不同浓度Sn4+离子掺杂TiO2的结构、性质和光催化活性

摘要

采用溶胶-凝胶法制备出纯TiO2和不同浓度Sn4+离子掺杂的TiO2光催化剂(TiO2-Snx%, x%代表Sn4+离子掺杂的 TiO2样品中 Sn4+离子摩尔分数).利用 X 射线衍射(XRD)、X 射线光电子能谱(XPS)和表面光电压谱(SPS)确定了TiO2-Snx%催化剂的晶相结构和能带结构,结果表明：当Sn4+离子浓度较低时, Sn4+离子进入TiO2晶格,取代并占据Ti4+离子的位置,形成取代式掺杂结构(Ti1-xSnxO2),其掺杂能级在导带下0.38 eV处；当Sn4+离子浓度较高时,掺入的Sn4+离子在TiO2表面生成金红石SnO2,形成TiO2和SnO2复合结构(TiO2/SnO2), SnO2的导带位于TiO2导带下0.33 eV处.利用瞬态光电压谱和荧光光谱研究了TiO2-Snx%催化剂光生载流子的分离和复合的动力学过程,结果表明, Sn4+离子掺杂能级和表面SnO2能带存在促进光生载流子的分离,有效地抑制了光生电子与空穴的复合；然而, Sn4+离子掺杂能级能更有效地增加光生电子的分离寿命,提高了光生载流子的分离效率,从而揭示了TiO2-Snx%催化剂的光催化机理.%Pure TiO2 and Sn4+ doped TiO2 (TiO2-Snx%) photocatalysts were prepared by a sol-gel method, where x% represents the nominal molar fraction of Sn4+ ions in the TiO2 structure. The crystal structure and energy band structure of the resultant catalysts were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and surface photovoltage spectroscopy (SPS). The results show that for a low content of Sn4+ ions, the Sn4+ ions are doped into the TiO2 lattice and replace lattice Ti4+ ions in a substitute mode (Ti1-xSnxO2). The energy levels of these Sn4+ ions are located 0.38 eV below the conduction band. Moreover, the rutile SnO2 crystal structure evolves with increasing content of Sn4 + ions, i.e., a TiO2/SnO2 structure is formed. The conduction band of SnO2 is located 0.33 eV lower than that of TiO2. The separation and recombination mechanism of the photo-generated carriers was characterized by photoluminescence and transient photovoltage techniques. The results showed that the formation of the energy levels of Sn4+ ions and the conduction band of rutile SnO2 can enhance the separation of the photo-generated carriers, and suppress the recombination of photo-generated carriers. However, the energy levels of Sn4 + can lead to a much longer life time and higher separation efficiency of the photo-generated carriers. For different content of Sn4 + in Sn4 + ion doped TiO2 (TiO2-Snx%), the abovementioned aspects improve the photocatalytic activity.