在半导体纳米材料光催化体系中，光生电荷的分离是材料的核心。金属-半导体异质结能够增强半导体纳米材料的光催化活性，因为理论上异质结能在半导体内形成内建电场将光生电子空穴迅速分离。但是，纳米材料尺寸太小，无法利用宏观仪器直接测得内建电场，间接测试或理论推导由于材料纳米化本身所带来的物理化学性质的改变而失真，因此以纳米材料为载体的金属-半导体异质结的光催化机制的研究，很多结论只能停留在定性分析层面。由于ZnO单晶具有可观测的光催化效应，因此，申请人提出在ZnO单晶上构建金属-ZnO准块体体系替代现有的纳米体系，直接测试研究金属-半导体异质结的光催化电荷迁移过程。申请人拟在ZnO不同晶面上沉积不同功函数的金属，系统研究金属-半导体异质结内建电场及电荷迁移对半导体光催化机理机制的影响，并利用这一体系研究光催化加氢还原CO2反应机理。研究结果将对当前已工业化的热催化加氢还原CO2机理研究提供重要借鉴。

The seperation of photo-generated carrier is the core of materials in semiconductor nanomaterials photocatalytic system. Theoretically speaking, metal-semiconductor heterojunction can enhance the photocatalytic activity of the semiconductor nanomaterials for the heterojunction can form a built-in electric field which separating photo-generated electron-hole pairs rapidly in the semiconductor. However, the size of nano material is too small to measure the build-in field using any instruments directly. Moreover, Indirect test or theoretical derivation will be distorted due to the change of the physical and chemical properties of materials induced by nanocrystallization. In this condition, the study of mechanism of photocatalysis of metal-semiconductors based on nano material can only be stuck in the level of qualitative analysis. On the premise of ZnO single crystal with a observable photocatalytic effect, we proposed to build metal-ZnO quasi-block heterojunction system on the ZnO single crystal to replace the existing nanosystems, and then to study the photocatalytic charge migration process between the metal-semiconductor heterojunction. Firstly, we intend to deposit metals with different work function to the different crystal planes of the ZnO and systematically research the influence of the built-in electric field and charge transfer to the photocatalytic mechanism of semiconductor. Secondly, we intend to utilize this metal-ZnO quasi-block heterojunction system to study the photo-assisted direct hydrogenation of CO2. The research results will be provides an important reference to the mechanism study of industrialized thermocatalytic hydrogenation of CO2.