富氧空位型Bi/BiOX/g-C3N4复合光催化剂的设计合成及其可见光固氮机制研究

The development of catalysts with more adsorption active sites and high separation efficiency of charge carriers under visible light is the key to solve the problem of low photocatalytic nitrogen fixation activity. From the perspective of improving the nitrogen fixation performance under visible light, metal Bi/oxygen vacancy rich 2D-BiOX/2D-g-C3N4 ternary composite will be designed in this project. Photocatalytic nitrogen fixation performance of catalysts under visible light and the reaction mechanism will also be studied. By the synergistic effect of interface heterojunction, oxygen vacancy and surface plasma resonance effect of metal Bi, more N2 adsorption active sites, improvement of the photogenerated charge carriers separation efficiency and expansion of visible light response range can be expected, thus new type of visible light catalysts with highly efficiency can be obtained. ESR test, free radical capture reaction, MS analysis and photoelectrochemistry test will be applied to detect the active groups and intermediates during the catalytic process, and then to explore the interfacial electron mechanism of N2 reduction. The effects of elements composition, microstructure, oxygen vacancy and crystal facet on the nitrogen fixation performance will be discussed by combining the result of structure identification and physical characterization, thus the key factors for the improvement of activity can be clarified and the structure-activity relationship of the catalyst will be revealed. The study will provide experimental basis and theory reference for the design of high-efficient N2 photofixation catalysts under visible light and the develpoment of photocatalytic nitrogen fixation technology.

具有多吸附活性位点和高载流子分离效率的可见光催化剂的研发是解决光催化固氮效率低下问题的关键。本项目从提高光催化剂可见光固氮活性出发，设计合成金属Bi/富氧空位型2D-BiOX/2D-g-C3N4三元复合材料并开展其固氮性能及相关机理研究。通过构筑界面异质结、引入氧空位和金属Bi的表面等离子共振效应进行多级协同作用，可望增加催化剂的表面N2吸附活性位点、拓展催化剂可见光响应范围和提高其光生电子-空穴分离效率，从而获得高效稳定的可见光催化固氮材料。采用ESR测试、自由基捕获反应、质谱分析及光电化学等方法，检测催化过程中的活性基团和中间体，探明界面N2电子还原机理；结合结构鉴定和物性表征，探讨材料的组成、微结构、氧空位、晶面等对其固氮性能的调控机制，阐明催化活性提高的关键因素，揭示催化剂结构-性能间的构效关系。本项目的完成将为新型可见光固氮催化剂的研发及光催化固氮技术发展提供实验依据和理论参考。

氨不仅是生命体合成蛋白质的必需物质，而且是重要的能源储备材料。光催化固氮技术以太阳光为能源，以水为氢源，常温常压下通过光生电子还原N2合成NH3，具有绿色清洁、能耗低、可持续等优点，极有潜力替代传统工业固氮方法。然而固氮效率低下始终制约着光催化固氮技术发展，成为亟待解决的瓶颈问题。本项目从提高光催化剂可见光固氮活性出发，构筑吸附活化位点多、载流子分离效率高、可见光响应范围广的固氮材料，并对其催化性能和机理进行研究。项目内容主要分为三部分，首先，通过氢化处理引入氧空位，优化BiOX（X=Cl，Br，或I）单体，然后将BiOX单体分别与其它半导体BiOX、g-C3N4、ZnO等复合，通过表面构造“结”的方法来提高光生载流子的分离效率；其次，在BiOX/g-C3N4复合材料表面进一步负载Bi、Ag等金属构筑三元复合物光催化剂，研究结果表明得益于异质结、氧空位调节和金属Bi表面等离子共振效应的协同作用，与单体BiOBr和BiOX/g-C3N4相比，Bi/BiOBr/g-C3N4、Bi/BiOBr/g-C3N4等三元复合材料表现出了更优异的光催化固氮性能和循环稳定性；最后，我们还探索金属Fe离子掺杂BiOX光催化剂的制备及其固氮性能提升机理研究，结果表明铁离子的引入不仅改变了BiOX的能带结构，显著提高了其氧空位浓度，Fe3+还可以作为活性中心捕获电子参与反应，尝试将Fe-BiOI与g-C3N4复合则进一步提升了催化剂可见光固氮效率。综上，本项目采用金属表面负载、半导体复合、金属掺杂等方法引入表面等离子共振效应、构筑界面异质结、调节能带结构和氧空位，通过多级协同作用，增加催化剂表面的N2吸附活性位点、拓展催化剂可见光响应范围和提高其光生电子-空穴分离效率，获得了几种高效稳定的可见光催化固氮材料。采用多种物理化学表征方法相结合，探讨了材料的组成结构等对其固氮性能的调控机制，阐明光催化固氮机理和催化剂增效机制，揭示了催化剂结构-性能间的构效关系。项目的实施为高效可见光催化剂的研发和新型固氮体系的构建提供实验依据和理论参考。