Electronic Materials Research Laboratory, International Center for Dielectric Research, Key Laboratory of the Ministry of Education, School of Electronic & Information Engineering and ‡Frontier Institute of Science and Technology, Xi'an Jiaotong University , Xi'an 710049, Shaanxi, People's Republic of China.
ACS Appl Mater Interfaces. 2017 Nov 8;9(44):38984-38991. doi: 10.1021/acsami.7b11220. Epub 2017 Oct 24.
Spatial separation of photogenerated charges between different crystal facets has been observed in some semiconductor photocatalysts; however, the charge separation mechanism is still ambiguous. As a characteristic parameter of crystal facet, surface energy may be a crucial factor to dictate the flow of photogenerated charges. In this work, the relationship between surface energy and the flow mode of photogenerated charges is investigated by using model photocatalysts, including lance-shaped SnO particles and dodecahedral SnO particles. The former are enclosed by two kinds of crystal facets with a big gap in surface energy, while the latter are composed of two types of crystal facets with nearly equal surface energy. However, the experimental results exhibit that the photogenerated electrons flow to all exposed crystal facets randomly in both two kinds of SnO nanocrystals, which is opposite to what has been observed in extensively investigated semiconductor photocatalysts including TiO, SrTiO, BiVO, BiOCl, and CuO. Our results disqualify surface energy as an appropriate descriptor of preferential charge flow. Furthermore, the experimental results are confirmed by trapping energies and work functions calculated with the first-principles methods, which are proved to be more relevant parameters for describing the charge flow direction. Additionally, the trapping sites on each crystal facet are determined by charge analysis.
在一些半导体光催化剂中观察到了不同晶面之间光生电荷的空间分离；然而，电荷分离机制仍不清楚。作为晶面的特征参数，表面能可能是决定光生电荷流动的关键因素。在这项工作中，使用模型光催化剂（包括矛头状 SnO 颗粒和十二面体 SnO 颗粒）研究了表面能与光生电荷流动模式之间的关系。前者由两种晶面组成，表面能相差很大，而后者由两种类型的晶面组成，表面能几乎相等。然而，实验结果表明，在这两种 SnO 纳米晶体中，光生电子随机流向所有暴露的晶面，这与在广泛研究的半导体光催化剂（包括 TiO、SrTiO、BiVO、BiOCl 和 CuO）中观察到的情况相反。我们的结果否定了表面能作为优先电荷流动的合适描述符。此外，通过第一性原理方法计算的捕获能和功函数验证了实验结果，这证明它们是描述电荷流动方向的更相关参数。此外，通过电荷分析确定了每个晶面的捕获位置。
