原位同步辐射技术研究金属纳米团簇生长和表面修饰的动力学过程

Nano science and technology have brought on a profound innovation to modern society, which has urged people to seek and explore more novel nanomaterials with desired properties. One type of such novel materials is monolayer-protected metal nanoclusters, whose unique atomic configurations and electronic structures endow them with fascinating physicochemical properties and with promising applications in a variety of areas such as photonics, catalysis, sensing, and medicine. Developing new routes to synthesize and modify these nanoclusters is a key issue in this field, which requires a full understanding of the mechanism involved. In this project, based on the in situ synchrotron radiation XAFS/UV-vis absorption probing technique that is to be developed,and using other related technqiues, we aim to perform detailed kinetics studies on wet-chemical synthesis and post-growth surface modification processes of monolayer-protected Au, Ag nanoclusters. Focuses will be put on the temporal evolutions of reaction intermediates, cluster sizes, components, atomic and electronic structures, as well as optical features under various synthetic conditions. This project will also be dedicated to investigate the kinetic process of metal nanoclusters during their surface modification processes (ligand absorption, desorption, exchange, et al). Combined with theoretical calculations on the geometrical configuration, electronic structures of the clusters during these chemical reaction processes, it is hopeful to establish the componenet-structure-stability-property relationship for the nanoclusters. The execution of this project is promising to reveal at the atomic/molecular level the underlying mechanisms of clusters synthesis and surface modifications. It will also be hopeful to provide substantial theoretical and experimental basis for the synthesis of nanoclusters with controllable structures and physicochemical properties.

纳米科技对现代社会生产和生活带来深刻的技术变革，吸引着人们继续寻求和发展具有特定性质功能的新型纳米结构材料以满足日益增长的社会需求。单分子层保护的金属纳米团簇是一类新型纳米材料体系，具有独特的原子空间构型和奇异的物理化学性质，有着广阔的应用前景。发展新的团簇制备和改性方法并深刻了解其内在机制将大大促进团簇科学的发展。本项目拟发展和应用原位XAFS/UV-vis吸收谱学联合测量方法，并综合利用其他技术手段，多角度、多层次地研究单分子层保护的Au、Ag等金属纳米团簇在液相化学反应合成中的动力学演变规律；研究不同表面活性剂在团簇表面的吸附、脱附、交换的动力学行为。再结合对团簇几何构型、电子结构的理论计算，从原子分子水平上深入了解影响团簇合成的关键因素和表面修饰改性的内在机制，阐明团簇的组成、结构与稳定性和性能之间的相互关系，为设计合成新型的纳米团簇功能材料提供坚实的理论和实验基础。

本项目综合利用了同步辐射X吸收谱学技术(XAFS)、UV-vis吸收谱、TEM、质谱等方法，系统研究了一系列Au纳米团簇在不同的液相合成过程中的动态变化，深入研究了影响团簇形成和转化的关键因素，认识了不同反应条件下的动力学转变机制，并探讨了团簇的尺寸、组成、结构、光学和电学性质等之间的相互关系。首先联合原位XAFS/UV-vis吸收谱和质谱技术，研究了通过HCl刻蚀 “自上往下”形成1,3-双(二苯基膦)丙烷(L3)保护的Au13纳米团簇的动力学形成过程，揭示了在HCl作用下，从多分散纳米团簇出发，最终形成均一的单分散Au13(L3)4Cl4稳定团簇的反应历程。在常用的制备三苯基膦配体稳定的Au11团簇的基础上，我们通过在不同反应时段加入HCl，实现对反应中间产物的调控，选择性制备出尺寸不同的Au纳米团簇。还首次用氨水刻蚀法制备出了产率较高的单分散[Au6(PPh3)6]2+纳米团簇，原位ESI-MS和原位UV-vis对反应过程的探测使我们了解了该刻蚀反应形成团簇的机理。我们还利用刻蚀反应法制备出组成单一的可发出红色荧光(683 nm)的Au7(DHLA)2Cl2纳米团簇，并发现它可对水溶液中的ppm量级(0.2 ppm)浓度的微量Fe2+的选择性探测。利用一种新颖的前驱物Au(PPh3)2Cl，通过前前驱物控制方法，首次通过直接液相还原的方法直接制备了高产率的单分散[Au8(PPh3)7]2+团簇。此外，我们还合成了荧光[Au15(SR)2S12-14]+化合物，并利用不同比例的甲苯/乙醇进行溶剂效应研究，得到溶剂的极性与发光强度之间的定量关系。还研究了仅含有24个Au原子数的超小金纳米团簇的氧还原电催化性能。