基于缺陷调控的Z型TiO2/g-C3N4光解水体系的设计与构建

Photocatalytic water splitting is an ideal way to solve energy and environmental issues, and Z-scheme play an important role in this process. Nowadays, the fabrication of Z-scheme mostly relies on unstable ion pairs or noble metal as charge mediator, it is still unclear whether Z-scheme can be formed when two semiconductors contact with each other directly. Defect inherently determines the charge transfer and band structure of semiconductor photocatalyst, therefore, this work aims at constructing Z-scheme by regulating defects in TiO2 and g-C3N4. Firstly, we will establish an approach to fabricate of TiO2 and g-C3N4 with controllable defect species and concentration by modulating the parameters during synthesis and post-treatment process, combining theoretical calculations with experimental results to illustrate the influence of defects over band structures. Then, semiconductors with different band structures were matched reasonably, and then its effect on band bending and charge transfer were studied, which will lead to the formation of optimal interface structure and thus improve the dynamic competition of directional Z-scheme electron transfer. Finally, highly-efficient Z-scheme water splitting systems were fabricated based on the direct interface contact of defective TiO2 and g-C3N4. Through this work, it is expected that the relationships between defect modulation, band structure and charge transfer mechanism can be revealed, and lay theoretical and methodological foundations for controllable construction of Z-scheme junctions that are free of charge transfer mediators.

光解水产氢是解决能源与环境问题的理想途径，Z型结在这一过程中具有重要作用。目前Z型结大多依赖不稳定离子对或贵金属作为电子传递媒介，而半导体直接界面接触能否形成Z型结尚不清楚。缺陷从本质上决定了半导体光催化剂的电荷传递及能带结构，因此本项目拟通过对TiO2和g-C3N4中缺陷的调控来构建Z型结。通过改进合成条件与后处理过程，建立缺陷种类和浓度可控的TiO2和g-C3N4制备方法，结合理论计算和实验结果阐述缺陷对二者能带结构的调制作用；合理匹配能带结构并研究其对能带弯曲和电荷传递机制的影响规律，以指导最优界面结构的构建来提高电子定向Z型传递的动力学竞争性，最终形成基于缺陷型TiO2和g-C3N4直接界面接触的高效Z型光解水体系。本项目的研究可望在理论上揭示缺陷调控、能带结构和电荷传递机制的构效关系，为不依赖电子传递媒介的Z型结的可控构建提供理论依据和方法基础。

光/电催化分解水制氢技术可有效解决当今世界所面临的能源和环境问题，其核心在于高效半导体光催化剂。Z型结是对自然界光合作用的人工模拟，在高效电荷分离的同时保持了强氧化还原能力，但是半导体直接接触时形成Z型还是II型异质结的机制尚不清楚。本项目以缺陷调控为手段，对组成Z型结两组分的能带结构进行精准调控，从而对能带弯曲方向人工干预，从本质上实现直接界面接触时电子的定向Z型传递。主要工作如下：.一、通过改进合成条件，首次实现TiO2中阳离子缺陷浓度的可控调控，并揭示了金属缺陷对电子自旋态的影响机制，极大地提高了电荷分离效率和表面催化反应选择性。.二、基于TiO2中氧缺陷和金属缺陷的调控，构建了量子点自修饰TiO2 p-n同质结，阐明了p-n同质结相比于II型结和p-n异质结的优势，显著提高界面电荷分离和传递效率。.三、将缺陷调控及p-n同质结思路拓展至ZnO体系，制备了纳米颗粒修饰的ZnO p-n同质结，表征了p-n同质结的特性，相比纯ZnO光催化性能提高5.8倍。.四、改进合成方法将金属缺陷型TiO2缩小至量子尺寸，合成了p-TiO2量子点/g-C3N4 p-n异质结，证明量子尺寸效应对p-n异质结光催化过程的促进作用。.五、利用TiO2表面金属缺陷原位负载极微量Au纳米颗粒，构建了界面高分散Au调控下p-TiO2/Au/g-C3N4 间接Z型结，实现金属缺陷与表面等离子效应的协同调控。.六、基于缺陷种类优化与能带结构匹配，以碳缺陷g-C3-xN4为基底，构建不依赖电子传输媒介的TiO2-x/g-C3-xN4直接Z型结，通过调节费米能级的位置实现TiO2/ g-C3N4复合体系由II型结向Z型结的转变。.本项目将缺陷调控与能带结构调控有机结合，创建了缺陷浓度和种类可控的半导体光催化剂合成方法，并建立了基于缺陷调控的直接Z型结可控制备新思路。