Ag(核)@Au(壳)纳米颗粒的制备及高温原位XAFS研究

用化学液相还原法制备Ag核Au壳的核壳结构Ag@Au纳米颗粒。用UV-vis、透射电子显微镜(TEM)、差示扫描量热仪(DSC)和X射线吸收精细结构谱(XAFS)进行表征。结果表明成功制备出均一稳定单分散的Ag@Au纳米颗粒,Ag核颗粒平均粒径约8 nm,Au外壳的厚度约3.5 nm。DSC谱显示核壳颗粒在合金化过程中300°C附近时,扩散最剧烈,500°C时已完全形成合金。从高温原位XAFS的径向结构函数(RSF)可清晰看到Au原子周围的局域结构在合金化过程中发生明显变化。用替代位法进行拟合,发现Au-Au键长由2.86增加到2.89,配位数由原来的8.0减为6.1,同时出现了2.1个Au-Ag配位键,而无序度在不断增大,且整个合金化过程主要是以代位扩散为主。

Synthesis of Ag@Au nanoparticles and their characterization of high temperature in-situ XAFS

Ag@Au core-shell nanoparticles were synthesized via chemical liquid phase reduction method.They were characterized by UV-Vis absorption spectroscopy,transmission electron microscopy(TEM),differential scanning calorimetry(DSC) and X-ray absorption fine structure(XAFS) spectroscopy.The Ag@Au nanoparticles are of uniform and stable monodisperse,with an average size of the Ag core of about 8 nm,and the Au shell thickness of about 3.5 nm.DSC spectra show that core-shell particles are the most dramatic diffusion in the alloying process around 300°C,and the alloy is completely formed at 500°C.From the high temperature in-situ XAFS and the RSF curves,significant changes are clearly seen in the local structure of Au atoms in the alloying process.By fitting the data with replacement method,the Au-Au bond length gradually becomes longer from 2.86 to 2.89 and the coordination bond from 8.0 to 6.1,with 2.1 Au-Ag coordination bonds and increased degree of disorder,at the alloy formation.The alloy process is mainly based on subrogation diffusion.