基于晶面效应和异质结效应协同作用的新型半导体光催化剂的理性构建与性能研究

Photocatalysis has long been considered as a cost-effective strategy to address the growing environmental crisis and energy shortage issues. How to rationally construct high-performance semiconductor photocatalysts is the key for photocatalysis. In the past decades, most researches regarding photocatalysis focus on exploring new photocatalytic materials and modifying them by means of introducing foreign dopants, co-catalysts, or organic sensitizers. By contrast, the essential influence from the surface structure of photocatalysts is often ignored. In theory, the photocatalytic activity of semiconductor nanocrystals is closely associated with their surface structures, especially the exposed facets, since the photocatalysis process occurs on the semiconductor surface. To the best of our knowledge, such facet-dependent photocatalytic activity of semiconductor nanocrystals has been scattered in many studies and thus systematic research on every semiconductor photocatalyst remian highly desirable to make clear facet-related mechanism. In this project, we will strive to prepare uniform a series of semiconductor nanocrystals with exposed well-defined facets by justing both thermodynamic and kinetic parameters in the crystal growth process. On this basis, we systematically investigate photocatalytic performance of semiconductor nanocrystals with different shapes and aspect ratios in photocatalytic degradation of pollutants and water splliting. Through thorough characterization and theoretical simulation on the surface structures, we expect to find the rules of such facet-dependent photocatalytic activity and make clear the mechanism for facet-induced separation between photoexcited electrons and holes. After that, we will explore effective methods to selectively deposit co-catalysts on those facets with oxidative or reductive function in photocatalysis, whereby the separation between photogenerated electrons and holes can be significantly improved and the valence band or the conduction band of semiconductor nanocrystals can be also tuned to appropriate position. Due to the synergism of facet effects and heterojunction effect, such specific facet-heterojunction based photocatalysts are anticipated to exhibit more excellent photocatalytic performance than those traditional photocatalysts based on random heterojunction. More importantly, the success in this study will inspire us to develop new methods to improve the performance of semiconductors by rationally constructing special heterostructures according to their crystallography anisotropy.

如何合理构建高效、稳定的半导体光催化剂体系是光催化应用的核心问题，而这一问题的解决依赖于我们对半导体光催化过程中本质问题的深入理解。传统的光催化研究主要集中在材料的开发和改性两个方面，忽略了光催化剂自身的表面结构对于其性能的影响。本项目拟在TiO2和BiVO4半导体光催化剂纳米晶体裸露晶面可控合成的基础上，系统地研究光催化过程中半导体光催化剂的晶面效应；根据光催化剂各晶面在光化学过程中所起的实际功能，在特定的晶面上选择性负载相应功能的助催化剂，以此方式将晶面效应与异质结效应有机的结合，通过它们的协同作用达到增强光生电子和空穴分离以及调整导带或价带位置的目的，最终构建出高效、稳定的光催化剂体系。我们希望上述研究结果，能为今后制备高效、稳定的新型半导体光催化剂提供一些指导，使我们能够摆脱过去"炒菜式"的合成方法。

如何合理构建高效、稳定的半导体光催化剂体系是光催化应用的核心问题，这一问题的解决依赖于我们对半导体光催化过程中本质问题的深入理解。然而，传统的光催化研究主要集中在材料的开发和改性两个方面，忽略了光催化剂自身表面结构对于光催化性能的影响。本基金的总体研究目的为：在实现半导体纳米晶体裸露晶面的可控合成的基础上，系统研究半导体光催化剂的晶面效应，进而依据各晶面光催化过程中的实际功能，选择性地负载具有相同功能的金属或半导体助催化剂，从而实现半导体光催化剂晶面效应和异质结效应的协同作用。经过项目组成员两年的不懈努力，本项目进展总体比较顺利，基本实现了既定的研究目标：（1）我们在TiO2、Cu2O等半导体纳米晶特殊晶面及界面的控制合成这一研究领域取得了一定的成绩，发展了多种调控微纳米晶体表面结构的方法，其中通过调控生长单元的过饱和度来实现对微纳米晶体形貌（表面结构）的调控这种方法的提出是对传统晶体生长理论的深化。（2）在实现TiO2、Cu2O等半导体表面结构调控的基础上，我们系统地研究了这些特定晶面的裸露晶面与材料光催化性质之间的关系，确认了光生电子-空穴在TiO2-{101}/{001}、Cu2O-{111} /{100}等半导体纳米晶的不同晶面上富集，从而表现出不同的光反应活性。（3）在确认半导体纳米晶光催化过程中晶面效应的基础上，通过光诱导还原/氧化等方式将金属或窄禁带半导体助（辅）催化剂选择性沉积到半导体光催化剂的特定晶面，合成得到了Fe2O3-TiO2-Pt、TiO2-{101}/Au@CdS等复合光催化剂，通过晶面效应与异质结效应合理的协同大大提高了复合光催化剂的催化活性。上述研究结果，将为今后制备高效、稳定的新型半导体光催化剂提供理论指导，摆脱过去“炒菜式”的合成方法。截止2016年底，在本基金的支持下，本项目组成员在国内外学术期刊上共发表学术论文13篇（12篇为SCI收录，其中IF>8的论文共7篇），包括2篇综述论文（包括1篇Nano Today）和11篇研究性论文（包括1篇Angew. Chem. Inter. Ed.），超过计划任务书的原定目标（4~8篇）。此外，培养毕业了1名博士和3名硕士。