Dai Wen-Wu, Zhao Zong-Yan
Faculty of Materials Science and Engineering, Kunming University of Science and Technology, Kunming 650093, P. R. China.
Phys Chem Chem Phys. 2017 Apr 12;19(15):9900-9911. doi: 10.1039/c6cp08816c.
Composite photocatalysts with hetero-structures usually favor the effective separation of photo-generated carriers. In this study, BiOIO was chosen to form a hetero-structure with BiOI, due to its internal polar field and good lattice matching with BiOI. The interfacial properties and band offsets were focused on and analyzed in detail by DFT calculations. The results show that the charge depletion and accumulation mainly occur in the region near the interface. This effect leads to an interfacial electric field and thus, the photo-generated electron-hole pairs can be easily separated and transferred along opposite directions at the interface, which is significant for the enhancement of the photocatalytic activity. Moreover, according to the analysis of band offsets, the vertical BiOI/BiOIO belongs to the type-II hetero-structure, while the in-plane BiOI/BiOIO belongs to the type-I hetero-structure. The former type of hetero-structure has more favorable effects to enhance the photocatalytic activity of BiOI than that of the latter type of hetero-structure. In the case of the vertical BiOI/BiOIO hetero-structure, photo-generated electrons can move from the conduction band of BiOI to that of BiOIO, while holes can move from the valence band of BiOIO to that of BiOI under solar radiation. In addition, the introduced internal electric field functions as a selector that can promote the separation of photo-generated carriers, resulting in the higher photocatalytic quantum efficiency. These findings illustrate the underlying mechanism for the reported experiments, and can be used as a basis for the design of novel highly efficient composite photocatalysts with hetero-structures.
具有异质结构的复合光催化剂通常有利于光生载流子的有效分离。在本研究中，由于BiOIO具有内部极性场且与BiOI具有良好的晶格匹配，因此选择BiOIO与BiOI形成异质结构。通过密度泛函理论（DFT）计算详细研究并分析了界面性质和能带偏移。结果表明，电荷耗尽和积累主要发生在界面附近区域。这种效应导致产生界面电场，因此，光生电子 - 空穴对可以在界面处沿相反方向轻松分离和转移，这对于提高光催化活性具有重要意义。此外，根据能带偏移分析，垂直方向的BiOI/BiOIO属于II型异质结构，而面内方向的BiOI/BiOIO属于I型异质结构。前一种类型的异质结构比后一种类型的异质结构对提高BiOI的光催化活性具有更有利的效果。在垂直BiOI/BiOIO异质结构的情况下，在太阳辐射下，光生电子可以从BiOI的导带移动到BiOIO的导带，而空穴可以从BiOIO的价带移动到BiOI的价带。此外，引入的内电场起到选择器的作用，可以促进光生载流子的分离，从而提高光催化量子效率。这些发现阐明了所报道实验的潜在机制，并可作为设计新型高效异质结构复合光催化剂的基础。
