Cr掺杂金红石相TiO2(110)单晶薄膜的制备、表征及光催化活性

采用脉冲激光沉积术(PLD)同质外延生长了表面原子级平整的6%(原子比)Cr 掺杂的金红石相TiO₂(110)单晶薄膜, 采用扫描隧道显微镜(STM)、扫描隧道谱(STS)、X 射线光电子能谱(XPS)和紫外光电子能谱(UPS)对其进行了表征. 结果表明: Cr 掺杂对TiO₂(110)-(1×1)表面的形貌没有明显影响, 但是提高了掺杂薄膜在负偏压的导电性; Cr与晶格O键合而呈现+3价态, 由此在TiO₂的价带顶上方~0.4 eV处引入杂质能级. 紫外-可见光吸收谱显示薄膜的光吸收能力被扩展到~650 nm, 处于可见光范围. 借助STM以单个甲醇分子的光解反应检测了薄膜的光催化活性. 仅观察到紫外光照射下甲醇分子的脱氢反应, 在可见光照射下(λ>430 nm)甲醇分子没有发生反应, 表明单独的Cr掺杂可能不足以提高TiO₂在可见光下的催化活性.

Preparation, Characterization and Photocatalytic Activity of Cr-Doped Rutile TiO2(110) Single Crystal Thin Films

The growth of Cr-doped rutile TiO₂(110) homoepitaxial single crystal thin films was investigated using pulsed laser deposition (PLD) method. Surface morphology and electronic structure were characterized using scanning tunneling microscopy/spectroscopy (STM/STS), X-ray and ultraviolet photoemission spectroscopy (XPS/UPS). The optical absorption spectra were measured using ultravioletvisible (UV-Vis) absorption spectroscopy. From STM images, we observed that the atomic flat TiO₂(110)-(1×1) surface maintained at Cr doping concentration of 6% (atomic ratio), indicating a negligible effect of the Cr dopants on the surface morphology. The Cr doped ruteile TiO₂(110) film showed higher tunneling conductance than undoped rutile single crystal. XPS and UPS spectra indicated that Cr atoms bond to lattice O, exhibiting an +3 oxidation state of +3 and introducing an impurity state above the valence band maximum by 0.4 eV. The UV-Vis absorption spectrum of the Cr doped film showed an absorbance extended to ~650 nm, in a visible light range, which was consistent with the UPS spectra. Using the Cr-doped TiO₂ films, the dissociation of methanol molecules was only observed under the UV light illumination (wavelength shorter than 430 nm), however, the dissociation reaction was not observed under the visible light illumination (wavelength longer than 430 nm). Our results suggest that the monodoping by Cr element may not be sufficient to promote the visible light photoactivity of rultile TiO₂(110) surface.