman spectra. IR results evidently confirm that UV Raman spectroscopy is a surface-sensitive technique for TiO2. Both UV Raman and IR spectra indicate that the crystalline phase of TiO2 in the surface region is usually different from that in the bulk which is characterized by XRD. CO is weakly adsorbed on Ti4+ ions of anatase phase but is hardly adsorbed on those of rutile phase at room temperature. Adsorbed CO2 on anatase phase produces mainly bidentate carbonate, while on rutile phase produces mainly bicarbonate species. These results suggest that the surface Lewis acidity of anatase phase is stronger than that of rutile phase, and the concentration of cus Ti4+-O2- pairs on the surface of anatase phase is much higher than that on rutile phase; however, the basicity of surface OH groups of rutile phase is stronger than that of anatase phase.
Keywords: surface phase • TiO2 • IR spectroscopy • UV Raman spectroscopy • CO • CO2 • adsorption • phase transformation