Harada Masafumi, Einaga Hisahiro
Department of Health Science and Clothing Environment, Faculty of Human Life and Environment, Nara Women's University, Nara 630-8506, Japan.
Langmuir. 2007 Jun 5;23(12):6536-43. doi: 10.1021/la0701071. Epub 2007 May 12.
Formation mechanisms of metal particles (gold (Au) particles) in an aqueous ethanol solution of HAuCl4 with poly(N-vinyl-2-pyrrolidone) (PVP) by the photoreduction method were investigated by UV-vis, transmission electron microscopy (TEM), and in situ and ex situ X-ray absorption fine structure (XAFS) analysis. The average diameters of the dilute and concentrated Au particles in PVP solution are estimated from TEM to be 106 A and 925 A, respectively. XAFS analysis was carried out to elucidate the reduction process of AuCl4- ionic species to metallic Au particles for the Au-L3 edge of the colloidal dispersions of the concentrated Au solutions. In the photoreduction process, the reduction of AuCl2- species to Au0 atoms is a slower process than that of AuCl4- to AuCl2-, and the reduction of AuCl2- to Au0 atoms and the association of Au0 atoms to form seed Au particles (particle diameter between 5.5 and 30 A) concurrently proceeds in the short-duration photoirradiation. In addition, in the long-duration photoirradiation, the slow progression of Au particle growth occurs with the association of Au0-Au0 metallic bonds, resulting in the formation of larger Au particles (particle diameter larger than 500 A).
通过紫外可见光谱、透射电子显微镜（TEM）以及原位和非原位X射线吸收精细结构（XAFS）分析，研究了在含有聚（N-乙烯基-2-吡咯烷酮）（PVP）的HAuCl4乙醇水溶液中，通过光还原法形成金属颗粒（金（Au）颗粒）的机制。从TEM估计，PVP溶液中稀Au颗粒和浓Au颗粒的平均直径分别为106 Å和925 Å。进行XAFS分析以阐明浓Au溶液胶体分散体中AuCl4-离子物种还原为金属Au颗粒的Au-L3边缘的还原过程。在光还原过程中，AuCl2-物种还原为Au0原子的过程比AuCl4-还原为AuCl2-的过程慢，并且在短时间光照射下，AuCl2-还原为Au0原子以及Au0原子缔合形成种子Au颗粒（粒径在5.5至30 Å之间）同时进行。此外，在长时间光照射下，随着Au0-Au0金属键的缔合，Au颗粒生长缓慢进行，导致形成更大的Au颗粒（粒径大于500 Å）。
