电子顺磁共振技术对纳米半导体光催化的检测策略研究

Semiconductor photocatalysis is of great significance for the treatment of environmental pollution and the development and utilization of clean renewable energy. While the degree of separation and recombination rate of photogenerated electron-hole pairs, as well as the production and kinetics of reactive oxygen species (ROS), are closely related to photocatalytic efficiency. Electrons, holes and ROS are transient species with extremely short lifetimes, which require ultra-fast laser spectroscopy and other precision instruments to detect these species. That brings great inconvenience to study the mechanism of photocatalysis. Electron paramagnetic resonance (EPR) has extremely high sensitivity and has been widely used in the research of free radical detection and photocatalysis mechanism. However, limited by the time resolution of conventional instruments and the representativeness of their sampling, EPR is mostly used for offline photocatalytic mechanism research. This proposal intends to firstly improve the time resolution of low temperature EPR and track the electron transfer process between photogenerated electron-hole pairs in semiconductor photocatalysis in real time. Then, through the modification of the existing EPR instrument, the EPR and ultraviolet-visible Spectrophotometer are combined online. And utilizing the spin trapping technology to capture the electron, the hole and the free radical. The online sampling of the free radical in the photocatalytic process is realized. Real-time monitoring for reaction kinetic analysis. The implementation of this proposal hopes to provide a new idea and means for the study of mechanism of photocatalysis.

半导体光催化对于环境污染治理以及清洁可再生能源的开发利用有着十分重要的意义。其中，光生电子-空穴对的分离程度与复合速率，以及活性氧物质的产量和动力学过程，与光催化效率紧密相关。电子、空穴以及活性氧均是寿命极短的瞬态物种，需要超快激光光谱等精密仪器进行探测，给光催化机理的研究带来了极大的不便。电子顺磁共振（EPR）具有极高的灵敏度，在自由基检测和光催化机理研究方面得到了广泛的应用。但受限于常规仪器的时间分辨率以及其取样代表性，EPR大多用于离线光催化机理研究。本项目拟首先通过低温EPR改善其时间分辨率，实时跟踪半导体光催化中光生电子-空穴对之间的电子转移过程。然后再通过对现有仪器的改造，实现EPR与紫外吸收在线联用，利用自旋捕获技术对瞬态电子、空穴和自由基进行捕获，实现光催化过程中的自由基的在线取样和实时监测，用于反应动力学分析。本项目的实施，将有望为光催化机理的研究提供一种新的思路和手段。

电子顺磁共振（EPR）在自由基检测反应机理研究方面具有广泛的应用。稳定自由基分子常常因为其优异的磁性特质被广泛应用在分子磁学等领域。以金属有机骨架化合物（Metal Organic Frameworks，MOFs）为代表的新型纳米多孔骨架材料在吸附，催化等领域具有广泛的应用。然而目前以自由基为配体的MOFs材料的研究仍然存在不足。在项目的支持下，本研究首先利用EPR对MOFs材料合成过程中的自由基配体及材料本身进行表征并探究其合成的机理。其次通过合成的稳定双自由基体系的EPR及光谱分析手段拓展了稳定性自由基在近红外区域的光热转换等方面的应用。最后搭建了原位电化学EPR检测手段，对具有有机记忆存储潜力的自由基体系进行原位的跟踪，通过在电化学氧化还原过程中的实时监测，提出可行性的机理。该方法拓展了EPR检测在自由基表征体系的应用范围。