三明治型双异质结单层复合催化剂的设计及其光催化增强作用机制

Constructing heterojunction is the one of the important foundation for designing a composited photocatalyst. This project aims at heterojunction structure for the lack of rational design and regulation and difficult characterization, and proposes a new idea to develop a molecular heterojunction with clear composition and interface structure for revealing its inherent nature and mechanism of photocatalysis and transmission of photoexcited charge carriers, and thus design a highly efficient composited photocatalyst. On the basis of the our previous findings on the self-assembly approach for preparing novel monolayer materials, we choose Bi2WO6 monolayer nanosheets of the lamellar Aurivillius compounds Bi2An-1BnO3n+3 (A = Sr, Ba, Bi; B = Ti, Mo, W) as a model catalyst, and design a series of sandwich-like double heterojunction monolayer photocatalysts with clear composition and interface structure by the stoichiometric reaction with Br- ions bonding to nanosheet surface layer to form the related metal halide or oxyhalide layer (such as, AgX, BiOX and LaOX et al) on Bi2WO6 monolayer nanosheet surface. The effect of chemical composition, interface structure, band gap structure and chemical states of double heterojunction photocatalyst on the photocatalytic performance and the separation and transfer rate of photoexcited carriers will be fully investigated. The enhanced photocatalytic reaction mechanism of heterojunctions will be revealed at molecular level. The general and special characters of the different heterojunction for photocatalysis will also be systematically studied. The molecular reaction model of heterojunction photocatalyst will be elucidated to provide a theoretical guide in the adjustment of photocatalytic performance. These studies have the most important signification for enriching the foundation of photocatalytic science and technology, and developing new type of efficient photocatalysts.

构建异质结是设计制备复合光催化剂的重要依据之一。本项目针对异质结缺乏可设计性、调控性和难于表征等问题，提出构筑化学组成和结构明确的“分子型”异质结来研究光生电荷传导机制和光催化作用本质，进而设计高效光催化剂的研究思路。拟选择Bi2WO6为代表的层状Aurivillius化合物为模型催化剂，基于前期发现的单分子层纳米片组装方法，通过给单层片表面层植入卤素离子并引入相应的金属卤化物或卤氧化物层（AgX、BiOX、LaOX等），构筑组成和结构明确的“三明治型双异质结”单层复合催化剂。研究化学组成、界面结构、能带结构和化学状态等对材料光生电荷分离、转移效率及光催化活性的影响，从分子层次上揭示异质结增强光催化作用的本质；研究不同组分异质结的共性和特性，建立异质结催化剂的分子作用模型，为调控异质结光催化剂性能提供理论依据。该研究对丰富光催化科学基础和设计开发高效光催化剂有重大的理论和实际意义。

构建异质结复合光催化剂是开发制备高效光催化剂的最可行策略之一，本项目构筑化学组成和结构明确的异质结来研究光生电荷传导机制和光催化作用本质，进而设计高效光催化剂的研究思路。设计制备了多种二维薄层光催化剂材料并在其基础上构建异质结复合光催化剂，这种二维薄层光催化剂及其异质结复合光催化剂表现出较一般催化剂材料更高的光催化活性，显著提升了光生电荷的分离和传输效率，增强异质结作用原理的认识。基于异质结的认识，我们提出设计界面异质结，平衡光生电子和空穴的迁移速率，是抑制光催化剂的光生电子-空穴复合，延长光生电荷寿命，提升光催化反应过程效率的关键突破口，构筑出Z-型异质结构的SiC@MoS2万寿菊型纳米花复合光催化剂。这个Z-型异质结恰好利用了SiC中电子的迁移率远远大于空穴迁移率，而MoS2中空穴迁移率大大高于电子迁移率的特性，使光生电子和光生空穴满足都快的要求，以快速平衡的迁移速率分别在SiC和MoS2上高效发生CO2的还原和H2O的氧化。进一步构建了Cu2O-Pt/SiC/IrOx复合材料结合反应器设计构造空间分离的串联Z型反应体系能有效提高CO2与H2O反应效率，与SiC@MoS2光催化剂相比，到甲酸的还原效率有非常大的提升，含碳化合物生成速率提高约60倍，这对未来的研究提供了一种重要思路，同时表明光催化H2O还原CO2有很好的发展前景，该研究工作为指导设计高效人工光合反应体系及器件，制备高效宽光谱响应的异质结构复合光催化材料提供了理论依据。 此外，在内置Pt 对锐钛矿/金红石二氧化钛异相结(A/R)光催化剂中，提出串联异质结的电荷转移机制。这些研究从分子层次上揭示异质结光生电荷的传导机制和光催化增强作用本质，增强对光催化过程的本质理解与认识，为构建和调控高效异质结复合光催化剂提供了新方法和策略。