能被长波光激发的具有高的光催化氧化和还原活性材料的设计、制备及机制研究

Developing high quantum efficiency and long wavelength-light activated composite photocatalyst via composition of two or more semiconductors is a main research direction to construct novel photocatalysts.In this project, two kinds of small band-gap semiconductors with low bottom of conduction band (LCB, such as In2S3, AgInS2 and g-C3N4) and high top of valance band (HVB, such as WO3, FeOOH, Bi(OH)CrO4) will be chosen as research object to prepare the composite photocatalysts. The research focuses on the effect of the sample's heterojunction interface structure formed between the two types of semiconductors and their content on the recombination of photoinduced electron and hole of the different semiconductors. The optimum conditions for the preparation of the samples will be determined.The recombination mechanism of the photoinduced electrons located in the semiconductor with HVB level between the photoinduced holes located in another semiconductor with LCB level will be revealed by means of (1) systematic investigations of the factors, including the photocatalysts' surface, crystal, and electronic structures, the interface composition, the chemical and coordination states of the composite atoms or ions,and the distribution of the surface elements, which affect the photocatalytic oxidation and reduction activities, and (2) subsequent theoretical calculations and the correlation analysis. The inherent laws of both the recombination of the photogenerated electrons and holes between the different semiconductors and the oxidation and reduction activity of the composite photocatalyst will be then clarified.The research will enrich not only the basic knowledge of photocatalysis, but also the photocatalytic reaction behavior of the semiconductor materials, and thus have important theoretical and practical significance.

发展能被长波光激发的、高量子效率的两种甚至多种半导体的复合光催化材料是构建新型光催化剂研究的主要方向。本项目以禁带宽度较小、导带底较负的半导体In2S3、AgInS2、g-C3N4及禁带宽度较小、价带顶较正的半导体WO3、FeOOH、Bi(OH)CrO4作为研究对象，重点研究上述两类半导体形成异质结的界面结构、组成等对不同光催化剂间光激电子-空穴复合的影响，阐明制备上述异质结光催化剂的最佳条件。通过对所制光催化剂的表面、晶体和电子结构、界面组成及原子或离子的化学状态、配位状态和表面元素分布等对光催化剂氧化和还原活性影响的系统研究，经过理论计算、进行关联分析，揭示异质结光催化剂中价带顶较正半导体的光激电子与导带底较负半导体的光激空穴复合的机制，阐明影响不同半导体间光激电子-空穴复合的本质规律。以上研究对丰富光催化的基础知识和半导体材料催化的反应特征都有重要的理论和实际意义。

针对异质结光催化材料太阳光利用率低、带-带转移后的光生电子-空穴具有相对较低的氧化-还原能力等缺陷，本项目根据光催化能带理论，将禁带宽度窄、价带顶较正和禁带宽度较小、导带底较负的两个半导体耦合组成能被长波光激发的全固态异质结Z-型光催化剂，该催化剂的光生电子具有高的光催化还原活性、而光生空穴具有较高的氧化活性。详细研究了禁带宽度窄、导带底较负的一类半导体材料（例如In2S3、CdS、AgInS2、NaNbO3、g-C3N4等）和另一类半导体材料即禁带宽度较小、价带顶较正的半导体（例如WO3、Bi2O3、Ag3PO4、Bi(OH)CrO4等）及上述两类半导体材料组成的异质结催化剂。重点研究上述两类半导体单体及组合形成异质结的界面结构、组成等对光生电子-空穴复合及转移的影响，得到制备上述单体及异质结光催化材料的最佳条件等。通过对所制光催化材料的表面结构、晶体结构和电子结构、界面组成及原子或离子的化学状态和表面元素分布等对光催化材料的氧化和还原活性影响的系统研究，通过检测反应体系中光生活性种类和光生电子-空穴转移和复合的光谱等，阐明异质结光催化剂中价带低较正半导体的光生电子-空穴与导带顶较负半导体的光生电子-空穴复合和转移的机制，揭示出影响不同半导体间光激电子-空穴复合和转移的本质规律和影响光催化剂氧化和还原活性的内在规律。例如WO3-g-C3N4光催化剂，当g-C3N4作为主体时，光生载流子遵循Z机制转移；当以WO3作为主体时，其光生载流子则采用带带间的普通转移。在Z型转移体系里，g-C3N4 价带上的空穴和WO3导带上的电子结合，致使光催化体系具有很强的光催化还原性和氧化性，光催化活性大幅度提升。然而，当WO3作为主体时，由于是普通的带带转移，所以转移后的光生电子和空穴，其光催化氧化和还原性能没有得到提高。本研究不仅为复合光催化剂的机理提供了崭新的认识，而且对指导高效异质结光催化剂的设计有着重要的科学与实际意义。