氮化碳基Z型光解水系统的构筑及其催化机理研究

The difficulty of overall water splitting under visible-light lies in the low quantum efficiency of photocatalytic oxygen production. Inspired by natural photosynthesis in green plants, we will attempt to develop a all-solid-state Z-scheme photocatalytic system by combining newly developed hollow graphic carbon nitride as the H2 photocatalyst (PSⅠ), and semiconductor, which CB potential is more positive than the water oxidations potential to O2, as the O2 photocatalyst (PSⅡ), with solid-state electron mediator, to achieving overall water splitting under visible-light. Furthermore, the strategy of element-doping and cocatalyst-attachment will also be applied to tail the texture and surface properties, for the purpose of extending the response rang of visible spectra and enhancing the quantum efficiency of this Z-scheme overall photocatalytic water splitting system. To throw light on the mechanism and regulation principle of the all-solid-state Z-scheme system, we will systematically investigate the photocatalytic water splitting activity of these novel Z-scheme systems, and then, demonstrate the effects of the construction of all-solid-state Z-scheme system, as well as texture and surface modification, on the separation efficiency of photogenerated electron-hole pairs, and the formation of reactive oxygen species on the surface of Z-scheme, such as hydroxyl radical , superoxide anion radical and Hydrogen Peroxide. On the basis of above researches, the model of all-solid-state Z-scheme photocatalytic overall water splitting under light irradiation will be proposed. This research will open a new pathway for photocatalytic overall water splitting under visible light.

针对光催化氧化水半反应量子效率低而难以实现可见光全解水的重大难题，模拟绿色植物的光合作用，提出以申请人新近开发的具有高催化产氢活性的空心氮化碳作为产氢催化剂（PSⅠ），价带位置比O2/H2O 电位更正的半导体材料作为产氧催化剂（PSⅡ），配以合适的固相电子中介体，构筑全固态Z 型光催化系统，实现可见光催化全解水。并通过元素掺杂和附载助催化剂对催化剂进行体相和表面改性，实现更宽可见光谱响应范围和更高量子化效率的光催化全解水。系统考察不同类型氮化碳基Z 型系统的光催化分解水性能；研究Z 型光催化系统的构建、体相和表面改性对光生电子-空穴对的分离及界面迁移、催化剂表面羟基自由基和超氧负离子自由基以及过氧化氢等活性氧物种形成的影响。阐明全固态Z型系统光催化全解水过程的作用机理及其调变规律，建立全固态Z 型系统光辐射下全解水的反应理论模型。该研究为实现可见光全解水开辟了一条新的途径。

氮化碳(C3N4)，作为一种新兴的可见光响应聚合半导体光催化材料，其合成、改性和光催化性能研究受到了越来越多的关注，并取得了不错的进展。本项目组针对其光催化量子效率低而难以实现可见光全解水的难题，围绕决定光催化剂性能的三个效率（光的吸收效率、光生载流子的分离效率和水分解反应效率），通过对氮化碳的形貌、晶相调控，元素掺杂，表面修饰和Z 型光催化系统的构筑，来提高氮化碳光催化分解水产氢、产氧效率，实现了可见光全解水。首先，我们采用硬模板可控合成了石墨相氮化碳（g-C3N4）空心球（HCNS）和空心多面体g-C3N4，并成功将产氢助催化剂（Pt）和产氧助催化剂(Co(OH)2)选择性沉积在空心氮化碳球的内外表面。在提高光生载流子分离效率的同时阻止了分解水逆反应的发生，从而实现了可见光催化全解水，开发了氮化碳空心结构制备的通用方法。其次，我们以第一性原理研究了不同结构单元氮化碳聚合半导体的电子结构和能带结构，以及表面电子转移修饰以（SCTD）对其能带结构和光电性能的影响。以此为理论指导，我们分别设计合成了碳自掺杂g-C3N4（UCN-X）、氮掺杂石墨烯量子点修饰g-C3N4 (NGQDs(x) /g-C3N4)和ZnO量子点修饰的PTI（聚三嗪亚胺型氮化碳）纳米片异质结（PTI/ZnO-QDs），通过体相掺杂和表面修饰，实现了对光催化剂的能带调控和光生截流子分离的提高，从而增强光催化分解水活性。最后，我们通过构筑二元（TiO2/CNNs）、三元（PTI/ N-GQDs/ ZnO）Z型光催化系统，系统研究了Z型光解水过程中光生电子传输，并结合催化剂的微观结构、光电性能和光解水半反应产氢、产氧和全解水性能，初步提出了Z型光催化分解水机理。以上研究将为开发新型高效全解水催化剂提供新的思路和理论指导。