基于卟啉类配体的多酸基MOFs的设计合成及光还原CO2性能研究

The use of solar energy for carbon fixation is an ideal way to promote energy cycle. The technology of photoreduction of CO2 has great significance to realize carbon recycling. This project aims to combine porphyrin, polyoxometalate and metal-organic frameworks (MOFs) together, using the methods of in-situ synthesis and post-synthesis, to obtain a series of porphyrin-based polyoxometalate-MOFs photocatalysts. We will focus on the improvement of visible light absorption ability and charge carrier transfer efficiency contributed by the composite structure. After visible light irradiation, porphyrin in MOFs produces the charge carriers, and framework itself provides a platform for loading polyoxometalates; polyoxometalates facilitate the separation of photo-generated charge carriers due to its high redox activity. Reasonable design of the host and guest will improve the utilization ratio of solar energy and the transfer efficiency of photo-generated charge carriers; many parameters such as band gap, turnover number and selectivity of the reduction products effected by the structure of porphyrin ligands, the type of the polyoxometalate and the structure of the framework will be systematically studied; the enhanced photoreduction ability promoted by porphyrins and polyoxometalates and the mechanism of this material will be also discussed. The results of this project not only have important contribution to the basic research of MOFs and polyoxometalate, but also promote the development and theoretical innovation of the design and synthesis of composite materials.

利用太阳能固碳是推动能源物质循环的理想方式。光催化还原CO2技术对实现碳的循环利用具有重要的实际意义。本课题拟将卟啉、多酸和MOFs结合，运用原位合成和后修饰合成方法，制备一系列基于卟啉类配体的多酸基MOFs光催化剂，考查复合材料结构对提高其可见光吸收能力和载流子传输效率的影响。MOFs中的卟啉类配体吸收可见光，其框架结构为多酸提供负载平台；多酸发挥自身高氧化还原活性，实现光激发载流子的有效分离。通过合理设计搭配主客体提升催化材料的太阳光利用率和对光生电子-空穴的传输效率；系统分析卟啉配体结构、多酸类型和三维结构与材料的带隙、转化数（TON）、还原产物单一性之间的构效关系；阐明卟啉和多酸的协同效应对光还原性能的增强作用，揭示复合材料改善光还原性能的作用机制。本项目的研究不仅对MOFs和多酸的基础研究具有重要价值，同时也将促进复合材料设计合成和制备技术的发展与理论创新。

CO2的催化转化与清洁能源的利用在当今科研界备受瞩目，各类反应催化剂的设计成为多学科研究前沿。本项目中，将具有出色的电子传输性能的多酸和MOFs单点催化的优势结合起来，通过后修饰合成我们得到了一系列多酸基MOFs二元复合催化剂和多元复合催化剂。实验结果表明，孔道中的多酸可与MOFs金属催化中心形成定向电子传输通道，加速多电子传输过程，进而增大催化活性位点的电子密度，提升催化活性。POM@PCN-222(Co)电催化还原CO2为CO的法拉第效率可以达到96.2%，且在10小时以上保持稳定。这一结果为在分子层面上设计电子传输通道提供了理论和实验基础，结构多样性多酸的引入将为CO2RR催化剂的发展提供更多的机会和可能。进一步的，向多酸基二元复合材料中引入低毒、低成本且高催化活性的过渡金属硫化物MoS2，得到了具有优异产氢性能的三元复合材料。MoS2量子点的加入可与孔道中的多酸产生协同作用，在最佳负载量7.0 wt%且无任何贵金属做助催化剂的条件下，材料的产氢效率可以达到565.85 μmol·g-1·h-1。这一结果将为低成本、高效复合催化剂的合成提供新的研究思路。在该项目的资助下发表高于平均影响因子的SCI论文4篇，待发表SCI论文3篇。培养硕士生5名。