Electron Microscopy Center of Chongqing University, College of Materials Science and Engineering, Chongqing University , Chongqing 400044, China.
School of Chemistry and Biochemistry, Georgia Institute of Technology , Atlanta, Georgia 30332, United States.
ACS Appl Mater Interfaces. 2017 May 17;9(19):16620-16626. doi: 10.1021/acsami.7b01701. Epub 2017 May 8.
Photoinduced oxygen vacancies (OVs) are widely investigated as a vital point defect in wide-band-gap semiconductors. Still, the formation mechanism of OVs remains unclear in various materials. To elucidate the formation mechanism of photoinduced OVs in bismuth oxychloride (BiOCl), we synthesized two surface hydroxyl discrete samples in light of the discovery of the significant variance of hydroxyl groups before and after UV light exposure. It is noted that OVs can be obtained easily after UV light irradiation in the sample with surface hydroxyl groups, while variable changes were observed in samples without surface hydroxyls. Density functional theory (DFT) calculations reveal that the binding energy of Bi-O is drastically influenced by surficial hydroxyl groups, which is intensely correlated to the formation of photoinduced OVs. Moreover, DFT calculations reveal that the adsorbed water molecules are energetically favored to dissociate into separate hydroxyl groups at the OV sites via proton transfer to a neighboring bridging oxygen atom, forming two bridging hydroxyl groups per initial oxygen vacancy. This result is consistent with the experimental observation that the disappearance of photoinduced OVs and the recovery of hydroxyl groups on the surface of BiOCl after exposed to a HO(g)-rich atmosphere, and finally enables the regeneration of BiOCl photocatalyst. Here, we introduce new insights that the evolution of photoinduced OVs is dependent on surface hydroxyl groups, which will lead to the regeneration of active sites in semiconductors. This work is useful for controllable designs of defective semiconductors for applications in photocatalysis and photovoltaics.
光致氧空位（OVs）作为宽带隙半导体中的一种重要点缺陷而被广泛研究。然而，OVs 在各种材料中的形成机制仍不清楚。为了阐明 BiOCl 中光致 OVs 的形成机制，我们根据在 UV 光照射前后羟基基团显著变化的发现，合成了两个表面羟基离散样品。值得注意的是，在有表面羟基的样品中，经 UV 光照射后很容易获得 OVs，而在没有表面羟基的样品中则观察到了变化。密度泛函理论（DFT）计算表明，表面羟基基团强烈影响 Bi-O 的结合能，这与光致 OVs 的形成密切相关。此外，DFT 计算表明，吸附水分子通过质子转移到相邻的桥氧原子上，容易离解成单独的羟基基团，在每个初始氧空位处形成两个桥接羟基基团，从而在能量上是有利的。这一结果与实验观察结果一致，即在富含 HO(g) 的气氛中暴露后，BiOCl 表面的光致 OVs 消失和羟基基团恢复，最终使 BiOCl 光催化剂得以再生。在这里，我们引入了新的见解，即光致 OVs 的演化取决于表面羟基基团，这将导致半导体中活性位点的再生。这项工作对于用于光催化和光电的缺陷半导体的可控设计是有用的。
